Question 1

What size equipment grounding conductor do I need for a 100A breaker?

Accepted Answer

Per NEC Table 250.122, a 100A overcurrent device requires a minimum 8 AWG copper or 6 AWG aluminum equipment grounding conductor. If circuit conductors are adjusted in size for voltage drop, the EGC must be increased proportionally per NEC 250.122(B).

Question 2

How do you size a grounding conductor by overcurrent device rating?

Accepted Answer

Use NEC Table 250.122 and match the rating of the automatic overcurrent protective device (fuse or breaker) ahead of the circuit. For example: 15A = 14 AWG Cu, 60A = 10 AWG Cu, 200A = 6 AWG Cu, 400A = 2 AWG Cu, 1000A = 3/0 AWG Cu. Do not size based on load current—only the OCPD rating.

Question 3

Does system voltage affect grounding conductor size?

Accepted Answer

No. NEC 250.122 specifies equipment grounding conductor size only by the rating of the overcurrent device protecting the circuit, not the system voltage. Whether your system is 120V, 240V, 277V, or 480V, a 200A breaker still requires a 6 AWG copper EGC. Voltage matters for insulation rating, not conductor size.

Grounding Selector

System Input

Result

Reference — NEC Table 250.122

How It Works