preface chapter 1 electrical fundamentals · preface chapter 1 electrical fundamentals ... final...

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Preface......................................................................x

Chapter 1 Electrical FundamentalsUnit 1 Matter ...................................................................3

Introduction .................................................................31.1 Matter ..............................................................31.2 Atomic Theory ..................................................31.3 Law of Electrical Charges.................................41.4 Law of Atomic Charges ....................................5

Negative Atomic Charge ...................................5Positive Atomic Charge.....................................5

1.5 Charged Material (Static Charge)......................5Static Voltage ...................................................6Reducing Static Charge....................................6

1.6 Neutralizing a Charge.......................................61.7 Lightning..........................................................71.8 Lightning Protection .........................................7Unit 1—Summary .......................................................9Unit 1—Conclusion ...................................................10Unit 1—Practice Questions .......................................11

Unit 2 Electron Theory ...................................................15Introduction ...............................................................152.1 Electron Orbits ...............................................152.2 Valence Electrons...........................................162.3 Freeing Electrons from an Atom .....................162.4 Conductors.....................................................162.5 Insulators .......................................................172.6 Semiconductors .............................................172.7 Atomic Bonding..............................................172.8 Compounds....................................................17Unit 2—Summary .....................................................19Unit 2—Conclusion ...................................................20Unit 2—Practice Questions .......................................21

Unit 3 Magnetism..........................................................23Introduction ...............................................................233.1 The Natural Magnet .......................................233.2 Magnetic Polarities.........................................233.3 Magnetic Compass.........................................233.4 Magnetic Molecule .........................................243.5 Magnetic Properties .......................................24

3.6 How to Magnetize Iron ...................................243.7 Permanent and Temporary Magnets ...............243.8 Demagnetizing Magnets.................................253.9 Magnetic Lines of Force .................................253.10 Magnetic Materials.........................................253.11 Law of Attraction and Repulsion .....................253.12 Retentivity ......................................................263.13 Permeability ...................................................26Unit 3—Summary .....................................................27Unit 3—Conclusion ...................................................28Unit 3—Practice Questions .......................................29

Unit 4 Electricity ............................................................33Introduction ...............................................................334.1 Electrical Current Flow (Electricity) .................334.2 Electricity .......................................................34

Chemical Activity (Electrochemistry) ...............34Magnetism (Magnetoelectricity)......................34Light (Photoelectricity)....................................35Thermo Energy (Thermoelectricity) .................36Pressure (Piezoelectricity) ..............................36

4.3 Useful Purposes of Electricity .........................37Electrochemistry ............................................37Electromagnetism ..........................................37Heat (Resistance) ..........................................38Illumination (Lighting).....................................38

4.4 Danger of Electricity .......................................39Understanding Electrical Shock Hazard ..........39What Determines the Severity of Electrical Shock?........................................39Clearing a Ground Fault..................................40Fire ................................................................41Electrical Arc Blast .........................................41

4.5 National Electrical Code .................................42Unit 4—Summary .....................................................43Unit 4—Conclusion ...................................................45Unit 4—Practice Questions .......................................46

Unit 5 Electromagnetism ...............................................49Introduction ...............................................................495.1 Electromagnetism in a Wire............................495.2 Field Intensity.................................................505.3 Field Interaction..............................................505.4 Field Interaction of Loops ...............................50

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5.5 Electromagnetism in a Coil.............................515.6 Magnetic Core................................................515.7 Ampere and Turns ..........................................51Unit 5—Summary .....................................................52Unit 5—Conclusion ...................................................53Unit 5—Practice Questions .......................................54

Unit 6 Uses of Electromagnetism...................................57Introduction ...............................................................576.1 Basic Electric Meters......................................57

Voltmeter .......................................................58DC Voltmeter ..................................................58DC Ammeter...................................................58Clamp-on AC Ammeter...................................59Ohmmeters ....................................................60Wheatstone Bridge.........................................60Megohmmeter................................................60

6.2 Electric Motor ................................................60Motor Components.........................................60Understanding Motor Motion ..........................61

6.3 Electrical Generator........................................62DC Generator .................................................62AC Generator..................................................62

6.4 Electromagnetic Relay....................................63Contacts.........................................................63Holding Relay .................................................64

Unit 6—Summary .....................................................65Unit 6—Conclusion ...................................................67Unit 6—Practice Questions .......................................68

Chapter 1—Final Exam.............................................70

Chapter 2Basic ElectricityUnit 7 The Electrical Circuit ...........................................77

Introduction ...............................................................777.1 The Electrical Circuit ......................................777.2 Electron Current Flow Theory .........................787.3 Conventional Current Flow Theory ..................787.4 Voltage (Pressure) ..........................................787.5 Resistance .....................................................79

Conductor Resistance.....................................797.6 Electric Current ..............................................807.7 Power.............................................................807.8 Electrical Formulas.........................................80Unit 7—Summary .....................................................81Unit 7—Conclusion ...................................................82Unit 7—Practice Questions .......................................83

Unit 8 Math ...................................................................85Introduction ...............................................................858.1 Whole Numbers..............................................858.2 Decimal..........................................................858.3 Fractions ........................................................858.4 Percentages ...................................................868.5 Multiplier........................................................868.6 Percent Increase ............................................878.7 Reciprocals ....................................................878.8 Squaring a Number ........................................888.9 Square Root ...................................................898.10 Volume...........................................................898.11 Kilo ................................................................898.12 Rounding Off ..................................................908.13 Parentheses ...................................................908.14 Testing Your Answer for Reasonableness........91Unit 8—Summary .....................................................92Unit 8—Conclusion ...................................................93Unit 8—Practice Questions .......................................94

Unit 9 Electrical Formulas..............................................99Introduction ...............................................................999.1 Electrical Circuit .............................................999.2 Power Source...............................................100

Direct Current...............................................100Alternating Current .......................................100

9.3 Conductance ................................................1009.4 Circuit Resistance ........................................1019.5 Ohm’s Law...................................................1019.6 Ohm’s Law and Alternating Current ..............102


9.7 Ohm’s Law Formula Circle............................1029.8 PIE Formula Circle ........................................1039.9 Formula Wheel ............................................1049.10 Using the Formula Wheel..............................1049.11 Power Losses of Conductors ........................1059.12 Cost of Power...............................................1069.13 Power Changes with the Square

of the Voltage ...............................................107Power Example at 230V ...............................107Power Example at 208V ...............................107Power Example at 240V ...............................108

Unit 9—Summary ...................................................109Unit 9—Conclusion .................................................110Unit 9—Practice Questions .....................................111

Chapter 2—Final Exam...........................................115

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Chapter 3Basic Electrical CircuitsUnit 10 Series Circuits.................................................123

Introduction .............................................................12310.1 Practical Uses of the Series Circuit...............123

Lighting........................................................123Control Circuit ..............................................124Signaling Circuit ...........................................124Internal Equipment Wiring ............................124

10.2 Understanding Series Calculations ...............124Resistance ...................................................124Voltage.........................................................125Kirchoff’s Voltage Law..................................125Kirchoff’s Current Law .................................126Power...........................................................127

10.3 Series Circuit Calculations............................12710.4 Power Calculations.......................................12810.5 Variations .....................................................12810.6 Series Circuit Notes......................................12810.7 Series-Connected Power Supplies................128Unit 10—Summary .................................................130Unit 10—Conclusion ...............................................131Unit 10—Practice Questions ...................................132

Unit 11 Parallel Circuits ...............................................135Introduction .............................................................13511.1 Practical Uses of the Parallel Circuit .............135

Receptacle ...................................................135Lighting........................................................135Other Uses ...................................................135

11.2 Understanding Parallel Calculations..............137Voltage.........................................................137Kirchoff’s Current Law..................................137Power...........................................................138

11.3 Circuit Resistance ........................................138Equal Resistance Method .............................138Product-Over-Sum Method...........................139Reciprocal Method .......................................140

11.4 Parallel Circuit Notes ....................................14011.5 Parallel-Connected Power Supplies ..............141Unit 11—Summary .................................................142Unit 11—Conclusion ...............................................143Unit 11—Practice Questions ...................................144

Unit 12 Series-Parallel Circuits ....................................147Introduction ............................................................14712.1 Review of Series and Parallel Circuits ..........147

Series Circuit Review ...................................147Parallel Circuit Review..................................148

12.2 Working Series-Parallel Circuits ...................14812.3 Voltage.........................................................149Unit 12—Summary .................................................150Unit 12—Conclusion ...............................................151Unit 12—Practice Questions ...................................152

Unit 13 Multiwire Circuits ............................................153Introduction .............................................................15313.1 Neutral Conductor ........................................15313.2 Grounded Conductor ....................................15413.3 Current Flow on the Grounded

(Neutral) Conductor ......................................1542-Wire Circuit...............................................1543-Wire, 120/240V, Single-Phase Circuit ........154

13.4 Balanced Systems........................................15513.5 Unbalanced Current......................................155

3-Wire, 120/240V, Single-Phase Circuit ........1553-Wire Circuit from a 4-wire,Three-Phase System ....................................1564-Wire, Three-Phase Circuit .........................156

13.6 Multiwire Branch Circuit ...............................1562-Wire Circuit Voltage Drop ..........................157Multiwire Circuit Voltage Drop ......................157

13.7 Dangers of Multiwire Circuits .......................158Fire Hazard...................................................158Destruction of Equipment as Well as Fire Hazard...................................................158

13.8 NEC Requirements .......................................159Unit 13—Summary .................................................160Unit 13—Conclusion ...............................................161Unit 13—Practice Questions ...................................162


Chapter 4Electrical Systems and ProtectionUnit 14 The Electrical System......................................173

Introduction ............................................................17314.1 Current Flow ................................................17314.2 Utility Neutral Current Path ...........................173

Multipoint Neutral Ground ............................17314.3 Utility Ground-Fault Current Path ..................17414.4 Premises Neutral Current Path .....................174

Single Point Neutral Bond.............................17514.5 Premises Ground-Fault Current Path ............175

Earth as Ground Fault Path for Systems 600V or Less..................................175

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14.6 Utility High-Voltage Transmission Lines ........17514.7 Conductor Voltage Drop................................17514.8 Conductor Power Loss .................................176

Current.........................................................17614.9 Reducing Voltage Drop and Power Loss .......177

138 kV Transmission Line.............................17714.10 Generating Plants.........................................17714.11 Step-Up Substation at Generating Plant .......17714.12 Transmission Line ........................................17814.13 Step-Down Substation .................................17814.14 Primary Distribution Feeders ........................17814.15 Distribution Transformer ...............................17814.16 Secondary Distribution Line..........................178Unit 14—Summary ................................................179Unit 14—Conclusion ...............................................181Unit 14—Practice Questions ...................................182

Unit 15 Protection Devices ..........................................185Introduction .............................................................185Part A—Overcurrent Protection Devices ..................18515.1 Overcurrent Protection .................................185

Overload.......................................................185Ground Fault ................................................186Short Circuit .................................................186

15.2 Clearing Faults .............................................186Time—Current Curves .................................186Remove Dangerous Touch Voltage................186

15.3 Overcurrent Protection Device Types ............18715.4 Fuse.............................................................187

Construction.................................................187Overload Protection ......................................187Short-Circuit and Ground-Fault Protection ....187

15.5 Circuit Breaker Trip Elements .......................188Thermal Trip Element ...................................188Magnetic Trip Element..................................188

15.6 Circuit Breaker Types ...................................188Inverse-Time ................................................188Adjustable-Trip .............................................188Instantaneous-Trip........................................188

15.7 Available Short-Circuit Current .....................18815.8 Interrupting Rating .......................................18915.9 Short-Circuit Current Rating .........................19015.10 Current-Limiting Protection ..........................190Part B—Ground-Fault Circuit Interrupters ................19115.11 How a GFCI Works........................................19115.12 Neutral-to-Case Detection ............................19115.13 Line-to-Neutral Shock Hazard ......................192

15.14 GFCI Fails—Circuit Remains Energized ........19215.15 GFCI Test Button...........................................193Part C—Arc-Fault Circuit Interrupter........................19315.16 Arcing Definition...........................................19315.17 Series Versus Parallel Arc .............................193

Series Arc.....................................................193Parallel Arc...................................................193

15.18 AFCI and the NEC .........................................19415.19 AFCI—How They Operate.............................194Part D—Ground-Fault Protection of Equipment........19415.20 Ground-Fault Protection of Equipment

Definition......................................................194Unit 15—Summary .................................................195Unit 15—Conclusion ...............................................198Unit 15—Practice Questions ...................................199


Chapter 5Alternating CurrentUnit 16 Alternating Current ..........................................213

Introduction .............................................................21316.1 Current Flow ................................................21316.2 Why Alternating Current is Used ...................21316.3 How Alternating Current is Produced............21416.4 AC Generator................................................21416.5 Waveform.....................................................215

Direct-Current Waveform..............................215Alternating-Current Waveform ......................215

16.6 Sine Wave ....................................................216Sinusoidal Waveform....................................216Nonsinusoidal Waveform ..............................216

16.7 Nonsymmetrical Waveform...........................21616.8 Frequency ....................................................21616.9 Phase...........................................................21716.10 Degrees .......................................................21716.11 Lead or Lag..................................................217

Leading ........................................................217Lagging........................................................217

16.12 Values of Alternating Current ........................218Instantaneous Value .....................................218Peak Value ...................................................218Effective Value..............................................218RMS Value....................................................218

Unit 16—Summary .................................................219Unit 16—Conclusion ...............................................220Unit 16—Practice Questions ...................................221

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Unit 17 Capacitance ....................................................225Introduction .............................................................225

Capacitor Current Flow.................................22517.1 Charged Capacitor........................................22517.2 Electrical Field..............................................22617.3 Discharging a Capacitor ...............................22617.4 Determining Capacitance .............................227

Plate Distance ..............................................227Surface Area ................................................227Dielectric Strength .......................................227

17.5 Uses of Capacitors .......................................227Electronic Power Supplies ............................228

17.6 Phase Relationship.......................................228Unit 17—Summary .................................................229Unit 17—Conclusion ...............................................230Unit 17—Practice Questions ...................................231

Unit 18 Induction .........................................................233Introduction .............................................................23318.1 Self-Induction...............................................23318.2 Induced Voltage and Applied Current ............234

Opposes Current Flow..................................234Aids the Current Flow...................................234

18.3 Conductor AC Resistance .............................234Eddy Currents ..............................................235Skin Effect....................................................235

18.4 Impedance ...................................................23518.5 Conductor Shape..........................................235

Current.........................................................236Winding........................................................236Frequency ....................................................236

18.6 Magnetic Cores ............................................236Core Material ...............................................236Core Length .................................................236Core Area .....................................................236

18.7 Self-Induced and Applied Voltage .................23718.8 Current Flow ................................................237

Inductive Reactance .....................................23718.9 Phase Relationship.......................................23818.10 Uses of Induction .........................................238Unit 18—Summary .................................................239Unit 18—Conclusion ...............................................240Unit 18—Practice Questions ...................................241

Unit 19 Power Factor and Efficiency ............................245Introduction .............................................................245

Inductors and Capacitors..............................245

Part A—Power Factor ..............................................24519.1 Apparent Power (Volt-Ampere) .....................24519.2 True Power (Watts) .......................................246


19.3 Power Factor ................................................24619.4 Unity Power Factor .......................................24619.5 Power Factor Formulas.................................24719.6 Cost of True Power .......................................24819.7 Effects of Power Factor ................................248Part B—Efficiency ...................................................25019.8 Efficiency .....................................................25019.9 Efficiency Formulas ......................................250Unit 19—Summary .................................................252Unit 19—Conclusion ...............................................253Unit 19—Practice Questions ...................................254

Chapter 5 Final Exam ..............................................257

Chapter 6Motors, Generators, and TransformersUnit 20 Motors ............................................................265

Introduction .............................................................265Part A—Motor Basics ..............................................26520.1 Motor Principles ...........................................265

Stator ...........................................................265Rotor ............................................................266

20.2 Dual-Voltage AC Motors ...............................26620.3 Motor Horsepower Rating.............................26620.4 Motor Current Ratings ..................................267

Motor Full-Load Ampere (FLA) Rating ...........267Actual Motor Current ................................... 267Motor Full-Load Current (FLC) Rating ..........267

20.5 Calculating Motor FLA ..................................267Single-Phase................................................268Three-Phase.................................................268

20.6 Motor-Starting Current .................................26920.7 Motor-Running Current.................................26920.8 Motor Locked-Rotor Current (LRC)................26920.9 Motor Overload Protection ............................269

NEC Requirement .........................................270Part B—Direct-Current Motors ................................27020.10 Direct-Current Motor Principles ....................27020.11 Direct-Current Motor Types ..........................271

Shunt-Wound DC Motor................................271Series-Wound DC Motor ...............................271

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20.12 Reversing the Rotation of a DC Motor...........271Part C—Alternating-Current Motors.........................27120.13 AC Induction Motor.......................................27120.14 Alternating-Current Motor Types...................272

Squirrel-Cage Induction Motor......................272Synchronous Motor ......................................272Wound-Rotor Motor ......................................272Universal Motor ............................................273

20.15 Reversing the Rotation of an AC Motor .........273Unit 20—Summary .................................................274Unit 20—Conclusion ...............................................276Unit 20—Practice Questions ...................................277

Unit 21 Generators ......................................................281Introduction .............................................................28121.1 Direct-Current Generator ..............................281

Excitation Current.........................................28121.2 Alternating-Current Generator ......................28221.3 Three-Phase Generators...............................283Unit 21—Summary .................................................284Unit 21—Conclusion ...............................................284Unit 21—Practice Questions ...................................285

Unit 22 Transformers ...................................................287Introduction ............................................................28722.1 Transformer Basics .....................................287

Primary Versus Secondary ...........................287Mutual Induction ..........................................287

22.2 Secondary Induced Voltage ..........................28822.3 Autotransformers .........................................288

Step-Down Transformers..............................288Step-Up Transformers ..................................289

22.4 Power Losses...............................................289Conductor Resistance Loss ..........................289Flux Leakage Loss .......................................289Eddy Currents ..............................................290Hysteresis Losses.........................................290

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22.5 Harmonic Current .........................................29022.6 Efficiency .....................................................29122.7 Transformer Turns Ratio ...............................29122.8 Transformer kVA Rating................................29222.9 Current Flow ................................................29222.10 Current Rating..............................................293Unit 22—Summary .................................................295Unit 22—Conclusion ...............................................296Unit 22 - Practice Questions ....................................297


Basic Electrical Theory Final Exam .........................................................309

Basic Electrical Theory Final Conclusion ............................................324

Annex A—Grounding and Bonding

Introduction .............................................................325Understanding the Basics of Electrical Systems.......326Understanding Electrical Shock Hazard....................328What Determines the Severity of Electrical Shock....328Clearing a Ground Fault ...........................................329Why Grounding is Often Difficult to Understand .......330250.1 Scope...........................................................333250.2 Definitions....................................................333250.3 Other Code Sections.....................................334250.4 General Requirements for Grounding and

Bonding........................................................335250.4(A) Summary ..................................................340250.6 Objectionable (Neutral) Current ....................345

Index ......................................................................347

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Article 90—Introduction ...................................................190.1 Purpose of the NEC.....................................................190.2 Scope of the NEC........................................................290.3 Code Arrangement.......................................................490.4 Enforcement ................................................................590.5 Mandatory Requirements and Explanatory

Material........................................................................690.6 Formal Interpretations .................................................690.7 Examination of Equipment for Product Safety ...........690.9 Units of Measurement .................................................7

Article 90 Questions....................................................8

Chapter 1—General ............................................................9

Article 100 Definitions.........................................................11

Article 110 Requirements for Electrical Installations ...........................................................................31

Part I. General Requirements.................................................31110.1 Scope .........................................................................31110.2 Approval of Equipment .............................................31110.3 Examination, Identification, Installation, and

Use of Equipment......................................................31110.4 Voltages .....................................................................32110.5 Copper Conductors....................................................32110.6 Conductor Sizes.........................................................32110.7 Conductor Insulation .................................................33110.8 Suitable Wiring Methods...........................................33110.9 Interrupting Protection Rating...................................33110.10 Short-Circuit Current Rating.....................................34110.11 Deteriorating Agents..................................................35110.12 Mechanical Execution of Work .................................36110.13 Mounting and Cooling of Equipment .......................37110.14 Conductor Termination..............................................37110.15 High-Leg Conductor Identification ...........................41110.16 Flash Protection Warning ..........................................42110.21 Manufacturer’s Markings ..........................................42110.22 Identification of Disconnecting Means .....................43

Part II. 600V, Nominal or Less ................................................43110.26 Spaces About Electrical Equipment ..........................43110.27 Guarding ....................................................................48

Article 110 Questions................................................49

Chapter 2—Wiring and Protection ..............................51

Article 200 Use and Identification of Grounded Neutral Conductor ................................................................53

200.1 Scope .........................................................................54200.6 Identification of the Grounded Neutral

Conductor ..................................................................54200.7 Use of White or Gray Color ......................................56200.9 Terminal Identification ..............................................57200.10 Identification of Terminals ........................................57200.11 Polarity ......................................................................57


Article 210 Branch Circuits ................................................59

Part I. General Provisions .......................................................59210.1 Scope .........................................................................59210.2 Other Articles ............................................................60210.3 Branch-Circuit Rating ...............................................60210.4 Multiwire Branch Circuits.........................................60210.5 Identification for Branch Circuits .............................62210.6 Branch-Circuit Voltage Limitation ............................63210.7 Branch-Circuit Receptacle Requirements .................63210.8 GFCI-Protected Receptacles .....................................64210.11 Branch-Circuits Required..........................................68210.12 Arc-Fault Circuit-Interrupter (AFCI) Protection.......71210.18 Guest Rooms and Guest Suites .................................71

Part II. Branch-Circuit Ratings ...............................................71210.19 Conductor Sizing.......................................................71210.20 Overcurrent Protection ..............................................73210.21 Outlet Device Rating .................................................74210.23 Permissible Loads......................................................74210.25 Common Area Branch Circuits .................................75

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Understanding the National Electrical Code, Volume 1 Table of Contents

Part III. Required Outlets ........................................................75210.50 General ......................................................................75210.52 Dwelling Unit Receptacle Outlet Requirements .......75210.60 Receptacles in Guest Rooms or Guest Suites for

Hotels and Motels......................................................81210.63 Heating, Air-Conditioning, and Refrigeration

Equipment (HACR)...................................................82210.70 Lighting Outlet Requirements ...................................82


Article 215 Feeders .............................................................87215.1 Scope .........................................................................87215.2 Minimum Rating .......................................................87215.3 Overcurrent Protection ..............................................88215.8 High-Leg Conductor Identification ...........................89215.10 Ground-Fault Protection of Equipment.....................89215.12 Identification for Feeders ..........................................89


Article 220 Branch-Circuit, Feeder, and ServiceCalculations ...........................................................................93

Part I. General .........................................................................93220.1 Scope .........................................................................93220.3 Application of Other Articles ....................................93220.5 Calculations ...............................................................94

Part II. Branch-Circuit Load Calculations ..............................94220.12 General Lighting........................................................94220.14 Other Loads—All Occupancies ................................95220.18 Maximum Load on a Branch Circuit ........................99

Part III. Feeder and Service Calculations............................100220.40 General ....................................................................100220.42 General Lighting Demand Factors ..........................100220.43 Commercial—Show Window and Track

Lighting Load ..........................................................100220.44 Commercial—Receptacle Load ..............................101220.50 Motor Load..............................................................101220.51 Fixed Electric Space-Heating Load.........................101220.52 Dwelling Unit—Small-Appliance and Laundry

Load.........................................................................102220.53 Dwelling Unit—Appliance Load ............................102220.54 Dwelling Unit—Electric Clothes Dryer Load.........102220.55 Dwelling Unit—Electric Ranges and Cooking

Appliances ...............................................................103220.56 Commercial—Kitchen Equipment Load.................104220.60 Noncoincident Loads...............................................104220.61 Feeder/Service Neutral Unbalanced Load...............104

Part IV. Optional Calculations for Computing Feeder and Service Loads ................................................................107220.82 Dwelling Unit—Optional Load Calculation ...........107

220.84 Multifamily—Optional Load Calculation ...............108220.85 Optional Calculation—Two Dwelling Units...........108

Article 220 Questions..............................................109

Article 225 Outside Wiring ...............................................111

Part I General Requirements................................................111225.1 Scope .......................................................................111225.2 Other Articles ..........................................................111225.6 Minimum Size Conductors......................................112225.7 Luminaires Installed Outdoors ................................112225.15 Supports Over Buildings .........................................112225.16 Attachment ..............................................................112225.17 Masts as Support .....................................................113225.18 Clearances................................................................113225.19 Clearances from Buildings ......................................113225.22 Raceways on Exterior Surfaces of Buildings

or Other Structures ..................................................114225.26 Trees for Conductor Support...................................115

Part II. More Than One Building or Structure .....................115225.30 Number of Supplies.................................................115225.31 Disconnecting Means ..............................................115225.32 Disconnect Location................................................116225.33 Maximum Number of Disconnects .........................117225.34 Grouping of Disconnects.........................................117225.35 Access to Occupants................................................117225.36 Identified as Suitable for Service Equipment .........117225.37 Identification of Multiple Supplies .........................117225.38 Disconnect Construction .........................................117225.39 Rating of Disconnecting Means ..............................117


Article 230 Services ..........................................................119

Part I. General .......................................................................120230.1 Scope .......................................................................120230.2 Number of Services .................................................120230.3 Pass Through a Building or Structure .....................121230.6 Conductors Considered Outside a Building............121230.7 Service Conductors Separate from Other

Conductors...............................................................121230.8 Raceway Seals .........................................................122230.9 Clearance from Building Openings.........................122230.10 Vegetation as Support ..............................................123

Part II. Overhead Service-Drop Conductors........................123230.23 Size and Rating........................................................123230.24 Clearances................................................................123230.26 Point of Attachment.................................................124230.27 Means of Attachment ..............................................125230.28 Service Masts Used as Supports .............................125

Part III. Underground Service-Lateral Conductors .............125230.31 Size and Rating........................................................125230.32 Protection Against Damage.....................................125

Part IV. Service–Entrance Conductors.................................125230.40 Number of Service-Entrance Conductor Sets .........125230.42 Size and Rating........................................................126230.43 Wiring Methods.......................................................126230.44 Cable Trays..............................................................126230.46 Spliced Conductors..................................................127230.50 Protection Against Physical Damage—

Aboveground ...........................................................127230.51 Service Cable Supports ...........................................127230.54 Connections at Weatherheads..................................127230.56 High-Leg Identification ...........................................128

Part V. Service Equipment—General...................................128230.66 Identified as Suitable for Service Equipment .........128

Part VI. Service Equipment—Disconnecting Means..........129230.70 General ....................................................................129230.71 Number of Disconnects ...........................................130230.72 Grouping of Disconnects.........................................130230.76 Manual or Power Operated .....................................131230.79 Rating of Disconnect ...............................................131230.82 Equipment Connected to the Supply Side of

the Service Disconnect...........................................131

Part VII. Service Equipment Overcurrent Protection ..........132230.90 Overload Protection Required .................................132230.95 Ground-Fault Protection of Equipment...................133


Article 240 Overcurrent Protection.................................135

Part I. General .......................................................................136240.1 Scope .......................................................................136240.2 Definitions ...............................................................136240.3 Protection of Equipment..........................................137240.4 Protection of Conductors.........................................137240.5 Protection of Flexible Cords and Fixture Wires......140240.6 Standard Ampere Ratings........................................140240.10 Supplementary Overcurrent Protection ...................140240.13 Ground-Fault Protection of Equipment...................141

Part II. Location .....................................................................141240.20 Ungrounded Conductors..........................................141240.21 Overcurrent Protection Location in Circuit.............142240.24 Location of Overcurrent Protection Devices...........147

Part III. Enclosures ................................................................148240.32 Damp or Wet Locations...........................................148240.33 Vertical Position ......................................................149

Part V. Plug Fuses, Fuseholders, and Adapters ..................149240.51 Edison-Base Fuse ....................................................149240.53 Type S Fuses............................................................149240.54 Type S Fuses, Adapters, and Fuseholders ...............149

Part VI. Cartridge Fuses and Fuseholders ..........................149240.60 General ....................................................................150240.61 Classification ...........................................................150

Part VII. Circuit Breakers ......................................................150240.80 Method of Operation ...............................................150240.81 Indicating.................................................................151240.83 Markings..................................................................151240.85 Applications.............................................................152


Article 250 Grounding and Bonding ...............................155

Part I. General .......................................................................155250.1 Scope .......................................................................155250.2 Definitions ...............................................................156250.4 General Requirements for Grounding and

Bonding ...................................................................160250.6 Objectionable Current .............................................164250.8 Termination of Grounding and Bonding

Conductors...............................................................168250.10 Protection of Fittings ...............................................168250.12 Clean Surface ..........................................................168

Part II. System Grounding and Bonding ..............................168250.20 Systems Required to be Grounded and Bonded .....168250.24 Grounding and Bonding at Service Equipment ......170250.28 Main Bonding Jumper and System Bonding

Jumper .....................................................................175250.30 Grounding and Bonding of Separately

Derived AC Systems................................................176250.32 Buildings or Structures Supplied by a Feeder or

Branch Circuit .........................................................181250.34 Generators—Portable and Vehicle-Mounted...........183250.36 High-Impedance Grounded Neutral Systems..........184

Part III. Grounding Electrode System and GroundingElectrode Conductor .............................................................184250.50 Grounding Electrode System ..................................185250.52 Grounding (Earthing) Electrodes ............................185250.53 Installation of Grounding Electrode System...........188250.54 Supplementary Electrodes .......................................190250.56 Resistance of Ground Rod Electrode ......................190250.58 Common Grounding (Earthing) Electrode..............192250.60 Lightning Protection System Grounding

(Earthing) Electrode ................................................192250.62 Grounding Electrode Conductor—Material............193250.64 Grounding Electrode Conductor Installation ..........193

viii

Table of Contents Understanding the National Electrical Code, Volume 1

ix

250.66 Grounding Electrode Conductor—Size ..................195250.68 Grounding Electrode Conductor Termination.........196250.70 Grounding Electrode Conductor Termination

Fitting ......................................................................197

Part IV. Grounding (Bonding) of Enclosure, Raceway,and Service Cable................................................................197250.80 Service Enclosures ..................................................197250.86 Other Enclosures .....................................................197

Part V. Bonding ......................................................................198250.92 Service Bonding ......................................................198250.94 Grounding (Bonding) of Communications

Systems....................................................................200250.96 Bonding Other Enclosures ......................................201250.97 Bonding 277V/480V ...............................................202250.100 Bonding—Hazardous (Classified) Locations..........203250.102 Bonding Jumper ......................................................203250.104 Bonding of Piping Systems and Exposed

Structural Metal .......................................................205250.106 Lightning Protection System...................................208

Part VI. Equipment Grounding (Bonding) and EquipmentGrounding (Bonding) Conductors.........................................209250.110 Fixed Equipment Connected by Permanent

Wiring Methods—General ......................................209250.112 Fixed Equipment Connected by Permanent

Wiring Methods—Specific......................................209250.114 Equipment Connected by Cord and Plug................209250.118 Types of Equipment Grounding (Bonding)

Conductors...............................................................210250.119 Identification of Equipment Grounding

(Bonding) Conductor...............................................212250.122 Sizing Equipment Grounding (Bonding)

Conductor ................................................................213250.126 Identification of Wiring Device Terminals..............215

Part VII. Methods of Equipment Grounding (Bonding) .......215250.130 Equipment Grounding (Bonding) Conductor

Connections .............................................................215250.134 Grounding (Bonding)—Fixed Equipment...............216250.138 Grounding (Bonding)—Cord-and-Plug

Connected Equipment .............................................217250.140 Grounding (Bonding)—Ranges, Ovens, and

Clothes Dryers .........................................................217250.142 Use of Grounded Neutral Conductor for

Equipment Grounding (Bonding)............................218250.146 Connecting Receptacle Grounding Terminal

to Box ......................................................................219250.148 Continuity and Attachment of Equipment

Grounding (Bonding) Conductors to Boxes ...........221Article 250 Questions..............................................223

Article 280 Surge Arresters .............................................227

Part I. General .......................................................................227280.1 Scope .......................................................................227280.2 Definition.................................................................227280.3 Number Required ....................................................227280.4 Surge Arrester Selection..........................................227

Part II. Installation.................................................................228280.11 Location...................................................................228280.12 Routing of Conductors ............................................228

Part III. Connecting Surge Arresters ....................................228280.21 Installed at Services of Less Than 1,000V..............228280.22 Installed on the Load Side of Services of

Less Than 1,000V....................................................228Article 280 Questions..............................................229

Article 285 Transient Voltage Surge Suppressors(TVSSs) .................................................................................231

Part I. General .......................................................................231285.1 Scope .......................................................................231285.2 Definition.................................................................231285.3 Uses Not Permitted..................................................231285.4 Number Required ....................................................231285.5 Listing......................................................................232285.6 Short-Circuit Current Rating...................................232

Part II. Installation.................................................................232285.11 Location...................................................................232285.12 Routing of Conductors ............................................232

Part III. Connecting Transient Voltage Surge Suppressors ..........................................................................232285.21 Connection...............................................................232


Chapter 3—Wiring Methods and Materials ...........235

Article 300 Wiring Methods .............................................239

Part I. General Requirements...............................................239300.1 Scope .......................................................................239300.3 Conductors...............................................................240300.4 Protection Against Physical Damage ......................241300.5 Underground Installations .......................................244300.6 Protection Against Corrosion and Deterioration .....247300.7 Raceways Exposed to Different Temperatures........248300.8 Not Permitted in Raceways .....................................249300.10 Electrical Continuity................................................249300.11 Securing and Supporting .........................................250


300.12 Mechanical Continuity ............................................251300.13 Splices and Pigtails..................................................252300.14 Length of Free Conductors......................................253300.15 Boxes or Conduit Bodies.........................................254300.17 Raceway Sizing .......................................................255300.18 Inserting Conductors in Raceways ..........................257300.19 Supporting Conductors in Vertical Raceways .........257300.20 Induced Currents in Metal Parts..............................257300.21 Spread of Fire or Products of Combustion .............258300.22 Ducts, Plenums, and Air-Handling Spaces .............259300.23 Panels Designed to Allow Access ...........................260


Article 310 Conductors For General Wiring ..................265310.1 Scope .......................................................................265310.2 Conductors...............................................................265310.3 Stranded Conductors ...............................................265310.4 Conductors in Parallel .............................................266310.5 Minimum Size Conductors......................................267310.8 Location...................................................................267310.9 Corrosive Conditions...............................................268310.10 Insulation Temperature Limitation ..........................268310.12 Conductor Identification..........................................268310.13 Conductor Construction ..........................................269310.15 Conductor Ampacity................................................269


Article 312 Cabinets, Cutout Boxes, and Meter Socket Enclosures..............................................................277312.1 Scope .......................................................................277

Part I. Installation..................................................................277312.2 Damp, Wet, or Hazardous (Classified) Locations...277312.3 Installed in Walls .....................................................278312.4 Repairing Gaps Around Plaster, Drywall, or

Plasterboard Edges .................................................278312.5 Enclosures................................................................278312.8 Used for Raceway and Splices ................................279


Article 314 Outlet, Device, Pull and Junction Boxes, Conduit Bodies, and Handhole Enclosures .....281

Part I. Scope and General ....................................................281314.1 Scope .......................................................................281314.3 Nonmetallic Boxes ..................................................281314.4 Metal Boxes.............................................................281314.5 Short-Radius Conduit Bodies..................................282

Part II. Installation.................................................................282314.15 Damp, Wet, or Hazardous (Classified) Locations...282

314.16 Number of 6 AWG and Smaller Conductors in Boxes and Conduit Bodies..................................282

314.17 Conductors That Enter Boxes or Conduit Bodies ......................................................................285

314.20 Boxes Recessed in Walls or Ceilings ......................285314.21 Repairing Gaps Around Boxes................................286314.22 Surface Extensions ..................................................286314.23 Support of Boxes and Conduit Bodies....................287314.25 Covers and Canopies ...............................................288314.27 Outlet Box ...............................................................288314.28 Boxes and Conduit Bodies for Conductors

4 AWG and Larger ..................................................289314.29 Wiring to be Accessible...........................................291314.30 Handhole Enclosures ...............................................291


Article 320 Armored Cable (Type AC).............................295

Part I. General .......................................................................295320.1 Scope .......................................................................295320.2 Definition.................................................................295

Part II. Installation.................................................................295320.10 Uses Permitted.........................................................295320.12 Uses Not Permitted..................................................295320.15 Exposed Work..........................................................296320.17 Through or Parallel to Framing Members...............296320.23 In Accessible Attics or Roof Spaces .......................296320.24 Bends .......................................................................297320.30 Secured and Supported............................................297320.40 Boxes and Fittings ...................................................298320.80 Conductor Ampacities .............................................298

Part III. Construction Specifications ....................................299320.100 Construction ............................................................299320.108 Equipment Grounding (Bonding)............................299


Article 330 Metal-Clad Cable (Type MC) .......................301


Part II. Installation.................................................................301330.10 Uses Permitted.........................................................301330.12 Uses Not Permitted..................................................302330.17 Through or Parallel to Framing Members...............302330.23 In Accessible Attics or Roof Spaces .......................302330.24 Bends .......................................................................303

Part II. Installation.................................................................303330.30 Secured and Supported............................................303

x


xi

330.40 Fittings.....................................................................304330.80 Conductor Ampacities .............................................304

Part III. Construction Specifications ....................................304330.108 Equipment Grounding (Bonding)............................304


Article 334 Nonmetallic-Sheathed Cable (Types NM and NMC) .........................................................307

Part I. General .......................................................................307334.1 Scope .......................................................................307334.2 Definition.................................................................307334.6 Listed .......................................................................307

Part II. Installation.................................................................307334.10 Uses Permitted.........................................................307334.12 Uses Not Permitted..................................................308334.15 Exposed ...................................................................309334.17 Through or Parallel to Framing Members...............309334.23 Attics and Roof Spaces ...........................................310334.24 Bends .......................................................................311334.30 Secured or Supported ..............................................311334.80 Conductor Ampacity................................................312

Part III. Construction Specifications ....................................313334.100 Construction ............................................................313334.104 Conductors...............................................................313334.108 Equipment Grounding .............................................313334.112 Insulation .................................................................313


Article 336 Power and Control Tray Cable (Type TC)...............................................................................315


Part II. Installation.................................................................315336.10 Uses Permitted.........................................................315336.12 Uses Not Permitted..................................................315


Article 338 Service-Entrance Cables (Types SE and USE)............................................................317


Part II. Installation.................................................................317338.10 Uses Permitted.........................................................317338.24 Bends .......................................................................318


Article 340 Underground Feeder and Branch-Circuit Cable (Type UF) .......................................321

Part I. General .......................................................................321340.1 Scope .......................................................................321340.2 Definition.................................................................321340.6 Listing Requirements ..............................................321

Part II. Installation.................................................................321340.10 Uses Permitted.........................................................321340.12 Uses Not Permitted..................................................321340.24 Bends .......................................................................322340.80 Ampacity .................................................................322340.112 Insulation .................................................................322


Article 342 Intermediate Metal Conduit (Type IMC) ...325


Part II. Installation.................................................................325342.10 Uses Permitted.........................................................325342.14 Dissimilar Metals ....................................................326342.20 Trade Size ................................................................326342.22 Number of Conductors ............................................326342.24 Bends .......................................................................326342.26 Number of Bends (360°) .........................................326342.28 Reaming...................................................................326342.30 Secured and Supported............................................326342.42 Couplings and Connectors ......................................328342.46 Bushings ..................................................................328


Article 344 Rigid Metal Conduit (Type RMC) ................331


Part II. Installation.................................................................331344.10 Uses Permitted.........................................................331344.14 Dissimilar Metals ....................................................331344.20 Trade Size ................................................................332344.22 Number of Conductors ............................................332344.24 Bends .......................................................................332344.26 Number of Bends (360°) .........................................332344.28 Reaming...................................................................332344.30 Secured and Supported............................................332344.42 Couplings and Connectors ......................................333


344.46 Bushings ..................................................................334Article 344 Questions..............................................335

Article 348 Flexible Metal Conduit (Type FMC)............337


Part II. Installation.................................................................337348.10 Uses Permitted.........................................................337348.12 Uses Not Permitted..................................................337348.20 Trade Size ................................................................337348.22 Number of Conductors ............................................338348.24 Bends .......................................................................338348.26 Number of Bends (360°) .........................................338348.28 Trimming .................................................................338348.30 Secured and Supported............................................338348.42 Fittings.....................................................................339348.60 Bonding ...................................................................339


Article 350 Liquidtight Flexible Metal Conduit (Type LFMC) .........................................................................341

Part I. General .......................................................................341350.1 Scope .......................................................................341350.2 Definition.................................................................341350.6 Listing Requirement ................................................341

Part II. Installation.................................................................341350.10 Uses Permitted.........................................................341350.12 Uses Not Permitted..................................................341350.20 Trade Size ................................................................341350.22 Number of Conductors ............................................342350.24 Bends .......................................................................342350.26 Number of Bends (360°) .........................................342350.30 Secured and Supported............................................342350.42 Fittings.....................................................................343350.60 Bonding ...................................................................343


Article 352 Rigid Nonmetallic Conduit (Type RNC) .....345


Part II. Installation.................................................................345352.10 Uses Permitted.........................................................345352.12 Uses Not Permitted..................................................346352.20 Trade Size ................................................................346

352.22 Number of Conductors ............................................347352.24 Bends .......................................................................347352.26 Number of Bends (360°) .........................................347352.28 Trimming .................................................................347352.30 Secured and Supported............................................347352.44 Expansion Fittings...................................................348352.46 Bushings ..................................................................348352.48 Joints........................................................................348352.60 Grounding (Bonding) ..............................................349


Article 353 High-Density Polyethylene Conduit (Type HDPE) ..........................................................351


Part II. Installation.................................................................351353.10 Uses Permitted.........................................................351353.12 Uses Not Permitted..................................................351353.20 Trade Size ................................................................352353.22 Number of Conductors ............................................352353.24 Bends—How Made .................................................352353.26 Bends—Number in One Run ..................................352353.28 Trimming .................................................................352353.46 Bushings ..................................................................352353.48 Joints........................................................................352353.56 Splices and Taps ......................................................352353.60 Grounding (Bonding) ..............................................352


Article 354 Nonmetallic Underground Conduit with Conductors (Type NUCC)..........................................355


Part II. Installation.................................................................355354.10 Uses Permitted.........................................................355354.12 Uses Not Permitted..................................................355354.20 Trade Size ................................................................356354.24 Bends .......................................................................356354.26 Number of Bends (360º) .........................................356354.28 Trimming .................................................................356354.46 Bushings ..................................................................356354.48 Joints........................................................................356354.50 Conductor Terminations ..........................................356


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xiii

Article 356 Liquidtight Flexible Nonmetallic Conduit (Type LFNC) ..........................................................359


Part II. Installation.................................................................359356.10 Uses Permitted.........................................................359356.12 Uses Not Permitted..................................................359356.20 Trade Size ................................................................359356.22 Number of Conductors ............................................360356.24 Bends .......................................................................360356.26 Number of Bends (360°) .........................................360356.30 Secured and Supported............................................360356.42 Fittings.....................................................................360356.60 Grounding (Bonding) ..............................................360


Article 358 Electrical Metallic Tubing (Type EMT).......363


Part II. Installation.................................................................363358.10 Uses Permitted.........................................................363358.12 Uses Not Permitted..................................................364358.20 Trade Size ................................................................364358.22 Number of Conductors ............................................364358.24 Bends .......................................................................364358.26 Number of Bends (360°) .........................................364358.28 Reaming and Threading ..........................................365358.30 Secured and Supported............................................365358.42 Coupling and Connectors ........................................365


Article 362 Electrical Nonmetallic Tubing (Type ENT) ............................................................................367


Part II. Installation.................................................................367362.10 Uses Permitted.........................................................367362.12 Uses Not Permitted..................................................369362.20 Trade Sizes ..............................................................369362.22 Number of Conductors ............................................369362.24 Bends .......................................................................370362.26 Number of Bends (360°) .........................................370

362.28 Trimming .................................................................370362.30 Secured and Supported............................................370362.46 Bushings ..................................................................370362.48 Joints........................................................................370362.60 Grounding (Bonding) ..............................................370


Article 376 Metal Wireways .............................................373


Part II. Installation.................................................................373376.10 Uses Permitted.........................................................373376.12 Uses Not Permitted..................................................373376.21 Conductor—Maximum Size....................................373376.22 Number of Conductors ............................................373376.23 Wireway Sizing .......................................................374376.30 Supports ...................................................................374376.56 Splices and Taps ......................................................375


Article 378 Nonmetallic Wireways .................................377


Part II. Installation.................................................................377378.10 Uses Permitted.........................................................377378.12 Uses Not Permitted..................................................377378.21 Conductor—Maximum Size....................................377378.22 Number of Conductors ............................................377378.23 Wireway Sizing .......................................................378378.30 Supports ...................................................................378378.44 Expansion Fittings...................................................378378.56 Splices and Taps ......................................................378378.60 Grounding (Bonding) ..............................................378


Article 380 Multioutlet Assembly....................................381380.1 Scope .......................................................................381380.2 Uses .........................................................................381380.3 Through Partitions ...................................................381


Article 384 Strut-Type Channel Raceways ...................383



Part II. Installation.................................................................383384.10 Uses Permitted.........................................................383384.12 Uses Not Permitted..................................................383384.21 Conductor—Maximum Size....................................384384.22 Number of Conductors ............................................384384.30 Securing and Supporting .........................................384384.56 Splices and Taps ......................................................384384.60 Grounding (Bonding) ..............................................384


Article 386 Surface Metal Raceways ............................387


Part II. Installation.................................................................387386.10 Uses Permitted.........................................................387386.12 Uses Not Permitted..................................................388386.21 Size of Conductors ..................................................388386.22 Number of Conductors ............................................388386.30 Securing and Supporting .........................................388386.56 Splices and Taps ......................................................388386.60 Grounding (Bonding) ..............................................388386.70 Separate Compartments...........................................388


Article 388 Surface Nonmetallic Raceways .................391


Part II. Installation.................................................................391388.10 Uses Permitted.........................................................391388.12 Uses Not Permitted..................................................391388.21 Size of Conductors ..................................................391388.22 Number of Conductors ............................................391388.56 Splices and Taps ......................................................392388.60 Grounding (Bonding) ..............................................392388.70 Separate Compartments...........................................392


Article 392 Cable Trays .....................................................395392.1 Scope .......................................................................395392.2 Definition.................................................................395392.3 Uses Permitted.........................................................395392.4 Uses Not Permitted..................................................396392.6 Installation ...............................................................396392.7 Grounding (Bonding) ..............................................396

392.8 Cable Installation.....................................................397Article 392 Questions..............................................398

Chapter 4—Equipment for General Use ..................399

Article 400 Flexible Cords and Flexible Cables ...........401400.1 Scope .......................................................................401400.3 Suitability ................................................................401400.4 Types of Flexible Cords and Flexible Cables .........401400.5 Ampacity of Flexible Cords and Flexible Cables ...401400.7 Uses Permitted.........................................................402400.8 Uses Not Permitted..................................................403400.10 Pull at Joints and Terminals ....................................404400.13 Overcurrent Protection ............................................404400.14 Protection from Damage .........................................404


Article 402 Fixture Wires ..................................................402402.1 Scope .......................................................................407402.3 Types........................................................................407402.5 Allowable Ampacity of Fixture Wires ....................407402.6 Minimum Size .........................................................407402.7 Raceway Size...........................................................407402.8 Grounded Neutral Conductor ..................................408402.10 Uses Permitted.........................................................408402.11 Uses Not Permitted..................................................408402.12 Overcurrent Protection ............................................408


Article 404 Switches .........................................................411404.1 Scope .......................................................................411404.2 Switch Connections.................................................411404.3 Switch Enclosures ...................................................412404.4 Wet Locations..........................................................412404.6 Position of Knife Switches......................................413404.7 Indicating.................................................................413404.8 Accessibility and Grouping.....................................414404.9 Switch Cover Plates (Faceplate)..............................415404.10 Mounting Snap Switches.........................................415404.11 Circuit Breakers Used as Switches .........................415404.12 Grounding (Bonding) Metal Enclosures .................415404.14 Rating and Use of Snap Switches ...........................416404.15 Switch Marking .......................................................416


Article 406 Receptacles, Cord Connectors, andAttachment Plugs Caps.....................................................419406.1 Scope .......................................................................419

xiv


xv

406.2 Receptacle Rating and Type ....................................419406.3 General Installation Requirements ..........................420406.4 Receptacle Mounting...............................................421406.5 Receptacle Faceplates..............................................423406.6 Attachment Plugs, Cord Connectors, and

Flanged Surface Devices .........................................423406.8 Receptacles in Damp or Wet Locations ..................424406.10 Connecting Receptacle Grounding Terminal

to Box ......................................................................425Article 406 Questions..............................................426

Article 408 Switchboards and Panelboards .................427

Part I. General .......................................................................427408.1 Scope .......................................................................427408.3 Arrangement of Busbars and Conductors ...............427408.4 Circuit Directory or Circuit Identification ..............428408.5 Clearance for Conductor Entering Bus

Enclosures................................................................428408.7 Unused Openings ....................................................429

Part III. Panelboards .............................................................429408.34 Classification of Panelboards ..................................429408.35 Number of Overcurrent Protection Devices............429408.36 Overcurrent Protection of Panelboard.....................429408.37 Panelboards in Damp or Wet Locations..................431408.40 Grounding (Bonding) of Panelboards .....................431408.41 Grounded Neutral Conductor Terminations ............432


Article 410 Luminaires, Lampholders, and Lamps .....435

Part I. General .......................................................................435410.1 Scope .......................................................................435

Part II. Luminaire Locations .................................................435410.4 Luminaires in Specific Locations............................435410.8 Clothes Closets ........................................................437

Part III. Luminaire Outlet Boxes and Covers .......................438410.12 Outlet Boxes to be Covered ....................................438410.14 Connection of Electric-Discharge Luminaires ........438

Part IV. Luminaire Supports .................................................439410.15 Supports ...................................................................439410.16 Means of Support ....................................................440

Part V. Grounding (Bonding) .................................................442410.18 Exposed Luminaire Parts .......................................442

Part VI. Wiring of Luminaires ...............................................442410.23 Polarization of Luminaires ......................................442410.30 Cord-Connected Luminaires ...................................442410.31 Luminaires Used as a Raceway...............................443

410.32 Wiring Luminaires Connected Together .................443410.33 Branch-Circuit Conductors and Ballast ..................443

Part VIII. Lampholders ..........................................................443410.47 Screw-Shell Lampholder .........................................443

Part XI. Recessed Luminaires ..............................................443410.65 Thermally Protected ................................................443410.66 Recessed Luminaire Clearances..............................444410.67 Wiring ......................................................................444

Part XIII. Electric-Discharge Lighting ..................................444410.73 General ....................................................................444410.76 Luminaire Mounting................................................445

Part XV. Track Lighting..........................................................445410.100 Definition.................................................................445410.101 Installation ...............................................................445410.104 Fastening..................................................................446

Part XVI. Decorative Lighting and Similar Accessories ....446410.110 Listing of Decorative Lighting ................................446


Article 411 Lighting Systems Operating at 30V or Less ..........................................................................449411.1 Scope .......................................................................449411.2 Definition.................................................................449411.3 Listing Required ......................................................449411.4 Locations Not Permitted..........................................449411.5 Secondary Circuits ..................................................450


Article 422 Appliances ......................................................453

Part I. General .......................................................................453422.1 Scope .......................................................................453422.3 Other Articles ..........................................................453

Part II. Branch-Circuit Requirements ..................................454422.10 Branch-Circuit Rating .............................................454422.11 Overcurrent Protection ............................................454422.12 Fossil Fuel Heating Equipment (Furnaces).............455422.13 Storage Water Heaters .............................................455422.15 Central Vacuum .......................................................455422.16 Flexible Cords .........................................................456422.18 Support of Ceiling-Suspended (Paddle) Fans .........457

Part III. Disconnect................................................................457422.31 Permanently Connected Appliance Disconnect ......457422.33 Cord-and-Plug Connected Appliance Disconnect...457422.34 Unit Switch as Disconnect ......................................458422.51 Cord-and-Plug Connected Vending Machines ........458



Article 424 Fixed Electric Space-Heating Equipment............................................................................461

Part I. General .......................................................................461424.1 Scope .......................................................................461424.3 Branch Circuits........................................................461424.9 Permanently Installed Electric Baseboard

Heaters with Receptacles ........................................462

Part III. Electric Space-Heating Equipment ........................462424.19 Disconnecting Means ..............................................462

Part V. Electric Space-Heating Cables.................................462424.44 Installation of Cables in Concrete or Poured

Masonry Floors........................................................462

Part VI. Duct Heaters ............................................................462424.65 Disconnect for Electric Duct Heater Controller......462


Article 430 Motors, Motor Circuits, and Controllers............................................................................465

Part I. General .......................................................................465430.1 Scope .......................................................................465430.2 Definitions ...............................................................466430.6 Table FLC Versus Motor Nameplate Current

Rating ......................................................................466430.8 Marking on Controllers ...........................................467430.9 Motor Controller Terminal Requirements...............467430.14 Location of Motors..................................................468430.17 The Highest-Rated Motors ......................................468

Part II. Conductor Size ..........................................................468430.22 Single Motor—Conductor Size ...............................468430.24 Several Motors—Conductor Size............................469430.28 Motor Feeder Taps...................................................469

Part III. Overload Protection .................................................469430.31 Overload ..................................................................470430.32 Overload Sizing—Continuous-Duty Motors...........471430.36 Use of Fuses for Overload Protection .....................471430.37 Number of Overload Devices..................................472

Part IV. Branch-Circuit Short-Circuit and Ground-FaultProtection ..............................................................................472430.51 General ....................................................................472430.52 Branch-Circuit Short-Circuit and Ground-Fault

Protection.................................................................472430.55 Single Overcurrent Protective Device .....................473

Part V. Feeder Short-Circuit and Ground-Fault Protection ..............................................................................473430.62 Feeder Protection.....................................................473

Part VI. Motor Control Circuits .............................................474430.72 Overcurrent Protection for Control Circuits ...........474430.74 Disconnect for Control Circuit................................474

Part VII. Motor Controllers ....................................................475430.83 Controller Rating.....................................................475430.84 Need Not Open All Conductors of the Circuit........475430.87 Controller for Each Motor.......................................475430.91 Motor Controller Enclosure Types ..........................476

Part IX. Disconnecting Means..............................................476430.102 Disconnect Requirement .........................................476430.103 Disconnect Opens All Conductors ..........................477430.104 Marking and Mounting............................................477430.107 Readily Accessible ..................................................477430.109 Disconnecting Means Rating ..................................477430.111 Combination Controller-Disconnect .......................477

Part X. Adjustable-Speed Drive Systems ............................478430.120 General ....................................................................478430.122 Conductors—Minimum Size and Ampacity ...........478430.124 Overload Protection.................................................478430.128 Disconnecting Means ..............................................478

Part XIV. Tables......................................................................478Table 430.248 Full-Load Current, Single-Phase Motors .....478Table 430.250 Full-Load Current, Three-Phase Motors ......478Table 430.251 Locked-Rotor Currents .................................478


Article 440 Air-Conditioning and RefrigerationEquipment............................................................................481

Part I. General .......................................................................481440.1 Scope .......................................................................481440.2 Definitions ...............................................................481440.3 Other Articles ..........................................................481440.4 Marking on Hermetic Refrigerant

Motor-Compressors and Equipment .......................482440.6 Ampacity and Rating...............................................482

Part II. Disconnecting Means ...............................................482440.14 Location...................................................................482

Part III. Circuit Protection .....................................................483440.21 General ....................................................................483440.22 Short-Circuit and Ground-Fault Protection

Device Size..............................................................483

Part IV. Conductor Sizing ......................................................484440.32 Conductor Size—One Motor-Compressor .............484440.33 Conductor Size—Several Motor-Compressors .......485

Part VII. Room Air Conditioners............................................485440.62 Branch-Circuit Requirements..................................485

xvi


xvii

440.63 Disconnecting Means ..............................................485440.64 Supply Cord.............................................................485440.65 Leakage Current Detection and Interruption, and

Arc-Fault Circuit Interrupter ...................................485Article 440 Questions..............................................486

Article 445 Generators ......................................................487445.1 Scope .......................................................................487445.11 Marking ...................................................................487445.12 Overcurrent Protection ............................................487445.13 Ampacity of Conductors .........................................487445.18 Disconnecting Means ..............................................488


Article 450 Transformers and Transformer Vaults ....................................................................................491

Part I. General .......................................................................491450.1 Scope .......................................................................491450.3 Overcurrent Protection ............................................491450.9 Ventilation................................................................493450.11 Marking ...................................................................493450.13 Transformer Accessibility .......................................493

Part III. Transformer Vaults...................................................493450.41 Location...................................................................493450.42 Walls, Roofs, and Floors .........................................494450.43 Doorways.................................................................494450.45 Ventilation Openings ...............................................494450.47 Water Pipes and Accessories ...................................494450.48 Storage in Vaults......................................................494


Article 460 Capacitors.......................................................497460.1 Scope .......................................................................497460.2 Enclosing and Guarding ..........................................497

Part I. 600V, Nominal, and Under.........................................497460.8 Conductors...............................................................497460.9 Rating or Setting of Motor Overload Device..........497



vi

Article 90—Introduction ...................................................190.1 Purpose of the NEC .....................................................190.2 Scope of the NEC ........................................................290.3 Code Arrangement.......................................................490.4 Enforcement ................................................................590.5 Mandatory Requirements and Explanatory

Material........................................................................690.6 Formal Interpretations .................................................690.7 Examination of Equipment for Product Safety ...........690.9 Units of Measurement .................................................7

Article 90 Questions....................................................8

Chapter 1—General ............................................................9

Article 100 Definitions.........................................................11Article 100 Questions................................................29

Article 110 Requirements for Electrical Installations ...........................................................................31

Part I. General Requirements.................................................31110.1 Scope .........................................................................31110.2 Approval of Equipment .............................................31110.3 Examination, Identification, Installation, and

Use of Equipment......................................................31110.4 Voltages .....................................................................32110.5 Copper Conductors....................................................32110.6 Conductor Sizes.........................................................32110.7 Conductor Insulation .................................................33110.8 Suitable Wiring Methods...........................................33110.9 Interrupting Protection Rating...................................33110.10 Short-Circuit Current Rating.....................................34110.11 Deteriorating Agents..................................................35110.12 Mechanical Execution of Work .................................36110.13 Mounting and Cooling of Equipment .......................37110.14 Conductor Termination..............................................37110.15 High-Leg Conductor Identification ...........................41110.16 Flash Protection Warning ..........................................42110.21 Manufacturer’s Markings ..........................................42110.22 Identification of Disconnecting Means .....................43

Part II. 600V, Nominal or Less ................................................43110.26 Spaces About Electrical Equipment ..........................43110.27 Guarding ....................................................................48


Chapter 5—Special Occupancies ..............................501

Article 500—Hazardous (Classified) Locations...........503500.1 Scope—Articles 500 Through 504..........................503500.2 Definitions ...............................................................504500.3 Other Articles ..........................................................505500.4 General ....................................................................505500.5 Classifications of Locations ....................................505500.6 Material Groups.......................................................507500.7 Protection Techniques .............................................508500.8 Equipment................................................................509500.9 Specific Occupancies...............................................511


Article 501—Class I Hazardous (Classified) Locations ........................................................513

Part I. General .......................................................................513501.1 Scope .......................................................................513501.5 General ....................................................................513

Part II. Wiring ........................................................................513501.10 Wiring Methods.......................................................513501.15 Conduit and Cable Seals .........................................515501.20 Conductor Insulation ...............................................519501.30 Bonding ...................................................................519501.35 Surge Protection ......................................................520501.40 Multiwire Branch Circuits.......................................520

Part III. Equipment ................................................................520501.100 Transformers and Capacitors...................................520501.105 Meters, Instruments, and Relays .............................521501.115 Enclosures................................................................521501.120 Control Transformers and Relays............................521501.125 Motors and Generators ............................................521501.130 Luminaires ...............................................................522

vii


501.140 Flexible Cords .........................................................523501.145 Receptacles and Attachment Plugs..........................523501.150 Low-Voltage, Limited-Energy, and

Communications Systems .......................................523Article 501 Questions..............................................525

Article 502—Class II Hazardous (Classified) Locations ........................................................527


Part II. Wiring ........................................................................528502.10 Wiring Methods.......................................................528502.15 Seals.........................................................................529502.30 Bonding ...................................................................529502.35 Surge Protection ......................................................530502.40 Multiwire Branch Circuits.......................................530

Part III. Equipment ................................................................530502.115 Switches, Circuit Breakers, Motor Controllers,

and Fuses .................................................................530502.120 Control Transformers ..............................................531502.125 Motors and Generators ............................................531502.130 Luminaires...............................................................532502.140 Flexible Cords .........................................................532502.145 Receptacles and Attachment Plugs..........................532502.150 Low-Voltage, Limited-Energy, and

Communications Systems .......................................532Article 502 Questions..............................................534

Article 503—Class III Hazardous (Classified) Locations ........................................................535


Part II. Wiring ........................................................................535503.10 Wiring Methods.......................................................535503.30 Bonding ...................................................................535

Part III. Equipment ................................................................536503.115 Switches, Circuit Breakers, Motor Controllers,

and Fuses .................................................................536503.120 Control Transformers ..............................................536503.125 Motors and Generators ............................................536503.130 Luminaires ...............................................................536503.140 Flexible Cords .........................................................537503.145 Receptacles and Attachment Plugs..........................537503.150 Signaling, Alarm, Remote-Control, and

Loudspeaker Systems ..............................................537Article 503 Questions..............................................538

Article 504—Intrinsically Safe Systems .......................539504.1 Scope .......................................................................539504.2 Definitions ...............................................................539504.3 Application of Other Articles ..................................539504.4 Equipment Approval................................................539504.10 Equipment Installation ............................................539504.20 Wiring Methods.......................................................540504.30 Separation of Intrinsically Safe Circuits .................540504.50 Grounding (Earthing) ..............................................540504.60 Bonding ...................................................................540504.70 Sealing .....................................................................540504.80 Identification............................................................540


Article 511—Commercial Garages, Repair, and Storage .................................................................................543511.1 Scope .......................................................................543511.3 Classification of Hazardous Areas ..........................543511.4 Wiring and Equipment in Hazardous

(Classified) Locations..............................................545511.7 Wiring and Equipment Above Hazardous

(Classified) Locations..............................................546511.9 Seals.........................................................................546511.10 Special Equipment...................................................547511.12 GFCI-Protected Receptacles ...................................547


Article 513—Aircraft Hangars.........................................549513.1 Scope .......................................................................549513.3 Classification of Locations......................................549513.4 Wiring and Equipment in Class I Locations ...........549513.7 Wiring Not Within Class I Locations......................549513.8 Wiring in or Under Hangar Floor............................550513.9 Sealing .....................................................................550513.12 GFCI-Protected Receptacles ...................................550513.16 Bonding ...................................................................550


Article 514—Motor Fuel Dispensing Facilities............553514.1 Scope .......................................................................553514.2 Definition.................................................................553514.3 Classification of Locations......................................553514.4 Wiring and Equipment Within Class I Locations ...554514.7 Wiring and Equipment Above Class I Locations ....554514.8 Underground Wiring................................................555514.9 Raceway Seal...........................................................555514.11 Emergency Dispenser Disconnects .........................556514.13 Maintenance and Service of Dispensing

Equipment................................................................556

viii

514.16 Grounding (Bonding) ..............................................557Article 514 Questions..............................................558

Article 517—Health Care Facilities ...............................559

Part I. General .......................................................................559517.1 Scope .......................................................................559517.2 Definitions ...............................................................559

Part II. Wiring and Protection...............................................560517.10 Applicability ............................................................560517.12 Wiring Methods.......................................................560517.13 Grounding (Bonding) Equipment in Patient

Care Areas ...............................................................560517.16 Isolated Ground Receptacles ...................................562517.18 General Care Areas..................................................562517.30 Essential Electrical Systems for Hospitals..............563


Article 518—Assembly Occupancies ............................567518.1 Scope .......................................................................567518.2 General Classifications............................................567518.3 Other Articles ..........................................................567518.4 Wiring Methods.......................................................567


Article 525—Carnivals, Circuses, Fairs, and Similar Events .....................................................................571

Part I. General Requirements...............................................571525.1 Scope .......................................................................571525.3 Other Articles ..........................................................571525.5 Overhead Conductor Clearances .............................571525.6 Protection of Electrical Equipment .........................572

Part II. Power Sources..........................................................572525.10 Services....................................................................572525.11 Multiple Sources of Supply.....................................572525.20 Wiring Methods.......................................................572525.21 Rides, Tents, and Concessions ................................573525.22 Outdoor Portable Distribution or

Termination Boxes...................................................573525.23 GFCI-Protected Receptacles and Equipment..........573

Part IV. Grounding and Bonding ..........................................574525.30 Equipment Bonding.................................................574525.31 Equipment Grounding (Bonding)............................574525.32 Grounding (Bonding) Conductor Continuity

Assurance ................................................................574Article 525 Questions..............................................575

Article 547—Agricultural Buildings ...............................577547.1 Scope .......................................................................577547.2 Definitions ...............................................................577547.5 Wiring Methods.......................................................578547.10 Equipotential Planes and Bonding of

Equipotential Planes ................................................579Article 547 Questions..............................................580

Article 550—Mobile Homes, Manufactured Homes, and Mobile Home Parks ....................................581

Part I. General .......................................................................581550.1 Scope .......................................................................581550.2 Definitions ...............................................................581550.4 General Requirements .............................................582550.13 Receptacle Outlets ...................................................582550.25 Arc-Fault Circuit-Interrupter (AFCI) Protection.....583

Part III. Services and Feeders ..............................................583550.30 Distribution Systems ...............................................583550.31 Allowable Demand Factors .....................................583550.32 Disconnect ...............................................................584550.33 Feeder ......................................................................585


Article 551—Recreational Vehicles and Recreational Vehicle Parks ..............................................587

Part I. General .......................................................................587551.1 Scope .......................................................................587551.2 Definitions ...............................................................587551.3 Other Articles ..........................................................587

Part VI. Recreational Vehicle Parks .....................................587551.71 Type of Receptacles Required.................................587551.73 Calculated Load.......................................................587551.79 Clearance for Overhead Conductors .......................588


Article 555—Marinas and Boatyards ............................591555.1 Scope .......................................................................591555.2 Definitions ...............................................................591555.5 Transformers............................................................592555.9 Electrical Connections.............................................592555.12 Load Calculations for Service and

Feeder Conductors...................................................592555.17 Boat Receptacle Disconnecting Means ...................592555.19 Receptacles ..............................................................593555.21 Motor Fuel Dispensing Stations..............................594555.22 Repair Facilities.......................................................594



ix

Article 590—Temporary Installations............................597590.1 Scope .......................................................................597590.2 All Installations .......................................................597590.3 Time Constraints .....................................................597590.4 General ....................................................................598590.6 Ground-Fault Protection for Personnel ...................599


Chapter 6—Special Equipment ..................................603

Article 600—Electric Signs and Outline Lighting .......605

Part I. General .......................................................................605600.1 Scope .......................................................................605600.2 Definitions ...............................................................605600.3 Listing......................................................................605600.4 Markings..................................................................606600.5 Branch Circuits........................................................606600.6 Disconnects..............................................................606600.9 Location...................................................................606600.10 Portable or Mobile Signs.........................................607600.21 Ballasts, Transformers, and Electronic

Power Supplies ........................................................607Article 600 Questions..............................................609

Article 604—Manufactured Wiring Systems ...............611604.1 Scope .......................................................................611604.2 Definition.................................................................611604.3 Other Articles ..........................................................611604.4 Uses Permitted.........................................................611604.5 Uses Not Permitted..................................................611604.6 Construction ............................................................612


Article 605—Office Furnishings (Wired Partitions)................................................................615605.1 Scope .......................................................................615605.2 General ...................................................................615605.4 Partition Interconnections........................................615605.6 Fixed-Type Partitions ..............................................615605.7 Freestanding-Type Partitions...................................616


Article 620—Elevators, Escalators, and Moving Walks ....................................................................................619


Part III. Wiring........................................................................619620.23 Branch Circuit for Machine Room/Machinery

Space........................................................................619

620.24 Branch Circuit for Hoistway Pit..............................619

Part IV. Installation of Conductors .......................................620620.37 Wiring in Elevator Hoistways and

Machine Rooms.......................................................620

Part VI. Disconnecting Means and Control .........................620620.51 Disconnecting Means ..............................................620

Part VIII. Machine Rooms, Control Rooms,Machinery Spaces, and Control Spaces .............................620620.85 GFCI-Protected Receptacles ...................................620


Article 625—Electric Vehicle Charging Systems ........623


Part IV. Control and Protection ............................................623625.22 Personnel Protection System...................................623625.25 Loss of Primary Source ...........................................624625.26 Interactive Systems..................................................624


Article 630—Electric Welders .........................................627


Part II. Arc Welders ...............................................................627630.11 Ampacity of Supply Conductors .............................627630.12 Overcurrent Protection ............................................628630.13 Disconnecting Means ..............................................628

Part III. Resistance Welders .................................................628630.31 Ampacity of Supply Conductors .............................628630.32 Overcurrent Protection ............................................629630.33 Disconnecting Means ..............................................629


Article 640—Audio Signal Processing,Amplification, and Reproduction Equipment ...............631

Part I. General .......................................................................631640.1 Scope .......................................................................631640.2 Definitions ...............................................................631640.3 Locations and Other Articles...................................631640.4 Protection of Electrical Equipment .........................632640.5 Access to Electrical Equipment ..............................632640.6 Mechanical Execution of Work ...............................632640.7 Grounding (Earthing) and Bonding ........................633640.9 Wiring Methods.......................................................633


x


640.10 Audio Systems Near Bodies of Water.....................634

Part II. Permanent Audio System Installations ...................634640.21 Use of Flexible Cords and Flexible Cables.............634640.22 Wiring of Equipment Racks ....................................635640.23 Raceway Fill ............................................................635640.25 Loudspeakers in Fire-Resistance Rated

Partitions, Walls, and Ceilings.................................635Article 640 Questions..............................................636

Article 645—Information Technology Equipment.......637645.1 Scope .......................................................................637645.4 Information Technology Equipment Room.............637645.5 Supply Circuits and Interconnecting Cables ...........638645.6 Cables Not in Information Technology

Equipment Room.....................................................639645.7 Penetrations .............................................................639645.10 Disconnecting Means ..............................................639645.11 Uninterruptible Power Supplies (UPS) ...................639645.15 Grounding (Bonding) ..............................................639


Article 647—Sensitive Electronic Equipment .............641647.1 Scope .......................................................................641647.3 General ....................................................................641647.4 Wiring Methods.......................................................641647.6 Grounding (Bonding) ..............................................642647.7 Receptacles ..............................................................642


Article 680—Swimming Pools, Spas, Hot Tubs,Fountains, and Similar Installations...............................645

Part I. General Requirements for Permanently Installed Pools, Storable Pools, Outdoor Spas,Outdoor Hot Tubs, or Fountains...........................................645680.1 Scope .......................................................................645680.2 Definitions ...............................................................645680.3 Other Articles ..........................................................646680.7 Cord-and-Plug Connected Equipment ....................646680.8 Overhead Conductor Clearance...............................646680.9 Electric Water Heater ..............................................647680.10 Underground Wiring Location ................................647680.11 Equipment Rooms and Pits .....................................647680.12 Maintenance Disconnecting Means ........................647

Part II. Permanently Installed Pools, Outdoor Spas,and Outdoor Hot Tubs...........................................................648680.21 Motors......................................................................648680.22 Area Lighting, Receptacles, and Equipment...........649680.23 Underwater Luminaires ...........................................651

680.24 Junction Boxes.........................................................652680.25 Feeders.....................................................................653680.26 Equipotential Bonding.............................................654680.27 Specialized Equipment ............................................655

Part III. Storable Swimming Pool.........................................655680.30 General ....................................................................655680.32 GFCI-Protected Receptacles ...................................655680.34 Receptacle Locations...............................................656

Part IV. Spas and Hot Tubs ..................................................656680.40 General ....................................................................656680.41 Emergency Switch for Spas and Hot Tubs..............656680.42 Outdoor Installations ...............................................656680.43 Indoor Installations..................................................657680.44 GFCI Protection ......................................................658

Part V. Fountains...................................................................658680.50 General ....................................................................658680.51 Luminaires, Submersible Pumps, and Other

Submersible Equipment ..........................................658680.53 Bonding ...................................................................659680.55 Methods of Grounding (Bonding)...........................659680.56 Cord-and-Plug Connected Equipment ....................659680.57 Signs in or Adjacent to Fountains ...........................659680.58 GFCI-Protected Receptacles ...................................659

Part VII. Hydromassage Bathtubs ........................................659680.70 Protection.................................................................659680.71 Other Electric Equipment........................................660680.72 Other Electrical Equipment .....................................660680.73 Accessibility ............................................................660680.74 Bonding ...................................................................660


Article 690—Solar Photovoltaic Systems ....................663


Article 692—Fuel Cell Systems......................................665692.1 Scope .......................................................................665692.2 Definitions ...............................................................665692.6 Listing Requirement ................................................665


Article 695—Fire Pumps ..................................................667695.1 Scope .......................................................................667695.3 Power Sources .........................................................667695.4 Continuity of Power ................................................667695.5 Transformers............................................................668695.6 Power Wiring...........................................................668

xi


695.7 Voltage Drop............................................................669695.14 Control Wiring.........................................................670


Chapter 7—Special Conditions ..................................673

Article 700—Emergency Power Systems ....................675

Part I. General .......................................................................675700.1 Scope .......................................................................675700.2 Application of Other Articles ..................................676700.3 Equipment Approval................................................676700.4 Tests and Maintenance ............................................676700.5 Capacity...................................................................676700.6 Transfer Equipment .................................................676700.8 Signs ........................................................................677

Part II. Circuit Wiring ............................................................677700.9 Wiring ......................................................................677

Part III. Sources of Power ....................................................677700.12 General Requirements .............................................677

Part IV. Emergency System Circuits for Lighting and Power .............................................................................679700.15 Loads on Emergency Branch Circuits.....................679700.16 Emergency Illumination ..........................................680

Part VI. Overcurrent Protection ............................................680700.25 Accessibility ............................................................680700.26 Ground-Fault Protection of Equipment...................680700.27 Coordination ............................................................680


Article 701—Legally Required Standby Power Systems ...................................................................683

Part I. General .......................................................................683701.1 Scope .......................................................................683701.2 Definitions ...............................................................683701.3 Application of Other Articles ..................................683701.4 Equipment Approval................................................683701.5 Tests and Maintenance ............................................683701.6 Capacity and Rating ................................................684701.7 Transfer Equipment .................................................684701.9 Signs ........................................................................684


Part III. Sources of Power ....................................................684701.11 Legally Required Standby Systems.........................684

Part IV. Overcurrent Protection ............................................686

701.15 Accessibility ............................................................686701.17 Ground-Fault Protection of Equipment...................686701.18 Coordination ............................................................686


Article 702—Optional Standby Power Systems .........689

Part I. General .......................................................................689702.1 Scope .......................................................................689702.2 Definition.................................................................689702.3 Application of Other Articles ..................................690702.4 Equipment Approval................................................690702.5 Capacity and Rating ................................................690702.6 Transfer Equipment .................................................690702.8 Signs ........................................................................690


Part III. Grounding and Bonding...........................................690702.10 Portable Generator Grounding and Bonding ..........690

Part IV. Sources of Power ....................................................690702.11 Outdoor Generator Sets ...........................................690


Article 720—Circuits and Equipment Operating at Less than 50 Volts .........................................................693

Article 720 Question ...............................................694

Article 725—Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits...........695

Part I. General .......................................................................695725.1 Scope .......................................................................695725.2 Definitions ...............................................................696725.3 Other Articles ..........................................................697725.7 Access to Electrical Equipment Behind Panels

Designed to Allow Access.......................................701725.8 Mechanical Execution of Work ...............................701725.11 Safety-Control Equipment.......................................702725.15 Circuit Requirements...............................................702

Part II. Class 1 Circuit Requirements ..................................702725.21 Class 1 Circuit Classifications and Power

Source Requirements...............................................702725.23 Class 1 Circuit Overcurrent Protection ...................703725.25 Class 1 Circuit Wiring Methods..............................703725.26 Conductors of Different Circuits in Same

Cable, Enclosure, or Raceway.................................703725.27 Class 1 Circuit Conductors......................................704725.28 Number of Conductors in a Raceway .....................704

xii


Part III. Class 2 and Class 3 Circuit Requirements ............704725.41 Power Sources for Class 2 and

Class 3 Circuits........................................................704725.42 Equipment Marking.................................................704725.51 Wiring Methods on Supply Side of the

Class 2 or Class 3 Power Source.............................704725.52 Wiring Methods on Load Side of the

Class 2 or Class 3 Power Source.............................705725.55 Separation from Other Systems ..............................705725.56 Conductors of Different Circuits in

Same Cable, Enclosure, or Raceway.......................707725.57 Class 2 or Class 3 Cables Exposed to Lightning ....708725.58 Support ....................................................................708725.61 Applications of Class 2 and Class 3 Cables............709

Part VI. Listing Requirements ..............................................710725.82 Listing and Marking of Class 2 and

Class 3 Cables .........................................................710Article 725 Questions..............................................712

Article 760—Fire Alarm Systems...................................713

Part I. General .......................................................................713760.1 Scope .......................................................................713760.2 Definitions ...............................................................713760.3 Other Articles ..........................................................714760.7 Access to Electrical Equipment Behind Panels

Designed to Allow Access.......................................716760.8 Mechanical Execution of Work ...............................716760.9 Fire Alarm Circuit and Equipment Grounding

(Bonding).................................................................717760.10 Fire Alarm Circuit Identification.............................717760.11 Fire Alarm Circuit Cables Exposed to

Lightning .................................................................717760.15 Fire Alarm Circuit Requirements ............................717

Part II. Nonpower-Limited Fire Alarm (NPLFA) Circuits .....717760.21 GFCI and AFCI Protection......................................717760.23 NPLFA Circuit Overcurrent Protection...................717760.25 NPLFA Circuit Wiring Methods .............................717760.26 Conductors of Different Circuits in

Same Cable, Enclosure, or Raceway.......................718760.27 NPLFA Circuit Conductors .....................................718760.28 Number of Conductors in a Raceway .....................718

Part III. Power-Limited Fire Alarm (PLFA) Circuits .............718760.41 Power Sources for PLFA Circuits ...........................718760.42 Equipment Marking.................................................719760.52 Wiring Methods and Materials on Load Side

of the PLFA Power Source......................................719760.55 Separation from Other Circuit Conductors .............719760.56 PLFA Circuits, Class 2, Class 3, and

Communications Circuits ........................................720

760.58 Support ....................................................................720760.61 Applications of Listed PLFA Cables.......................720

Part IV. Listing Requirements ..............................................721760.81 Listing and Marking of NPLFA Cables ..................721760.82 Listing and Marking of PLFA Cables .....................721


Article 770—Optical Fiber Cables and Raceways......725

Part I. General .......................................................................725770.1 Scope .......................................................................725770.2 Definitions ...............................................................725770.3 Locations and Other Articles...................................726770.6 Optical Fiber Cables................................................727770.9 Types........................................................................727770.12 Raceways for Optical Fiber Cables.........................728770.21 Access to Electrical Equipment Behind

Panels Designed to Allow Access ...........................728770.24 Mechanical Execution of Work ...............................729

Part III. Cables Within Buildings ..........................................729770.113 Listing of Optical Fiber Cables ...............................729770.133 Installation of Optical Fibers and Electrical

Conductors...............................................................729770.154 Applications of Listed Optical Fiber Cables

and Raceways ..........................................................730

Part IV. Listing Requirements ..............................................731770.179 Listing Requirements for Optical Fiber Cables ......731770.182 Listing Requirements for Optical Fiber

Raceways .................................................................732Article 770 Questions..............................................733

Chapter 8—Communications Systems ....................735

Article 800—Communications Circuits.........................737

Part I. General .......................................................................737800.1 Scope .......................................................................737800.2 Definitions ...............................................................737800.3 Other Articles ..........................................................738800.18 Installation of Equipment ........................................739800.21 Access to Electrical Equipment Behind

Panels Designed to Allow Access ...........................739800.24 Mechanical Execution of Work ...............................740800.44 Overhead Communications Wires and Cables ........740

Part II. Conductors Outside and Entering Buildings...........741800.47 Underground Circuits Entering Buildings...............741800.53 Lightning Conductors..............................................741

Part III. Protection .................................................................741


xiii

800.90 Primary Protection...................................................741800.93 Cable Grounding .....................................................741

Part IV. Grounding Methods .................................................741800.100 Cable and Primary Protector Grounding.................741

Part V. Communications Wires and Cables Within Buildings ................................................................................744800.110 Raceways for Communications Circuits .................744800.113 Listing of Communications Wires and Cables........744800.133 Installation of Communications Circuits and

Equipment................................................................744800.154 Applications of Listed Communications Wires,

Cables, and Raceways .............................................746

Part VI. Listing Requirements ..............................................747800.179 Communications Wires and Cables.........................747800.182 Communications Raceways.....................................748


Article 810—Radio and Television Equipment ............751

Part I. General .......................................................................751810.1 Scope .......................................................................751810.3 Other Articles ..........................................................752810.4 Community Television Antenna ..............................752

Part II. Receiving Equipment—Antenna Systems..............752810.12 Support of Lead-In Cables ......................................752810.13 Avoid Contact with Conductors of Other Systems....752810.15 Grounding................................................................753810.18 Clearances................................................................753810.20 Antenna Discharge Unit ..........................................754810.21 Grounding Conductors ............................................754


Article 820—Community Antenna Television (CATV) and Radio Distribution Systems.........................759

Part I. General .......................................................................759820.1 Scope .......................................................................759820.2 Definitions ...............................................................759820.3 Locations and Other Articles...................................760820.15 Energy Limitations ..................................................761820.21 Access to Electrical Equipment Behind Panels

Designed to Allow Access.......................................761820.24 Mechanical Execution of Work ...............................761

Part II. Cables Outside and Entering Buildings...................762820.44 Overhead Cables......................................................762820.47 Underground Circuits Entering Buildings...............762

Part III. Protection .................................................................763820.93 Grounding Cable .....................................................763

Part IV. Grounding Methods .................................................763820.100 Cable Grounding .....................................................763

Part V. Cables Within Buildings ...........................................765820.110 Raceways for Coaxial Cables..................................765820.113 Listing and Markings ..............................................766820.133 Installation of Cables and Equipment .....................766820.154 Applications of Listed CATV Cables and

Raceways .................................................................768

Part VI. Listing Requirements ..............................................769820.179 Additional Listing Requirements ............................769820.182 CATV Raceways .....................................................769


Article 830—Network-Powered Broadband Communications Systems................................................771



Chapter 9—Tables ...........................................................775

Table 1—Conductor Fill ........................................................775Table 4—Raceway Dimensions.............................................776Table 5—Conductor Cross-Sectional Area............................777Table 8—Conductor Properties .............................................778Table 9—AC Impedance for Conductors in Conduit

Tubing ....................................................................778

Annex C—Raceway Fill Tables....................................779

Table C.1—Maximum Number of THNN/THWNConductors in EMT............................................780

Table C.10—Maximum Number of THNN/THWNConductors in RNC..........................................781

UNIT 1—ELECTRICIAN’S MATH AND BASICELECTRICAL FORMULAS..............................................1

Introduction .................................................................1

PART A—ELECTRICIAN’S MATH ..............................................1Introduction .................................................................1

1.1 Whole Numbers...........................................................11.2 Decimal........................................................................11.3 Fractions ......................................................................11.4 Percentages ..................................................................21.5 Multiplier .....................................................................21.6 Percent Increase...........................................................21.7 Reciprocals ..................................................................31.8 Squaring a Number......................................................31.9 Square Root .................................................................41.10 Volume.........................................................................51.11 Kilo ..............................................................................51.12 Rounding Off...............................................................51.13 Parentheses ..................................................................61.14 Testing Your Answer for Reasonableness ...................6

PART B—BASIC ELECTRICAL FORMULAS ...............................7Introduction .................................................................7

1.15 Electrical Circuit..........................................................71.16 Power Source...............................................................71.17 Conductance ................................................................81.18 Circuit Resistance........................................................81.19 Ohm’s Law ..................................................................91.20 Ohm’s Law and Alternating Current ...........................91.21 Ohm’s Law Formula Circle.........................................91.22 PIE Formula Circle....................................................111.23 Formula Wheel .........................................................121.24 Using the Formula Wheel..........................................121.25 Power Losses of Conductors .....................................131.26 Cost of Power ............................................................141.27 Power Changes with the Square of the Voltage ........14

PART C—BASIC ELECTRIC METERS ......................................16Introduction ...............................................................16

1.28 Voltmeter ...................................................................16

1.29 DC Voltmeter .............................................................161.30 DC Ammeter..............................................................171.31 Clamp-on AC Ammeter.............................................171.32 Ohmmeters ................................................................181.33 Wheatstone Bridge ....................................................181.34 Megohmmeter............................................................18

Conclusion.................................................................19

UNIT 2—ELECTRICAL CIRCUITS ...........................49Introduction ...............................................................49

PART A—SERIES CIRCUITS ....................................................49Introduction ...............................................................49

2.1 Practical Uses of the Series Circuit...........................492.2 Understanding Series Calculations............................512.3 Series Circuit Calculations ........................................532.4 Power Calculations....................................................532.5 Variations...................................................................532.6 Series Circuit Notes...................................................532.7 Series-Connected Power Supplies.............................54

PART B—PARALLEL CIRCUITS ...............................................54Introduction ...............................................................54

2.8 Practical Uses of the Parallel Circuit ........................552.9 Understanding Parallel Calculations .........................562.10 Circuit Resistance......................................................572.11 Parallel Circuit Notes ................................................592.12 Parallel-Connected Power Supplies ..........................59

PART C—SERIES-PARALLEL CIRCUITS .................................59Introduction ...............................................................59

2.13 Review of Series and Parallel Circuits ......................602.14 Working Series-Parallel Circuits ...............................602.15 Voltage .......................................................................61

PART D—MULTIWIRE BRANCH CIRCUITS .............................62Introduction ...............................................................62

2.16 Neutral Conductor .....................................................622.17 Grounded Conductor .................................................62

vi

2.18 Current Flow on the Grounded Neutral Conductor .....................................................63

2.19 Balanced Systems......................................................642.20 Unbalanced Current...................................................642.21 Multiwire Branch Circuit ..........................................652.22 Dangers of Multiwire Circuits ..................................662.23 NEC Requirements....................................................67

Conclusion.................................................................68

UNIT 3—UNDERSTANDING ALTERNATING CURRENT ............................................97

Introduction ...............................................................97

PART A—UNDERSTANDING ALTERNATING CURRENT..........97Introduction ...............................................................97

3.1 Current Flow..............................................................973.2 Why Alternating Current is Used..............................983.3 How Alternating Current is Produced .......................983.4 AC Generator.............................................................983.5 Waveform ..................................................................993.6 Sine Wave ..................................................................993.7 Nonsymmetrical Waveform.....................................1003.8 Frequency ................................................................1003.9 Phase........................................................................1013.10 Degrees ....................................................................1013.11 Lead or Lag .............................................................1013.12 Values of Alternating Current..................................101

PART B—CAPACITANCE .......................................................102Introduction .............................................................102

3.13 Charged Capacitor ...................................................1023.14 Electrical Field ........................................................1033.15 Discharging a Capacitor ..........................................1033.16 Determining Capacitance ........................................1033.17 Uses of Capacitors...................................................1043.18 Phase Relationship ..................................................105

PART C—INDUCTION ............................................................105Introduction .............................................................105

3.19 Self-Induction ..........................................................1063.20 Induced Voltage and Applied Current .....................1063.21 Conductor AC Resistance........................................1063.22 Impedance................................................................1073.23 Conductor Shape .....................................................1073.24 Magnetic Cores........................................................1083.25 Self-Induced and Applied Voltage...........................1093.26 Current Flow............................................................1093.27 Phase Relationship ..................................................1093.28 Uses of Induction ....................................................110

PART D—POWER FACTOR....................................................110Introduction .............................................................110

3.29 Apparent Power (Volt-Amperes) .............................1103.30 True Power (Watts)..................................................1113.31 Power Factor............................................................1113.32 Unity Power Factor..................................................1123.33 Power Factor Formulas............................................1123.34 Cost of True Power..................................................1133.35 Effects of Power Factor ...........................................113

PART E—EFFICIENCY ...........................................................114Introduction .............................................................114

3.36 Efficiency Formulas.................................................115

Conclusion...............................................................117

UNIT 4—MOTORS AND TRANSFORMERS......151Introduction .............................................................151

PART A—MOTORS ................................................................151Introduction .............................................................151

4.1 Motor Principles ......................................................1524.2 Dual-Voltage AC Motors .........................................1524.3 Motor Horsepower Rating.......................................1524.4 Motor Current Ratings ............................................1534.5 Calculating Motor FLA...........................................1534.6 Motor-Starting Current............................................1544.7 Motor-Running Current...........................................1554.8 Motor Locked-Rotor Current (LRC).......................1554.9 Motor Overload Protection......................................1554.10 Direct-Current Motor Principles .............................1554.11 Direct-Current Motor Types ....................................1564.12 Reversing the Rotation of a DC Motor ...................1564.13 AC Induction Motor ................................................1564.14 Alternating-Current Motor Types............................1574.15 Reversing the Rotation of an AC Motor .................157

PART B—TRANSFORMERS ..................................................158Introduction .............................................................158

4.16 Transformer Basics .................................................1584.17 Secondary Induced Voltage .....................................1584.18 Autotransformers.....................................................1594.19 Power Losses ...........................................................1594.20 Harmonic Current....................................................1614.21 Efficiency.................................................................1614.22 Transformer Turns Ratio .........................................1614.23 Transformer kVA Rating .........................................1634.24 Current Flow............................................................1634.25 Current Rating .........................................................163

Conclusion...............................................................164

Electrical NEC Exam Preparation Table of Contents

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UNIT 5—RACEWAY AND BOX CALCULATIONS........................................193

Introduction .............................................................193

PART A—RACEWAY FILL ......................................................1935.1 Understanding the NEC, Chapter 9 Tables .............1935.2 Raceway and Nipple Calculations...........................1985.3 Existing Raceway Calculations ...............................1995.4 Tips for Raceway Calculations................................201

PART B—OUTLET BOX FILL CALCULATIONS [314.16] .......2015.5 Sizing Box—Conductors All the Same Size

[Table 314.16(A)] ....................................................2015.6 Conductor Equivalents [314.16(B)] ........................2025.7 Sizing Box—Different Size Conductors

[314.16(B)] ..............................................................204

PART C—PULL BOXES, JUNCTION BOXES,AND CONDUIT BODIES ..........................................................2065.8 Pull and Junction Box Size Calculations ................2075.9 Depth of Box and Conduit Body Sizing

[314.28(A)(2) Ex]....................................................2085.10 Junction and Pull Box Sizing Tips ..........................2085.11 Pull Box Examples ..................................................209

Conclusion...............................................................210

UNIT 6—CONDUCTOR SIZING AND PROTECTION CALCULATIONS.....................237

Introduction .............................................................237

PART A—GENERAL CONDUCTOR REQUIREMENTS.............2376.1 Conductor Insulation Property [Table 310.13] ......2376.2 Allowable Conductor Ampacity [310.15] ...............2396.3 Conductor Sizing [110.6] ........................................2406.4 Terminal Ratings [110.14(C)] .................................2406.5 Conductors in Parallel [310.4] ................................2426.6 Conductor Size—Voltage Drop [210.19(A)(1)

FPN No. 4 and 215.2(A) FPN No. 2] .....................2446.7 Overcurrent Protection [Article 240] ......................2446.8 Overcurrent Protection of Conductors—

General Requirements [240.4] ................................2466.9 Overcurrent Protection of Conductors—

Specific Requirements.............................................2476.10 Equipment Conductor Size and

Protection Examples................................................248

PART B—CONDUCTOR AMPACITY CALCULATIONS ............2496.11 Conductor Ampacity [310.10].................................2496.12 Ambient Temperature Ampacity Correction

Factor [Table 310.16] ..............................................250

6.13 Conductor Bundling Ampacity Adjustment Factor [Table 310.15(B)(2)(a)] ................................251

6.14 Ambient Temperature Correction and ConductorBundling Adjustment Factors .................................253

6.15 Current-Carrying Conductors..................................2546.16 Conductor Sizing Summary ....................................256

Conclusion...............................................................257

UNIT 7—MOTOR CALCULATIONS .......................285Introduction .............................................................285

7.1 Single Motor Conductors [430.22(A)] ....................2857.2 Motor Overcurrent Protection .................................2867.3 Overload Protection [430.6(2) and 430.32(A)].......2877.4 Branch-Circuit Short-Circuit Ground-Fault

Protection [430.51] ..................................................2897.5 Feeder Conductor Size [430.24] .............................2917.6 Feeder Protection [430.61] ......................................2917.7 Highest-Rated Motor [430.17] ................................2927.8 Motor Calculations Steps ........................................2937.9 Motor Calculation Review ......................................2937.10 Motor VA Calculations............................................296

Conclusion...............................................................297

UNIT 8—VOLTAGE-DROP CALCULATIONS......323Introduction .............................................................323

PART A—CONDUCTOR RESISTANCE CALCULATIONS ........3238.1 Conductor Resistance ..............................................3238.2 Conductor Resistance—Direct-Current Circuits

[Chapter 9, Table 8].................................................3258.3 Conductor Impedance—

Alternating-Current Circuits....................................3268.4 Alternating-Current Impedance as Compared to

Direct-Current Resistance .......................................3268.5 Impedance [Chapter 9, Table 9] ..............................326

PART B—VOLTAGE-DROP CALCULATIONS..........................3298.6 Voltage-Drop Considerations ..................................3298.7 NEC Voltage-Drop Recommendations....................3298.8 Determining Circuit Conductors’ Voltage Drop......3308.9 Sizing Conductors to Prevent Excessive

Voltage Drop............................................................3328.10 Limiting Conductor Length to Minimize

Voltage Drop............................................................3338.11 Limiting Current to Limit Voltage Drop .................3348.12 Extending Circuits ...................................................335

Conclusion...............................................................336

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UNIT 9—DWELLING UNIT CALCULATIONS ....365Introduction .............................................................365

PART A—GENERAL REQUIREMENTS ...................................3659.1 General Requirements .............................................3659.2 Voltages [220.5(A)] .................................................3659.3 Fraction of an Ampere [220.5(B)]...........................3659.4 Small-Appliance Circuits [210.11(C)(1)] ...............3669.5 Cooking Equipment—Branch Circuit

[Table 220.55, Note 4].............................................3679.6 Laundry Receptacle(s) Circuit [210.11(C)(2)]........3699.7 Lighting and Receptacles ........................................369

PART B—STANDARD METHOD—FEEDER/SERVICE LOAD CALCULATIONS..............................3719.8 Dwelling Unit Feeder/Service Load Calculations

(Article 220, Part III)...............................................3719.9 Dwelling Unit Feeder/Service Calculations

Examples .................................................................372

PART C—OPTIONAL METHOD—FEEDER/SERVICE LOAD CALCULATIONS..............................3769.10 Dwelling Unit Optional Feeder/Service

Calculations [220.82] ..............................................3769.11 Dwelling Unit Optional Calculation Examples ......3779.12 Neutral Calculations—–General [220.61]...............378

Conclusion...............................................................380

UNIT 10—MULTIFAMILYDWELLING CALCULATIONS .....................................411

Introduction .............................................................41110.1 Multifamily Dwelling Unit Calculations—

General ....................................................................411

PART A—STANDARD METHOD—FEEDER/SERVICE LOAD CALCULATIONS..............................41310.2 Multifamily Dwelling Unit Calculation

Examples—Standard Method..................................41310.3 Multifamily Dwelling Unit Calculations—

Standard Method .....................................................419

PART B—OPTIONAL METHOD—FEEDER/SERVICE LOAD CALCULATIONS..............................42110.4 Multifamily Dwelling Unit

Calculations [220.84]—Optional Method...............42110.5 Multifamily—Optional Method

Example 1 [220.84] .................................................42210.6 Multifamily—Optional Method

Example 2 [220.84] .................................................424

Conclusion...............................................................426

UNIT 11—COMMERCIAL CALCULATIONS ......455Introduction .............................................................455

PART A—GENERAL ...............................................................45511.1 General Requirements .............................................45511.2 Conductor Ampacity [Article 100]..........................45511.3 Conductor Overcurrent Protection [240.4]..............45611.4 Voltages [220.5(A)] .................................................45611.5 Rounding an Ampere [220.5(B)].............................45611.6 Air-Conditioning Branch Circuit.............................45711.7 Dryers ......................................................................45811.8 Electric Heat ............................................................45911.9 Kitchen Equipment..................................................46011.10 Laundry Equipment .................................................46111.11 Lighting—Demand Factors

[Tables 220.12 and 220.42] .....................................46211.12 Lighting Without Demand Factors [215.2(A)(1),

230.42(A)(1), and Table 220.12].............................46211.13 Lighting-Miscellaneous...........................................46311.14 Multioutlet Receptacle Assembly [220.14(H)] .......46311.15 Receptacle VA Load ................................................46411.16 Banks and Offices—General Lighting

and Receptacles [220.14(K)]...................................46511.17 Signs [220.14(F) and 600.5]....................................467

PART B—STANDARD METHOD—FEEDER/SERVICE LOAD CALCULATIONS..............................46711.18 Feeder/Service Load Calculation ............................46711.19 Neutral Calculations [220.61] .................................467

PART C—EXAMPLES ............................................................46911.20 Bank (120/240V, single-phase) ..............................46911.21 Marina [555.12].......................................................47011.22 Mobile/Manufactured Home Park [550.31] ............47111.23 Office Building (277/480V, Three-phase) ...............47211.24 Recreational Vehicle Park [551.73].........................47411.25 Restaurant—Standard Load Calculation

(120/208V, Three-phase) .........................................474

PART D—OPTIONAL METHOD—FEEDER/SERVICE LOAD CALCULATIONS..............................47611.26 New Restaurant—Optional Method [220.88] .........47611.27 School—Optional Method [220.86]........................478

PART E—ELECTRIC WELDERS .............................................47911.28 Arc Welders .............................................................47911.29 Resistance Welders ..................................................48011.30 Light Industrial Calculation ....................................481

Conclusion...............................................................482

Electrical NEC Exam Preparation Table of Contents

ix

UNIT 12—DELTA/DELTA AND DELTA/WYE TRANSFORMERS ...............................511

Introduction .............................................................511Definitions ...............................................................511

12.1 Current Flow............................................................515

PART A—DELTA/DELTA TRANSFORMERS ..........................51612.2 Delta Transformer Voltage.......................................51612.3 Delta High-Leg........................................................51612.4 Delta Line Currents .................................................51712.5 Delta Phase Currents ...............................................51712.6 Delta Phase versus Line Current .............................51812.7 Delta Current Triangle.............................................51912.8 Delta Transformer Balancing ..................................52012.9 Delta Transformer Sizing ........................................52112.10 Delta Panel Balancing .............................................52112.11 Delta Panelboard and Conductor Sizing .................52112.12 Delta Neutral Current ..............................................52212.13 Delta Maximum Unbalanced Load .........................52312.14 Delta/Delta Example ...............................................523

PART B—DELTA/WYE TRANSFORMERS..............................52612.15 Wye Transformer Voltage ........................................52612.16 Wye Voltage Triangle ..............................................52612.17 Wye Transformers Current ......................................52612.18 Wye Line Current ....................................................52712.19 Wye Phase Current ..................................................52712.20 Wye Phase versus Line Current ..............................52812.21 Wye Transformer Balancing....................................52912.22 Wye Transformer Sizing..........................................53012.23 Wye Panel Balancing...............................................53012.24 Wye Panelboard and Conductor Sizing...................53112.25 Wye Neutral Current ...............................................53112.26 Wye Maximum Unbalanced Load...........................53212.27 Delta/Wye Example.................................................53212.28 Delta versus Wye.....................................................536

Conclusion...............................................................536

INDEX..................................................................................567

Table of Contents Electrical NEC Exam Preparation

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vi

Introduction .............................................................................vii

Passing the Exam ..................................................................viii

The National Electrical Code...................................................xi

About the Author ....................................................................xvi

Unit 1Review Quiz—Articles 90 through 200 ....................................1Practice Quiz—Articles 80 through 110 .................................14Challenge Quiz—Articles 90 through Annex C......................21

Unit 2Review Quiz—Articles 200 through 230 ................................28Practice Quiz—Articles 200 through 230 ...............................41Challenge Quiz—Articles 90 through Annex C......................48

Unit 3Review Quiz—Articles 230 through 250 ................................55Practice Quiz—Articles 230 through 250 ...............................68Challenge Quiz—Articles 90 through Annex C......................75

Unit 4Review Quiz—Articles 250 through 310 ................................82Practice Quiz—Articles 250 through 310 ...............................96Challenge Quiz—Articles 90 through Annex C....................103

Unit 5Review Quiz—Articles 310 through 342 ..............................110Practice Quiz—Articles 310 through 342 .............................124Challenge Quiz—Articles 90 through Annex C....................130







Unit 12Review Quiz—Articles 702 through Annex C ......................308Practice Quiz—Articles 702 through Chapter 9....................322Challenge Quiz—Articles 90 through Annex C....................328

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