Equipment Grounding Conductor

DOE-HDBK-1092-98

4.10 EQUIPMENT GROUNDING CONDUCTOR

Equipment grounding conductors for ac systems, where used, should be run with the conductors of

each circuit per NEC Section 250-57(b).

Earth and the structural metal frame of a building may be used for supplemental equipment bonding,

but they shall not be used as the sole equipment grounding conductor for ac systems per NEC Sections

250-58 and 250-51.

For circuits having paralleled conductors in multiple metal raceways, an equipment grounding

conductor shall be run in each raceway. The size of each paralleled equipment grounding conductor

is a function of the rating of the circuit overcurrent protection. (See NEC Sections 250-95 and

310-4.)

4.10.1 SIZING THE EQUIPMENT GROUNDING CONDUCTOR

NEC Section 250-95 lists the requirements for calculating the size of the equipment grounding

conductors in an electrical circuit. There are basically five steps to be applied in sizing, selecting, and

routing the equipment grounding conductors:

1. NEC Table 250-95 shall be used to size the equipment grounding conductor.

2. When conductors are run in parallel in more than one raceway, the equipment grounding

conductor is also run in parallel.

3. Where more than one circuit is installed in a single raceway, one equipment grounding

conductor may be installed in the raceway. However, it must be sized for the largest overcurrent

device protecting conductors in the raceway.

4. When conductors are adjusted in size to compensate for voltage drop, the equipment grounding

conductor shall also be adjusted in size.

5. The equipment grounding conductor is never required to be larger than the circuit conductors.

For example: What size THWN copper equipment grounding conductor is required to be run in a

raceway with a 70 A overcurrent protection device protecting the circuit?

Step 1:

Finding EGC--NEC Table

250-95 70 A OCPD requires #8 copper

Answer:

The equipment grounding conductor is required to be at least #8 THWN copper.

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