Grounding and Bonding

Question 1

Steps to determine the minimum size copper grounding conductor to water pipe.

Answer 1

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

2. Then size from Table 250.66

Example 4 parallel 500kcmil conductors = 2000Kcmil x .125 = 2500Kcmil

250.66 over 1750Kcmil = 3/O grounding conductor

Question 2

Minimum size copper grounding electrode conductor to the ground rod

Answer 2

250.66
Not required to be larger than size #6 AWG

Question 3

Minimum size MAIN Bonding Jumper permitted in the disconnect enclosure.

Answer 3

1. 250.28(D) minimum sized using Table 250.102(C)–Unless, the conductor size EXCEEDS the size listed in the table.
2. If larger, multiply cmils by 12 1/2% (.125)
3. .125 X largest service conductor

Question 4

Minimum size copper bonding jumper to each of the Metal Service Raceways

Answer 4

1. required to be NOT smaller than specified in Table 250.102
2. If larger than maximum size listed, the miinimum size is .125 X the cmils of largest cable in raceway.

cmils = Chapter 9, Table 8

Question 5

Sizing Equipment Grounding

Answer 5

1. Determined by 250.122
2. 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

Question 6

Voltage Drop Adjustments

The size of a conductor will affect the amount of current that will flow

Answer 6

1. Table 8 look up cmil area
2. divide largest by smallest
3. look up minimum size equipment grounding conductor
4. Table 8: 100A =16,510 cmil
5. 16,510 cmil X 1.26 = 20,803
6. 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

Question 7

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:

Answer 7

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.

Question 8

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:

Answer 8

4AWG

1. Table 8, CH 9

1/0 = 105,600 cmil
3/0 = 167,800 cmil
105,600/167,800 = 1.59

2. Minimum size EGC - 150A is Table 250.122 = 6AWG

6AWG = 26,240cmil x 1.59 = 41,696 cmils

3. Table 8 = 41,696 = 4 AWG

Question 9

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:

Answer 9

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.

Question 10

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.

Answer 10

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.