Arc FlashBoundaries & Design for Safety

NFPA 70E- Requirements for Two Types of Boundaries Shock Flash

Knowing the boundaries not enoughNeed to know PPE, Tools, etc.

In practice, need to address both boundary types in integrated manner.

What are the NFPA 70E requirements for shock hazard and arc flash hazard?

NFPA 70E Boundaries70E-2000 P. 10-11Shock Protection BoundariesLimited Approach Boundaryentered only by qualified persons or unqualified persons escorted by qualified personRestricted Approach Boundaryentered only by qualified persons required to use shock protection techniques and equipmentProhibited Approach Boundaryentered only by qualified persons requiring same protection as if direct contact with live part Flash Protection Boundarylinear distance to prevent serious injury from a potential arc-flash

Shock Hazard Approach Boundaries(from NFPA 70E-2000)

70E-2000 P. 51

Column Number (1)

(2)

(3)

(4)

(5)

Nominal System Voltage Range

Limited approach Boundary

Restricted Approach Boundary

Prohibited Approach Boundary

Phase-to-Phase

ExposedMovableConductor

Exposed FixedCircuit Part

Includes Inadvertent Movement Adder

Includes Reduced Inadvertent Movement Adder

Energized Part to Employee - Distance in feet - Inches

50 V and less

Not Specified

Not Specified

Not Specified

Not Specified

Over 50 V, not over 300 V

10 ft. 0 in.

3 ft. 6 in.

Avoid Contact

Avoid Contact

Over 300 V, not over 750 V

10 ft. 0 in.

3 ft. 6 in.

1 ft. 0 in.

0 ft. 1 in.

Over 750 V, not over 15 kV

10 ft. 0 in.

5 ft. 0 in.

2 ft. 2 in.

0 ft. 7 in.

Over 15 kV, not over 36 kV

10 ft. 0 in.

6 ft. 0 in.

2 ft. 7 in.

0 ft. 10 in.

Limited Shock Boundary:Qualified or Unqualified Persons* * Only if accompanied by Qualified PersonProhibited Shock Boundary:Qualified Persons Only. PPE as if direct contact with live part Restricted Shock Boundary:Qualified Persons OnlyNote: shock boundaries dependent on system voltage level Flash Protection Boundary (FPB)Must wear appropriate PPEFPB dependent on fault level and time duration.Equipment

Flash Protection Boundary CalculationsTest 4Test 3Test 126.7 in. 640 A Non Current-Limiting OCPD 6 cycles open3.74 in. 601 A Current-Limiting OCPD 1.61 in. 30 A Current-Limiting OCPDExamples for tests on videos

It is not intended to degrade any equipment manufacturer, but rather to show the possible results of accidental short circuits,

Safety BASICsTMCurrent-Limitation - Arc-Energy ReductionNon-Current LimitingReduced Fault Currentvia Current-LimitationTest 1Test 4Test 3

Flash Hazard - NFPA 70EPart II - Chapter 2Part II 2-1.3.3 Flash Hazard Analysis.Flash hazard analysis shall be done before a person approaches any exposed electrical conductor or circuit part that has not been placed in an electrically safe work conditions.What is required?1. Determine Flash Protection Boundary2. Determine the Personnel Protective Equipment

70E-2000 P. 50

Flash Hazard How?1. Determine Flash Protection Boundary:Calculate using Isca & clearing time (or use tables - many qualifiers) (or default to four feet - 600 V or less)2. Determine the Personnel Protective Equipment :A. Calculate incident energy exposure level for distance of workers face and chest from the possible arc source (18 typical - considers the head and torso but not the hands and arms). B. Select appropriate PPE for incident energy.

Flash Hazard AnalysisFlash Protection Boundary Calculations1) (600 V or less) Distance formula based on fault available and clearing time of overcurrent protective device:DC = [2.65 x MVAbf x t] 1/2 ) ft

where MVAbf = 1.73 (Isca) (Voltage) x 10-6 2) (> 600 V) Distance based on where incident energy level is 1.2 or 1.5 cal/cm2

Flash Hazard Analysis -Example 1Flash Protection Boundary CalculationCircuit using non-current limiting circuit breakerSafety Basics

Flash Hazard Analysis - Example 2Flash Protection Boundary CalculationCircuit using current limiting fusesSafety Basics

Flash Protection Boundaries need to be calculated for all levels of fault current.Flash Hazard Analysis

To select proper Personal Protective Equipment (PPE), calculate incident energy. This is a measure of the thermal energy at a specific distance from the arc flash.

Units: calories per cm2Incident Energy

Second Degree Burn Threshold1.2 cal/cm2Note: medical treatment may still be required if bare skin is exposed to this level of flash - full recovery to be expected.

Flash Hazard Analysis Formula:EMB = 1038.7 DB-1.4738 tA[0.0093F2-.3453F+5.9675] cal/cm2

EMB = Incident Energy (cal/cm2)DB = Distance, (in.) [for Distances > 18 inches] tA = Arc Duration, (sec.)F = Bolted Fault Short Circuit Current [16KA to 50kA]70E-2000 P. 71 B-5.2 Incident Energy Calculation

Flash Hazard Analysis - Example 1Incident Energy Calculation @ 18Circuit using non-current limiting circuit breaker

Flash Hazard Analysis Incident Energy Calculation @ 18Example 1: 40896 amps of available fault current, 480 volt 3 phase system, Non-current limiting overcurrent device 6 cycle (0.1 sec) opening time. EMB = 1038.7 DB-1.4738 tA[0.0093F2-.3453F+5.9675] EMB = 1038.7 (18)-1.4738(.1) [0.0093(41)2- .3453(41)+5.9675] EMB = 10.92 cal/cm2

Flash Hazard Analysis - Example 2Incident Energy Calculation @ 18Circuit using current limiting fuses

Incident energy exposure needs to be calculated for all levels of fault current.Flash Hazard Analysis

Comparison of Example 1 & 2Flash Protection BoundaryIncident Energy @ 18 inchesExample 1non current- limiting6 cycle openingExample 2current-limiting1/4 cycle clearing36 inches 10.92 cal/cm2 Less than .17 cal/cm22.76 inches

Flash Hazard - NFPA 70EPart II - Chapter 2NFPA 70 E permits some alternative ways to calculate Flash Protection Boundary and Personal Protective Equipment necessary for hazard analysis. The alternatives are different for 600 Volts or less and greater than 600 volts.When using the alternatives it is necessary to be attentive to the specified qualifiers and footnotes. Full calculations provide for the most accurate assessment and in some cases, full calculations are required.70E-2000 P. 50

Flash Hazard - NFPA 70EPart II - Chapter 2Flash Protection Boundary 600 Volts or less1. Default to four feet (based on 300kA-cycles) (50,000 amps fault - six cycles to clear)2. Alternatively - may calculate if less than 300kA-cycles- must calculate if over 300kA-cycles3. Alternatively - can follow Personal Protective Equipment (PPE) requirements of 3-3.9 of Part II (P 55 & 59) (this alternative does not take advantage of current-limitation & has footnotes for condition qualifiers) 70E-2000 P. 50

Page 55 Table 3-3.9.1 (1) Read Headings (2) 600 V Class MCC (3) Read Notes 2 & 3 (P. 58) (4) Work on energized parts (5) What is required? (6) 2* (P. 58), V gloves, V toolsPage 59 Table 3-3.9.2 (1) What is required (2) Read legend & notes (P. 60)NFPA 70E: Simply Use Tables Per Task

Page 55, Table 3-3.9.1/ Page 59,Table 3-3.9.2600 V Class MCC - Work on energized parts including voltage testing - What is required? V-rated gloves V-rated tools Doubled-layered switching hood and hearing protection Untreated natural fiber: T-shirt & Long pants FR Clothing: Long sleeve shirt, Pants, Coveralls FR Protective Equipment: Hard hat, safety glasses, leather gloves, leather work shoes(Note there are footnotes altering above due to fault current levels and duration. And there are some substitutions permitted.)

NFPA 70E: Simply Use Tables Per Task

Flash Hazard - NFPA 70EPart II - Chapter 2Flash Protection Boundary above 600 Volts 1. Calculated distance where incident energy is:A. 1.5 cal/cm2 where fault clearing time is 0.01 seconds or less B. 1.2 cal/cm2 fault clearing greater than 0.01 seconds2. Alternatively - can follow Personal Protective Equipment (PPE) requirements of 3-3.9 of Part II (this alternative does not take advantage of current-limitation & has footnotes for condition qualifiers)

70E-2000 P. 50

Flash Hazard Analysis- OCPD Opening TimesSafety Basics

Flash Hazard - NFPA 70EPart II - Chapter 2To enter or work within Flash Protection Boundary: shall do flash hazard analysisemployer shall document incident energy exposure of workerworker shall use appropriate flame resistant (FR) clothing and personal protective equipment (PPE) for level of incident energy exposure

Design for Safety Electrical System Work Practices

Design for SafetyElectrical System DesignGeneral DesignNon - Current Limiting OCPD DesignCurrent Limiting OCPD Design

General DesignSpecify Insulated BusReduces ChanceSelf Extinguish (600V and below)

General Design Use Remote Switch Operator on Medium Voltage Switches and Circuit Breakers

Isolate the CircuitDisconnects capable of Lockout/TagoutIn Sight Motor Disconnects Selectively Coordinated overcurrent protection General Design

General Design Motor Disconnects Within Sight

NFPA 70E requires covers or barriers be installed if a worker could accidentally contact energized parts 50 volts and above:

Finger-Safe guards and covers reduce the chance of incident occurrence

IEC60529Safety BasicsGeneral DesignIP20 IP 2 0International ProtectionProtection against solid objects2 - 12mm (finger)Protection against liquids0 - no protection

Specify & Install Finger Safe (IP20) Electrical Products

General DesignTypical 1200A MCCSplit Large Feeder

General DesignReduces Wire SizeReduces OCPD SizeReduces Short Circuit Current

Non-Current Limiting OCPD DesignDesign using High Impedance Components

Helps to Limit potential arc energy

Non-Current Limiting OCPD DesignNo Short Time Delays on Circuit BreakersPanelboards, Switchboards, and MCCs tested for only 3 cycles.Increases time fault existsSelective Coordination can be achieved with other devices.

Current Limiting OCPD Design

Use Current Limiting Overcurrent Protective Devices: Current-limiting Circuit Breakers Current-limiting Fuses

Current Limiting OCPD Design

Use Overcurrent Protective Devices with the Highest Degree of Current-LimitationFuses: Use Class J, CC, T, RK1, LRather than Class RK5Definitely not Class H Current Limiting CBs: Determine degree of current-limitation

Current Limiting OCPD DesignSize OCPD Devices as Small as PossibleHigher Degree of C.L.Class L1200A50 KA Available23 KA Let ThroughClass RK1600A50 KA Available15 KA Let Through

Current Limiting OCPD DesignSize OCPD Devices as Small as PossibleSize Motor OCPD lower than Code MaxCode Max = 125A

Optimal Sizing = 100A* See Motor Tables in the SPD50 HP 480VFLA = 65A

Current Limiting OCPD DesignSpecify Type 2 No Damage Protection for Motor Starters Backed by Testing Limits Energy Let Through

Current Limiting OCPD DesignDesign using Low Impedance ComponentsMaximizes Current LimitationBetter Voltage RegulationPower Loss Minimized

Design for SafetyWork Design

Safety Basics

Safety PrinciplesTraining, Planning and Writing ProceduresPlan every jobAnticipate Unexpected ResultsUse Procedures as ToolsIdentify the HazardAssess Peoples Abilities

Safety PrinciplesProviding an Electrically Safe Work ConditionUse the Right Tool for the JobIsolate the EquipmentProtect the PersonMinimize the HazardAudit these Principles

Hazard/Risk AnalysisHazard/Risk Analysis is a decision making process required to:evaluate circuit information drawingsdetermine the degree and extent of hazardsjob planning necessary to safely perform taskdetermine Shock Approach Boundaries requirements determine Flash Protection Boundary requirementsdetermine Incident Energy Exposure determine appropriate Personal Protective Equipment (PPE) based on the potential hazards presentevaluate personnel qualificationsSafety Basics

110.16 2002 NEC New Arc Flash Hazard Marking Requirement

110.16 Flash Protection. Switchboards, panelboards, industrial control panels, and motor control centers in other than dwelling occupancies, that are likely to require examination, adjustment, servicing, or maintenance while energized, shall be field marked to warn qualified persons of potential electric arc flash hazards. The marking shall be located so as to be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment.

FPN No. 1: NFPA 70E-2000, Electrical Safety Requirements for Employee Workplaces, provides assistance in determining severity of potential exposure, planning safe work practices, and selecting personal protective equipment.

FPN No. 2: ANSI Z535.4-1998, Product Safety Signs and Labels, provides guidelines for the design of safety signs and labels for application to products.

Reprinted from NEC 2002

WARNING !Arc Flash and Shock HazardAppropriate PPE RequiredCourtesy E.I. du Pont de Nemours & Co.

Equipment Name: Slurry Pump StarterWARNING !Arc Flash and Shock HazardAppropriate PPE RequiredCourtesy E.I. du Pont de Nemours & Co.

Equipment Name: Slurry Pump StarterWARNING !Arc Flash and Shock HazardAppropriate PPE RequiredCourtesy E.I. du Pont de Nemours & Co.

What Are the OSHA Regulations and NFPA 70E Requirements for Workingon Live Equipment? 2001 Cooper Bussmann, Inc.

Safe Work Practices not to work hot or live except :1. Deenergizing introduces additional or increased hazards2. Infeasible due to equipment design or operational limitationsOSHA 1910.333 (a) (1) & NFPA 70E 2-1.1.1Wearing Proper PPE?

Safe Work Practices

(It is recommended that this presentation be made after Electrical Hazards PowerPoint and Bussmann Safety Basics Film. It is also recommended that the Bussmann Safety Basics Handbook be studied and referenced. Also, it is suggested to study and reference specific NFPA 70 E requirements.)

This presentation will examine the requirements for arc flash boundaries and provide some suggestions for designing electrical systems with worker safety in mind . There are two specific type hazard boundaries required in NFPA 70E; shock and flash. However, in order to work within the boundaries requires the proper personal protective equipment, tools, work procedures etc. In practice it is necessary to assess both the shock boundaries and flash boundaries in an integrated manner. In other words, one should not assess the shock boundaries and then proceed to work. The flash protection boundary may be at a greater distance than one of the critical shock boundaries. NAPA 70 E has specific requirements for both shock and arc flash boundaries. There are three specific shock boundaries in NFPA 70E. (It is suggested you read the definitions for each from NFPA 70E or use Safety Basics Handbook.) The flash protection boundary is the distance at which a just curable burn could occur to bare skin. A burn at this level may still require medical attention.This table is from NFPA 70 E and is reprinted in Safety Basics handbook

Approach Boundaries establishes satisfactory distances between persons (qualified and unqualified) and potentially energized conductors. Limited Approach Boundary (columns 2 and 3) - Qualified persons are allowed to cross the boundary. Unqualified persons are not permitted to cross this boundary unless they are escorted by a qualified person.Restricted Approach Boundary (column 4) - Under no circumstances shall an unqualified person be permitted to cross this boundary. To cross this boundary, the person must:be a qualified person, have an approved plan with a hazard/risk analysis, use personal protective equipment approved for the conditions, and must be able to position his or her body in a way that minimizes risk of inadvertent contact.Prohibited Approach Boundary (column 5) - This is the minimum approach distance to an exposed and potentially energized conductor and is the closest point to prevent flashover. To cross this boundary and enter the prohibited space shall be considered the same as making contact with exposed energized conductors.This depicts what the boundaries might look like for a typical system.

NFPA 70E stipulates three shock boundaries and a flash protection boundary that must be known and observed.The shock boundaries, dependent on the system voltage, can be found in a NFPA 70E table. The arc flash hazard must also be assessed prior to working on equipment.

NFPA 70E also provides means to determine the flash protection boundary. It is possible to calculate the Flash Protection Boundary (FPB) and Incident Energy Exposure level, when the available bolted short circuit current, the minimum sustainable arcing fault current, and the time duration for the equipment supply overcurrent protective device to open are known. NFPA 70E provides the formulas for this critical information as well as other important information on safe work practices, personal protection equipment and tools to use.

A qualified worker should not enter the flash protection boundary to work on or near live parts unless he/she is wearing the PPE for the level of hazard that could occur.

- Lets relate the distances to what we saw in the tests in Electrical Hazards PowerPoint.-Test 4The ball of fire encompasses the primary worker for much of the test. Notice how this matches closely with formula. The flash protection boundary calculated to 26.7 inches.-Test 3The initial ball of fire extends out to the primary workers chest. However due to the reduced exposure time, the damaging heat is isolated within a foot at 3.74 inches. Note the majority of the flash is inside the panel by the workers hand.-Test 1The slight flash that was seen only migrated out to the workers hand. With the limited time of exposure, the damaging heat is isolated within a couple inches (1.61 inches). The shank on a screwdriver is generally longer than this distance. This illustrates the likeness of the currents that flowed for the three tests from Test 4, 3, and 1 shown in Electrical Hazards Presentation and shown in the prior slide. In Test 4, the overcurrent protective device took 6 cycles ( .1 second) to clear the fault. In Test 3 the overcurrent protective device took a quarter of a cycle (.004 seconds) to open and it limited (cut off) the magnitude of current thus greatly reducing the energy let-thru. In Test 1, the overcurrent protective device opened in less than a quarter of a cycle and greatly limited the current thus greatly reducing the arc flash energy.Self explanatory. Read NFPA section sited.

To comply one can determine the Flash Protection Boundary and then determine the PPE required. How do you do this. There is an equation in NFPA 70E to calculate the flash protection boundary. For three phase systems the three phase bolted fault current and clearing time of the overcurrent protective devices are values that are needed to do the calculations. There are other alternatives to determine the flash protection boundaries. There is a four foot default for 600 volt and less systems and then the selection of the tools and PPE can be read from two sets of tables. The incident energy can be calculated using an equation in NFPA 70E. Then the appropriate PPE can be selected.

Flash boundary is the linear distance from a potential flash hazard. This distance is used to determine where flash protective Personal Protective Equipment should be used.These calculations were first developed and then presented by Ralph H. Lee in a technical paper - The Other Electrical Hazard: Electrical Arc Blast Burns, IEEE Transactions on Industrial Applications, Volume IA-18, No. 3, May/June 1982. And after careful study and testing they were adopted by the NFPA 70E in 1995.A Flash Protection Boundary Calculation should be made:for all panelboards, loadcenters, switchboards, switchgear, mccs, disconnects, etc. for all but individual residential applicationsand especially when a circuit breaker is using a Short Time Delay (STD) feature

Personal Protective Equipment needs to be selected that protects the person from the maximum thermal exposure that could be encountered. Incident energy is a measure of thermal energy and can be calculated by an equation in NFPA 70 E appendix. PPE is rated for thermal protection.

Flash boundary is the linear distance from a potential flash hazard. This distance is used to determine where flash protective Personal Protective Equipment should be used.

Dc=Flash Protection Boundary (Distance of person from an arc source for a just curable burn [in ft.]) MVAbf =Bolted 3-phase fault MVA at point involved=1.73 x voltage L-L x Available short-circuit current x 10-6MVA=MVA rating of transformer (For transformers with MVAratings below 0.75 MVA, multiply the transformer MVArating by 1.25.)t=Time of arc exposure in seconds

(See Safety Basics Book)Example 1 - Circuit with a non-current limiting over-current protective device.

Note the following information is needed to conduct the Flash Protection Boundary Calculation:Available Fault CurrentOpening time of the circuit protection device - use the Short Time Delay setting if STD feature is used and the nominal voltage

In this example shown the calculation for the flash protection boundary is three feet.See Safety Basics Book Page 27.Example 2 - Circuit with a current limiting over-current protective device.

Note again that the following information is needed to conduct the Flash Protection Boundary Calculation:Available Fault CurrentOpening time of the fuse (or current limiting circuit breaker) while in its current-limiting range. Use 0.004 seconds (or 1/4 cycles) unless actual opening time is known.And the nominal voltage

In this example shown the calculation for the flash protection boundary is .23 feet. The reduction from the previous example is due to the current limitation of the overcurrent protective device.

The previous example was calculated using the maximum available bolted fault current. Additional calculations should be performed for lower levels of fault current, down to the lowest level of sustainable arcing fault current, to assure the maximum Flash Protection Boundary is discovered.Incident energy is measured in calories/cm squared. This is used to measure the level of thermal energy. It is possible to measure the expected incident energy that might occur under arcing fault situation and then select PPE that has sufficient cal/cm squared (thermal) capabilities.- 1.2 cal/cm2 is considered the threshold for second degree burns. Bare skin exposed at this level may still require medical treatment.

(Supplemental Reading IEEE papers, Predicting Incident Energy to Better Manage the Electric Arc Hazard on 600V Power Distribution Systems and Protective Clothing Guidelines for Electric Arc Exposure)

See NFPA 70 E Appendix to Chapter II, page 71.

EMB = maximum 20 in. cubic box incident energy, cal/cm2 DB = distance from arc electrodes, inches (for distances 18 in. or greater) tA= arc duration, seconds F= bolted fault short circuit current, kA (for the range of 16 KA to 50 kA)

This equation was derived and then presented by R.L. Doughty, T.E. Neal, and H.L. Floyd, II in a technical paper - Predicting Incident Energy to Better Manage the Electric Arc Hazard on 600V Power Distribution Systems, IEEE IAS 45th Annual Petroleum and Chemical Industry Conference, September 28-30, 1998.

A Incident Energy Calculation should be made when work is to be performed within the Flash Protection Boundary and used to determine the level of Flame Resistant (FR) Clothing and Personal Protective Equipment (PPE) to be used.Example of calculation of incident energy that could occur under arcing fault conditions. Answer is 10.92 cal/cm sq.

Example 3 - Circuit with a non-current limiting over-current protective device.

Note the following information is needed to conduct the Incident Energy Calculation:Available Fault CurrentOpening time of the circuit protection device - use the Short Time Delay setting if STD feature is used Distance from arcNote: Use 18 in. for distances < 18 inchesThis is the calculation for the prior slide.

Example 1 - Calculation:The example shown here is a non-current limiting deviceThe Incident Energy Calculation determines the level of Protective Clothing. Refer to Table 3-3.9.3 in NFPA70E/2000 edition for weight of FR clothing required.Example of calculating incident energy with current limiting protective device protecting.

Example 2 - Circuit with a current limiting over-current protective device.

Note again that the following information is needed to conduct the Flash Protection Boundary Calculation:Available Fault CurrentOpening time of the fuse (or current limiting circuit breaker) while in its current-limiting range. Use 0.004 seconds (or 1/4 cycles) unless actual opening time is known.Distance from arcNote: Use 18 in. for distances < 18 inches

This is the calculation for the prior slide.

Example 1 - Calculation:The example shown here is using a current limiting protective deviceThe Incident Energy Calculation determines the level of Protective Clothing. Refer to Table 3-3.9.3 in NFPA70E/2000 edition for weight of FR clothing required.

The previous example was calculated using the maximum available bolted fault current. Additional calculations should be performed for lower levels of fault current, down to the lowest level of sustainable arcing fault current, to assure the maximum incident energy is discovered.This table compares the flash protection boundary and incident energy for both example 1 and 2 just covered in previous slides. It illustrates the benefit of current limiting protective devices in reducing the risk. Please note that it is important to assess the flash protection boundary and incident energy for the full range of possible arcing fault magnitude and respective opening times of the overcurrent protective devices.See NFPA 70E for the various alternatives to determine the flash protection boundary. If you study these you will find that the simpler alternatives have some limitations or restrictions. You will need to understand the qualifiers for each method. The most accurate way is to calculate the FBP using the equation. For 600 volt or less systems, here are the alternatives:(read slide)One alternative is to use Tables. To better understand this tool it is best to do a specific example. Do one step at a time. Be sure to read the Notes and Legend of each Table. If you do not have the NFPA 70E-2000 tables mentioned in the previous slide (or this slide) then this is the results for one particular work task. Shown is the PPE and tools determined by using the tables for the 600 volt class motor control center when the task is to work on energized parts. This includes voltage testing the equipment which is one of the steps in placing a circuit in a safe work condition.

Using the tables results in the PPE shown on the slide. However, each table has a legend and notes that can alter the selection of PPE. These notes permit substitutions in some cases. The notes have qualifiers where the table is not permitted to be used. A case in point in some circumstances is when the available fault current is too high or if the duration of the fault clearing is too long. For instance, in the above example, the qualifier is that the fault current has to be less than 65,000 amperes short-circuit current available, 0.03 seconds (2 cycle) fault clearing. If the fault current is not lower than this criteria then these tables can not be used. The incident energy would have to be calculated and the proper PPE selected using the calculated values.The Flash Protection Boundary is determined a bit different for systems greater than 600 volts.As you have learned, the clearing time of the overcurrent protective device is very important to the determination of the flash protection boundary and incident energy. This table provides Industrial accepted opening times for overcurrent protection devices. This table is also found in the Bussmann SPD.If a worker is to approach live parts, it is necessary to do a flash protection analysis. The employer shall document the incident energy that could be possible and the worker must have on the proper PPE.Following are some suggestion for designing electrical systems to reduce electrical hazards. Plus work practices can be designed for safety. - The following design considerations are well documented in IEEE papers.- They can be classified into three main categories:General DesignNon Current Limiting DesignCurrent Limiting DesignSupplemental Reading (Papers on Bussmann Website):

- Arcing Flash/Blast Review with Safety Suggestions for Design and Maintenance-The Use of Low Voltage Current Limiting Fuses to Reduce Arc Flash Energy- Using Current-Limiting Fuses to Reduce Hazards Due to Electrical Arc- Flashes

-Specify Insulated Bus Reduces chance of accidental contact or anything laying across the busesProven greater chance to self extinguish arcing faults-Supplemental Reading:

- Arcing Flash/Blast Review with Safety Suggestions for Design and Maintenance (IEEE paper)

- Use remote operated switch or circuit breaker operators, especially for medium voltage application. This permits workers to be at a good distance for an operation that has a higher rate of serious incidents.

ISOLATE THE CIRCUITRequest Bussmann disconnects (UL 98) with selector or pistol handles which are Padlockable as required by codes and standardsRequest Bussmann disconnects (UL 98 and UL 508) at all motor loads to supplement the main disconnect where needed.Request Bussmann LOW-PEAK fuses sized to offer Selective Coordination.The 1999 NEC required a disconnect in sight of a motor or machine. However, there was an exception that if the disconnect at the controller that was out of sight could be locked out, then the insight disconnect could be omitted.

The 2002 NEC has a tighter requirement. An insight disconnect is required, with some exceptions, for some specific industrial applications. An insight motor disconnect is more likely to be used by a worker for the lockout procedure to put equipment in a safe work condition prior to doing work on the equipment.Use finger safe products. These type products are more and more prevalent in the market place. A finger safe component can reduce the occurrence of electrical incidents. Even if the worker accidentally touches one of these components he will not get a shock. So these type products can reduce the chance that electrocution or arcing faults occur. Finger safe products reduce the chance that a shock or arcing fault can occur. If all the electrical components are finger safe, a worker has a much lower chance of coming in contact with a live part.

Shown are the new CubeFusesTM that are IP20 finger safe. In addition, they are a very current-limiting protective device.Also shown are SAMITM covers for fuses, Safety JTM holders for LPJ fuses, and CH holders available for a variety of Buss fuses. All these devices reduce the chance that a worker or tool will come in contact with a live conductor.

Fuse and terminal shrouds for disconnect switches are also pictured.

All of these products make for a safer electrical environment by reducing the chance that a shock or fault can occur.

You can make a difference too. Specify finger safe products whenever designing or installing new panels or machinery. - Example of Large Feeder feeding a Motor Control CenterSupplemental Reading (Papers):- Arcing Flash/Blast Review with Safety Suggestions for Design and Maintenance-The Use of Low Voltage Current-Limiting Fuses to Reduce Arc Flash Energy- Using Current-Limiting Fuses to Reduce Hazards Due to Electrical Arc- Flashes-Recommend split into 2 smaller feeders for two reasons: 1) Reduces the wire size (higher impedance, lower fault current) 2) Reduces the OCPD size by splitting the load of of large mains and feeders into more than one circuit.

The smaller the device the better. Smaller device will sense faults quicker. With current limiting devices the smaller the device the better the current limitation

- Since the OCPDs in this type of design will not limit the short circuit current, other means to limit the available short circuit current will be needed- Suggest the use of high impedance components such as high impedance transformers or current limiting bus to limit the available short circuit current.

- The bus structure in Panelboards, Switchboards, and Motor Control Centers are only tested to 3 cycles- As seen before, Short Time Delays can be dangerous. Short Time Delays purposely leave the full extent of fault current flowing for a preset amount of time. This time is usually over several cycles (six to 30 cycles).- If selective coordination is the reason for using short time delays, this can be achieved using other types of devices. 2:1 ratio with Low Peak Fuses or using CBs with zone interlock.

- With the Current limiting design the OCPDs can do what they are intended to do.- If the fault current is in the current limiting range of the OCPD, the OCPD will limit the available short circuit current and time, thus reducing the arcing fault energy released. There are current-limiting overcurrent protective devices that have different degrees of current limitation. The higher the degree of current limitation, the greater the reduction in the energy let-thru that is possible when a higher magnitude fault occurs. The fuses types that are the most energy limiting are J,CC, T, RK1, & L. The Class RK5 fuses are current limiting, but not to the degree of Class J, CC, T and RK1 fuses.Renewable and One Time Fuses, which are class H, are not considered to be current limiting and are not recommended.

- There are some CBs that are current-limiting. Typically these CBs are at K5 current limiting level at best and usually not even that level of protection. If a current limiting CB is considered, it would be advisable to compare the let-thru values to the various fuse classes.

LIMIT THE CURRENTRequest Bussmann LOW-PEAK Class L, Class RK-1, Class J, and Class CC current limiting fuses.To minimize arc-flash and arc-blast energy hazardsproperly sized to provide Type 2 coordinated motor starter protection

With current limiting overcurrent protective devices, generally the smaller the ampere rating, the better the degree of current limitation. So design your systems to use lower ampere rated overcurrent protective devices. Look at the let-through for this example.This is an example of using lower ampere rated devices for motor circuit protection. - Type 2 protection guarantees NO DAMAGE to the motor starter and is backed by testing- No Damage to starter creates a better working environment since device is protectedThe allowable damage for a UL508 listed starter is similar to Type 1 damage level. With Type 1 level protection the starter heaters are permitted to rupture and the contacts permitted to disintegrate. If a worker is working in the enclosure when a fault occurs on the loadside of a Type 1 starter, the worker could be severely injured from the byproducts of the starter failing. Inherently, Type 2 protected starters require lower levels of let-through energy, and therefore provide for a safer installation than a Type 1 protected starter.

- With the current limiting design, low impedance components can be used. Greater probability OCPD will be in current limiting range. - With low impedance components the system will have:Better Voltage RegulationPower Losses are Minimized

Supplemental Reading:

- Arcing Flash/Blast Review with Safety Suggestions for Design and Maintenance-The Use of Low Voltage Current Limiting Fuses to Reduce Arc Flash Energy- Using Current Limiting Fuses to Reduce Hazards Due to Electrical Arc Flashes

-Another consideration is how one designs his work. If proper design of work is considered one can have better safety results.

The following are principles to follow to provide a safer work environment.PLAN EVERY JOB - Take the time to prepare a work plan that considers all possible eventualities. Before you start the job, think about each step and try to visualize the potential for hazards.ANTICIPATE UNEXPECTED RESULTS - When thinking about a job, break each task into small steps. Understand that plans can change, so be ready to modify the plan if necessary. Make sure that everyone involved in the job is working according to the same plan. Whenever work is required near an electrical hazard, a written plan is needed to outline the scope of the job.USE PROCEDURES AS TOOLS - Procedures are the best way to help you prepare, execute, and complete the job. Like any tools, make sure procedures are maintained.IDENTIFY THE HAZARD - After your work plan is complete, review each step. Consider that the equipment might be perfectly safe under normal conditions and very unsafe when systems are not working properly. Also consider potential hazards that may be unrelated to electrical energy.ASSESS PEOPLES ABILITIES - Any person assigned to tasks associated with electrical energy must be qualified and trained for the job at hand. He, or she, must be able to identify electrical hazards, avoid exposure to those hazards, and understand the potential results of all action taken. USE THE RIGHT TOOL FOR THE JOB - Use the appropriate tools for the job at hand, keep them accessible and in good working condition. Using a screwdriver for a job that requires a fuse puller is an invitation to an accident.ISOLATE THE EQUIPMENT - The best way to avoid an accident is to reduce exposure to the hazards present. Keep doors closed. Keep barricades in place. Install temporary voltage-rated blankets covering exposed live parts. PROTECT THE PERSON - Use the proper personal protection equipment for the job. This may include safety glasses or goggles,head protection, voltage-rated gloves, safety belts and harnesses or flame-resistant clothing.MINIMIZE THE HAZARD - If it is impossible to establish an electrically safe work environment, be sure to shut down every possible energy source. Understand that sometimes a de-energized circuit can become re-energized and to do something to lessen the risk.AUDIT THES PRINCIPLES - A principle is something you believe in enough to be willing to do. Review these principles often, add to them as needed.Each Employer is required to establish procedural requirements for safety-related work practices that includes a hazard evaluation process.Hazard/Risk Analysis evaluation procedure:Taking the time to plan the task to be performed provides, an opportunity to prevent accidents before they happenThe Hazard Risk Analysis promotes understanding, acceptance, and implementation of Electrical Safe Work PracticesThe Hazard Analysis also identifies opportunities for determining the level of job planning requiredhelps to avoid exposure to known hazardsdetermine safety issues impacted by the designselection of Personal Protective EquipmentThe 2002 NEC has a new arc flash labeling requirement.Read the requirement.This is a close-up of an example warning label this label warns of both arc flash and shock hazards plus reminds workers to use proper PPE. PPE stands for Personal Protection Equipment. 110.16 only requires the label to warn of arc flash hazard.

The type of equipment specified in 110.16 that is likely to be worked on as described is required to have a field affixed arc flash warning label. This will serve as a reminder to qualified workers that a serious hazard exists, that they or their management must assess the risk prior to approaching the hazard. Also it should remind them that they must follow the work practices for the level of hazard they may be working on or near. 110.16 only requires that this label state the existence of an arc flash hazard. It is suggested that the party responsible for the label include more information on the specific parameters of the hazard. In this way the qualified worker and his/her management can more readily assess the risk and better ensure proper work practices, PPE and tools. The specific additional information that should be added to the label includes items shown on this label. (next slide)((click) denotes certain points where it is suggested to left mouse click or enter or page down to synchronize with the slide animation.)

(click)Flash Protection Boundary(click)Incident energy at 18 inches expressed in cal/cm2(click)PPE required(click)Voltage shock hazard(click)Limited shock approach boundary(click)Restricted shock approach boundary(click)Prohibited shock approach boundary

This example label shown includes more of the vital information that fosters safer work practices. You can see that the detailed information is a greater aid to workers. Warning labels with this detail provide vital information specific to the particular equipment installation. The information quantifies the electrical shock and arch flash hazards for the specific equipment noted. Informative labels communicate to a qualified worker and his management vital parameters that are needed to fulfill safe work practices. If you are unfamiliar with some of the terminology on this label, it is suggested you get the Bussmann Safety Basics Handbook and/or NFPA 70E. The arc flash labeling requirement is intended to help reduce injuries and deaths. While not a requirement in the National Electrical Code, we feel it is important to cover some important regulations in OSHA and requirements in NFPA 70E related to working on live equipment.OSHA regulations state in 1910.333 (a) that workers should not work on live equipment (greater than 50 volts) except for one of two reasons:1. Deenergizing introduces additional or increased hazards (such as cutting ventilation to a hazardous location) or 2. Infeasible due to equipment design or operational limitations (such as when voltage testing is required for diagnostics).

Note: NFPA 70E Electrical Safety Requirements for Employee Workplaces 2000 in Part II 2-1.1.1 states essentially the same requirement.

However, when it is necessary to work on equipment live, it is necessary to follow safe work practices, which include assessing the risks, wearing adequate personal protection equipment and using the proper tools. The warning label of 110.16 helps facilitate this practice.

Until equipment is put into a safe work condition the equipment is considered to be live. NFPA 70 E Part II 2-1.1.3 provides the procedural steps for placing equipment in a safe work condition. One of the latter steps in this procedure is a voltage test of each phase conductor to verify they are deenergized. The worker performing this voltage testing must assume the equipment is live and therefore must wear appropriate personal protection equipment for the hazard assessed.

Summarize what was presented in this presentationShock BoundariesFlash Protection BoundariesIncident EnergyAppropriate PPE for the specific assessed hazardDesign suggestion to reduce the risk