TradesHow this works
Two conductors get confused all the time. The equipment grounding conductor is sized from the breaker in Table 250.122. The grounding electrode conductor is sized from the service in Table 250.66, and then the electrode reductions let it shrink. This tool runs whichever one you pick and, for the electrode conductor, shows both the full table size and the smaller size the electrode actually allows.
The reduction is where the savings hide. A 200 amp service takes a large electrode conductor by the table, but a run to a ground rod need not be larger than 6 AWG copper.
Common questions
What is the difference between the EGC and the GEC?
The equipment grounding conductor bonds the metal of equipment back to the panel and is sized from the breaker rating in Table 250.122. The grounding electrode conductor connects the system to the earth electrode and is sized from the service conductors in Table 250.66. They are different conductors with different tables.
Why can a small wire go to a ground rod?
Because a ground rod can only carry so much current into the earth, NEC 250.66(A) says the grounding electrode conductor to a rod, pipe, or plate need not be larger than 6 AWG copper. A concrete-encased Ufer caps at 4 AWG copper. So even a large service often only needs a 6 AWG conductor to the rod.
Do I upsize the EGC if I upsize the circuit wire?
Yes. When you increase the ungrounded conductors in size, for voltage drop for example, NEC 250.122(B) requires the equipment grounding conductor to be increased by the same circular-mil ratio.
Sources: NEC Table 250.122 equipment grounding conductor (2023) · NEC Table 250.66 and 250.66(A)/(B)/(C) grounding electrode conductor (2023). Engine version 1.0.0. Risk tier 2.