Grounding and Bonding Flashcards
Steps to determine the minimum size copper grounding conductor to water pipe.
Table 250.102 (Note 1)
1. In the case of multiple sets of service conductors (parallel), specifies the total cross-section area of each phase as 4X
- Then size from Table 250.66
Example 4 parallel 500kcmil conductors = 2000Kcmil x .125 = 2500Kcmil
250.66 over 1750Kcmil = 3/O grounding conductor
Minimum size copper grounding electrode conductor to the ground rod
250.66
Not required to be larger than size #6 AWG
Minimum size MAIN Bonding Jumper permitted in the disconnect enclosure.
- 250.28(D) minimum sized using Table 250.102(C)–Unless, the conductor size EXCEEDS the size listed in the table.
- If larger, multiply cmils by 12 1/2% (.125)
- .125 X largest service conductor
Minimum size copper bonding jumper to each of the Metal Service Raceways
- required to be NOT smaller than specified in Table 250.102
- If larger than maximum size listed, the miinimum size is .125 X the cmils of largest cable in raceway.
cmils = Chapter 9, Table 8
Sizing Equipment Grounding
- Determined by 250.122
- When run in parallel in separate raceways, an equipment grounding conductor is required to be run in each raceway. It is required to be sized based on the Feeder Overcurrent device- 250.122(F)
Example:2 sets of parallel 1/O copper coductors and terminate in separate rigid non-metal raceways. The feeder is protected by 300A overcurrent device. 250.122, 300 (copper) = #4 AWG equipment grounding wire
Voltage Drop Adjustments
The size of a conductor will affect the amount of current that will flow
- Table 8 look up cmil area
- divide largest by smallest
- look up minimum size equipment grounding conductor
- Table 8: 100A =16,510 cmil
- 16,510 cmil X 1.26 = 20,803
- Minimum size for 20,803 cmil = 6 AWG, Table 250.122
Assume a feeder consists of size 3 AWG copper run in rigid nonmetallic c
A feeder protected by 800A fuses is run from one part of a building to another under the floor in 2 parallel sets of PVC with size 500 Kcmil copper RHW wires. The minimum size copper equipment grounding conductor permitted to be run in each conduit is:
1/0AWG
250.122(F)(1)(b)
Required an equipment grounding conductor to be run in each raceway sized using Table 250.122 to the rating of the feeder O.C. device.
The copper THWN wires for a 480V, 3 phase feeder protected 150A time-delay fuses are increased in size from the minimum required 1/0AWG to size 3/0 AWG to compensate for voltage drop. If the feeder is run in PVC, the minimum size copper equipment grounding conductor permitted to be for this feeder is:
4AWG
- Table 8, CH 9
1/0 = 105,600 cmil
3/0 = 167,800 cmil
105,600/167,800 = 1.59
- Minimum size EGC - 150A is Table 250.122 = 6AWG
6AWG = 26,240cmil x 1.59 = 41,696 cmils
- Table 8 = 41,696 = 4 AWG
A transformer supplies a 200 ampere panelboard with 120/240 volt single-phase power. The secondary conductors from the transformer to the panelboard are size 3/0 AWG
copper. This transformer is near the service disconnect for the building, and it is grounded
to the same metal underground water pipe as the service. The minimum size copper
grounding electrode conductor permitted for this transformer installation is:
4 AWG
Section 250.30(A)(2) requires that the grounding electrode conductor be sized according
to the maximum size ungrounded conductor supplied by the separately derived system
(3/0 AWG copper) using Table 250.66.
A common bonding grid for a permanent swimming pool is formed by connecting together
with a bonding wire all metal parts associated with the pool such as metallic parts of the
pool structure, forming shells, mounting brackets of lighting fixtures, metal ladders, and
other metal attached to the pool, metal equipment associated with the water circulating
system, pool covers and similar metal parts. The conductor used for this bonding is:
A. required to be solid copper not smaller than size 8 AWG.
B. permitted to be solid aluminum if insulated and not smaller than size 8 AWG.
C. required to be insulated copper, stranded, and not smaller than size 8 AWG.
D. permitted to be bare, insulated, or covered copper not smaller than size 6 AWG.
E. required to be copper not smaller than size 2 AWG.
A 8 AWG, solid copper, insulated, covered, or bare.
680.26(B) Equipotential Bonding
The conductor used as a part of the main bonding grid is required to be copper, not
smaller than 8 AWG, and either insulated, covered, or bare as long as it is a solid
conductor.
Table 250.66
shall be used to size the grounded (neutral)
conductor, the grounding electrode
conductor, main bonding jumper, and
all system bonding jumpers, where
there is not an overcurrent protection
device ahead of the conductors and
equipment served.
Table 250.66.
The procedure for
selecting
the grounding electrode
conductor
to connect the service to a
metal water pipe is determined by the
size of the service-entrance conductors
per Table 250.66.
Finding size GEC
Table 250.66
250 KCMIL = 2 AWG cu.
Test takers should
note that the grounding electrode
conductor used to connect the service
to a rod electrode does not have to be
sized larger than 6 AWG copper per
250.66(A).
250.66(A)
when sizing the GEC that is to be connected to a driven rod, see:
250.66(A). For concrete encased, see
250.66(B), and for a ground ring, see
250.66(C).
What size grounding electrode conductor is required for a ground ring with 400 KCMIL copper service-entrance conductors?
Step 1: Finding grounding conductor
250.52(A)(4) and 250.66(C)
2 AWG cu. electrode requires 2 AWG cu.
Solution: The grounding electrode is 2 AWG copper.
The size of supply-side
bonding jumpers and the main bonding
jumper is based on the size of the service
conductors
per Table 250.102(C)(1) and
Note 1 up to 1100 KCMIL copper or
1750 KCMIL aluminum and 12-1/2
(0.125) percent for sizes larger than that.
SBJ & MBJ 250.102(C)(1)
EQUIPMENT BONDING JUMPER
ON LOAD SIDE OF AN OVERCURRENT DEVICE
250.102(D)
To size equipment bonding jumpers on the load side of the overcurrent protection
devices downstream from the service, use Table 250.122. The bonding jumper shall be a
conductor sized according to Table 250.122 for the largest overcurrent protection device
supplying the electrical circuits. If the bonding jumper supplies two or more raceways or
cables, the same rules apply and a full-size equipment bonding jumper shall be selected.
Note, it is not necessary to size the equipment bonding jumper larger than the ungrounded
(phase) conductors, but in no case should it be smaller than 14 AWG per 250.102(D).
ISOLATED RECEPTACLES
250.146(D)
An isolated equipment grounding conductor shall be used to connect the isolated
ground receptacle terminal back to the grounding connection at the service equipment
or separately derived system to reduce electromagnetic interference.
This rule applies where electrical noise (known as electromagnetic interference) occurs
in the grounding circuit. To help prevent such noise, an insulated equipment grounding
conductor shall be permitted to be run to the isolated terminal of an isolated ground
receptacle. This insulated grounding conductor shall be permitted to pass through one or
more panelboards and other metal boxes in the same building without being connected
to those panelboards as permitted in 408.40, Ex.
Note, it still has to terminate at the equipment grounding terminal at a separately derived
system or service panel. (See Figure 3-39)
Size 2/0 AWG, THWN, aluminum conductors are installed for a 150 ampere service. The minimum size copper grounding electrode conductor run to the water pipe for the service is:
A. 8 AWG. B. 6 AWG. C. 4 AWG. D. 3 AWG. E. 1 AWG.
B 6 AWG
This is a service entrance conductor and there is no overcurrent device on the supply end of the conductors. Base the grounding electrode conductor on the size and type of ungrounded conductors using Table 250.66.
MRC — E3503.4 and Table E3503.1
A 60 ampere rated circuit is run in rigid nonmetallic conduit using size 4 AWG, THHN, copper conductors. The minimum size copper equipment grounding conductor permitted to be run in the conduit with the circuit conductors is:
A. 10 AWG. B. 8 AWG. C. D. E. 6 AWG. 4 AWG. 2 AWG.
10 AWG
There is an overcurrent device at the supply end of the conductor so the equipment grounding conductor is sized from Table 250.122 based upon the rating of the overcurrent device which in this case is 60 amperes.
MRC — E3808.12 and Table E3808.12
A commercial service entrance with a 200 ampere main circuit breaker has size 3/0 AWG, THWN, copper service entrance conductors, and the service is grounded to a metal underground water pipe and a ground rod as the supplemental electrode. The minimum size copper grounding electrode conductor permitted to be run to the ground rod is:
A. 10 AWG. B. 8 AWG. C. D. E. 6 AWG. 4 AWG. 2 AWG.
6 AWG
250.66(A) only requires the grounding electrode conductor to a ground rod to be as large as an size 6 AWG copper where it only connects to the ground rod.
MRC — E3503.4 and Table E3503.1 Note d
