why grounding is used-8th vis rc

BOARD OF ELECTRICAL ENGINEERINGINSTITUTE OF INTEGRATED ELECTRICAL

ENGINEERS OF THE PHILIPPINES, INC.

Why GROUNDING!!!Is Used?

Jaime V. Mendoza, PEE, MTMJaime V. Mendoza, PEE, MTM

Board MemberBoard Member

8th Visayas IIEE Region VII Conference 2007Cebu International Convention Center

Mandaue City, Sept. 28-29, 2007

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Why Grounding is Used? BOARD OF ELECTRICAL ENGINEERING

8th Visayas IIEE Region VII Conference – Sept. 28, 2007

INSTITUTE OF INTEGRATED ELECTRICAL ENGINEERS OF THE PHILIPPINES, INC.

TERMINOLGY

In Britain people have “earth” and in North America they have “ground”.

They are exactly the same thing, only different terms are used in different countries.

For example: Earth Leakage Circuit Interrupter and Ground-Fault Circuit Interrupter

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Why Grounding is Used?

To limit voltage imposed by

1. Lightning

2. Line surges

3. Unintentional contact with higher voltage lines

Stabilize the voltage to ground during normal operations.

Facilitate overcurrent device operation in case of ground fault on a solidly grounded system.

PEC- 2000 Section 2.50.1.2(a)

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To limit the voltages imposed by lightning or line surge

PEC-2.50.1.2(a)

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To limit the voltages imposed by lightning or line surge

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Facilitate overcurrent device operation in case of ground fault

Metal parts of premises wiring are bonded to an effectiveground-fault current path that has sufficiently low impedanceto quickly clear line-to-case faults by opening the circuit protection device.

240V240V

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Earth is Not an Effective Ground-Fault Current Path

I = E/R, E = 240V, R = 25 , I = 240/25 = 9.6 AInsufficient current to trip overcurrent protection device

240

9.6

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Ground Fault Circuit Interrupter

GFCI – A device intended for the protection of personnel that functions to deenergize a circuit or portion thereof within an established period of time when a current to ground exceeds the values established for a device.

The GCFI does not protect someone against receiving an electrical shock, but it does limit the time hazards exists. Hazard exist only during period of time fault is there.

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GCFI CAN ELIMINATE THIS!


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A GFCI is designed to protect persons against electric shock.It operates on the principles of monitoring the unbalanced currentBetween the ungrounded and the grounded neutral conductor.

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GFCI Protection for Personnel1. Dwelling Bathroom Receptacle

and /or 250 V

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GFCI Protection for Personnel2. Dwelling Garage Receptacle

[Sec. 2.10.1.8(a)(2)Ex 1]

All 15/20A, 125/250V receptacles installed in a

dwelling unit garage must have GFCI protection.

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GFCI Protection for Personnel2. Dwelling Garage Receptacle

All 15 and 20 A, 125/250 V receptacles in accessory

buildings and similar work areas must be GFCI protected.

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GFCI Protection for Personnel3. Dwelling Outdoor Receptacle

Section 2.10.1.8(3)

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GFCI Protection for Personnel4. Dwelling Basement Receptacle

All 15/20A, 125/250V receptacles in unfinishedareas of basements must be GFCI protected.

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GFCI Protection for Personnel5. Dwelling Unfinished Basement

All 15/20A, 125/250V receptacles in unfinishedAreas of basements must be GCFI protected.

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GFCI Protection for Personnel6. Kitchens for Countertop Appliances

All 15/20A, 125/250V, receptacles thatserve dwelling unit kitchen countertopsurfaces must be GFCI protected.

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GFCI Protection for Personnel6. Dwelling Laundry or Utility Sink

All 15/20A, 250V receptacles located within 6 ft or 1.8 m of a laundry or utility sink must be GFCI protected.

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GFCI Protection for Personnel7. Dwelling Wet Bar Sinks

GFCI protection required

if within 1.8 m of sink

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PEC 2000- Section 2.10.1.8 (a)

a) Dwelling Units 1. Bathrooms

2. Garages 3. Outdoors 4. Crawl spaces at or below grade

level 5. Unfinished

basements 6. Kitchens for

countertop appliances 7. Wet bar sinks

GFCI Protection for Personnel

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Electric Shock Severity

1. Path of Current through Body

2. Length of Time Current Flows

3. Amount of Current through Body

Electric Shock

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Effects of AC Electric Shock

RMS Current Effects

1- 5 mA Threshold of sensation

10-20 mA Involuntary muscle contractions

20-100 mA Pain, breathing difficulties

100 - 300 mA Ventricular fibrillation, possible death

> 300 mA Respiratory paralysis, burns, unconsciousness

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Identification of Equipment Grounding Conductors

PEC 2.50.6.10

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But, for a grounding conductor larger than No. 6 AWG or 14 mm2, an insulated conductor of other than green color or green with yellow stripes may be used provided one of the following steps is taken: PEC-2.50.6.10(a)

1. Stripping the insulation from an insulated conductor of another color (say black) for the entire length that is exposed on the box or other enclosure so that the conductor appear as a bare conductor.

2. Painting the exposed insulation green for its entire length within the enclosure.

3. Wrapping the entire length of exposed insulation with green-colored tape or green-colored

adhesive labels.

Identification of Equipment Grounding Conductors

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Sizing Equipment Grounding Conductors (Sec. 2.50.6.13)

The regulations for calculating the size of equipment grounding conductor are:1. Table 2.50.6.13 shall be used to size the equipment

conductor. ( Based on the rating of the protective device ahead of the equipment.)

2. When ungrounded conductors are increased in size and an equipment grounding is installed with them, the equipment grounding conductor is required to be proportionately increased in size according to the circular mil area of the ungrounded conductors.

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Sizing Equipment Grounding Conductors

The regulations for calculating the size of equipment grounding conductor are:3. Where more than one circuit is installed in a

single raceway or cable, one equipment grounding conductor can be installed in the raceway or cable; it will be sized for the largest overcurrent device protecting conductors in the raceway or cable.

4. An equipment grounding conductor not smaller than 18 AWG copper(0.75 mm2) is permitted for flexible cords when the flexible cord is protected at or over 20 amperes.

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The regulations for calculating the size of equipment grounding conductor are:5. The equipment grounding conductor is never

required to be larger than the circuit conductors.

6. Where the overcurrent protection is an instantaneous circuit breaker or a motor protector, the equipment grounding conductor is sized according to the size of the motor overload protective device.

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The regulations for calculating the size of equipment grounding conductor are:7. When conductors are run in parallel in more

than one raceway or cable , as permitted in Sec. 3.10.1.4, the equipment grounding conductor is run in parallel. Each of the paralleled equipment grounding conductors is sized according to the ampere rating of the overcurrent device protecting the conductors in the raceway or cable.

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Section 2.50.6.9

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European Coloring

Ground wire – green wire with yellow stripe color

Neutral wire – blue color

Live wire – brown

black and black with white strip (for 3-

phase)

European Coding of Grounded Conductor

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In the US, Black is the hot wire, white is the neutral or common wire and green is the equipment grounding.

US Coding of Grounded Conductor

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The basic rule in PEC- 2.1.1.6(a) requires the grounded conductor Sizes 14 mm2 or smaller to be identified by:

1. A white color

2. A gray color

3. Three continuous white stripes, on other than green insulation, extending

along the entire length of the conductor

Prior to the PEC-2000 Code, the gray color was permitted to be used as a hot conductor.

Means of Identifying Grounded Conductor

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This means that you can use either white or gray to identifythe grounded neutral conductor of a single wiring system


PEC 2.1.1.6(a)

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PEC 2.1.1.6(a)

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Insulated grounded conductor larger than 6 AWG or 14 mm2 to be identified by the one of the following methods: PEC 2.1.1.6(b)

1. By a white or gray outer finish

2. By three continuous white stripes, on other than green insulation, running along the entire length of conductor

3. By a distinctive white marking ,encircling the conductor, placed there at the

time of installation, and the identifying the grounded conductor at each

termination (The identification may be by tagging, marking, painting or other effective means)


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Identifying Grounded Neutral Conductors of Different Systems

PEC 2.1.1.6(d)

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When sizing electrical conductors, the ampacity of the main consideration. This is not the case when sizing electrode conductor, it is sized according to cross-sectional area of the service-entrance conductor.

The size of the grounding electrode conductor is taken directly from Table 2.50.3.1.17 of PEC, when the size of the service entrance conductors is not larger than 1100 kcmil cu. Or 1750 kcmil aluminum.

Sizing the AC Grounding Electrode Conductors

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When the service entrance conductors are larger than 1100 kcmil copper or 1750 kcmil aluminum, the grounded conductor shall be 12 ½ % of the largest phase conductor.


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What are the sizes of the grounding electrode conductors of the following if the service entrance conductors used are:

1. 500 kcmil copper

2. 500 kcmil aluminum

3. 1/0 copper

4. 2 copper

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Installation of Grounding Rods

Basic Requirements for a rod or pipe electrode are: Section 2.50.3

1. Minimum length of 2.5 m or 8 ft

2. When metal pipe or conduit is used for electrode, it is required to be not smaller than trade size ¾ conduit.

3. Iron or steel pipe electrodes are required to have a galvanized surface or other corrosive resistant material.

4. Rod electrode may be iron, steel, or stainless steel and are required to have a minimum diameter of 5/8 inch (16mm) diameter.

5. Nonferrous rods, or their equivalent are required to have a minimum diameter of ½ inch (13 mm).

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Installation of Grounding Rod

Section 2.50.13.15(G)*

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Main Bonding Jumper

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Main Bonding Jumper

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Bonded

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Sizing the Main Bonding Jumper (Sec. 2.50.2.9(d))

Three methods for sizing the main bonding jumper are given in Table 2.50.3.17.

When sizing the main bonding jumper, the size and material of service entrance conductors and material used for the main bonding conductor are taken into consideration.

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Sizing the Main Bonding Jumper

Three methods for sizing the main bonding jumper are:1. Basic Rule: Use Table 2.50.3.17, the

grounding electrode conductor table, is also used for the main bonding jumper.

2. 12 ½ Percent Rule for Large Conductors. When the total circular area of any service entrance phase conductor exceeds the maximum circular-mil area listed in Table 2.50.3.17, the main bonding jumper shall not be smaller than 12 ½ % of the service phase conductors.

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Sizing the Main Bonding Jumper

Three methods for sizing the main bonding jumper are:

3. Rule for Using Different Materials. This rule applies when the main bonding jumper is a different material than the service-entrance conductors. One could be aluminum and the other copper for example. In this case, the minimum size of the main bonding jumper is based on assuming that the service entrance conductors are of the same material as the main bonding jumper and that ampacity is equivalent to the installed phase conductors.

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Sizing the Main Bonding Jumper (Sec. 2.50.5.13(c))

325 mm2 conductors

2.50.5.13, Table 2.50.3.1750 mm2 EquipmentBonding Jumper

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What is Effective Grounding?

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Effective Grounding

A violation of PEC Art. 2.50.3.11 which prohibits using the same grounding electrode for a lightning rod system and a system supply.

VIOLATION!!!

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Effective Grounding

PEC Art. 250.5.17 Lightning Protection System. The bonding of a system grounding electrode and a lightning rod grounding electrode.

BONDING

REQUIRED!!!

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Effective Grounding

When different grounding electrodes are used for abuilding and are not bonded together, a voltage hazard will exist!!!

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Older designs, have independent grounding systems.

The more recent trend is to bond all the ground systems.

Effective Grounding

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How surges enter facilities

Effective Grounding

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Understanding the Lightning DischargeCloud electrification –

charge particle separation, quasi static

E Field est. between cloud & ground

Downleader approaches, E Field increases to point of

initiation of upward streamers

Upward leader propagates toward

downleader to complete ionised path between

cloud & ground

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Effective Grounding

Section 2.50.5.17

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Effective Grounding

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Effective Grounding

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Why Ground Noncurrent-Carrying Conductive Materials Enclosing Electrical Equipment?

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Why Ground Noncurrent-Carrying Conductive Materials Enclosing Electrical Equipment?

EQUIPMENT GROUNDING

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Potential Difference

Potential difference between a grounded

water pipe and an ungrounded motor.

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Motor ground-fault. A hazard now exists.

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The hazard results in an electric shock.

There is a Voltage!

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Another shock hazard exists.

There is a Voltage!!

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Shock hazard eliminated by installing

a bonding jumper.

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Neutral Conductor (PEC2.50.2.17(b))

The neutral conductor from the neutral point of the transformer or the generator to its connection point to the grounding impedance shall be fully insulated.

The neutral conductor shall have an ampacity of not less than the maximum current rating of the grounding impedance. In no case shall the neutral conductor be smaller than 8.0 mm2 copper or 14 mm2 aluminum or copper-clad aluminum.

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Neutral Conductor (PEC 2.50.2.17(b))

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Grounded Conductor

Not a “neutral” because it is not a 3 0r 4 wire system.

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Grounded Conductor

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Grounding and bonding at the service equipment

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why grounding is used-8th vis rc

Documents

electrical shock

visayas iiee region

case of ground fault

circuit protection device

gfci protection

period of time fault

protection of personnel

overcurrent device operation