Which conductor size is specified for the equipment grounding conductor of a 70-amp circuit?

Which conductor size is specified for the equipment grounding conductor of a 70-amp circuit?

• A. 8 AWG
• B. 6 AWG
• C. 4 AWG
• D. 10 AWG

Answer: (A)

The key idea is that the equipment grounding conductor (EGC) size is chosen from NEC Table 250.122 based on the rating of the overcurrent device. The EGC must be large enough to carry the fault current back to the source so the protective device can trip quickly, but it does not have to carry normal load current. For a circuit protected at 70 amps, the table specifies a minimum of 8 AWG copper for the equipment grounding conductor. That means an 8 AWG copper EGC satisfies the requirement, and is the smallest size that meets the code. Using 6 AWG or 4 AWG would also be acceptable (larger conductors are allowed), but 10 AWG would be undersized for a 70 A OCPD and would not meet the minimum.

The key idea is that the equipment grounding conductor (EGC) size is chosen from NEC Table 250.122 based on the rating of the overcurrent device. The EGC must be large enough to carry the fault current back to the source so the protective device can trip quickly, but it does not have to carry normal load current.

For a circuit protected at 70 amps, the table specifies a minimum of 8 AWG copper for the equipment grounding conductor. That means an 8 AWG copper EGC satisfies the requirement, and is the smallest size that meets the code. Using 6 AWG or 4 AWG would also be acceptable (larger conductors are allowed), but 10 AWG would be undersized for a 70 A OCPD and would not meet the minimum.