Equipment Grounding Conductor Size
Look up the minimum EGC size based on OCPD rating (NEC Table 250.122).
| Minimum EGC Size | 8 |
|---|---|
| OCPD Rating Used | 100 A |
· Based on NEC Table 250.122 for 100A OCPD.
· Minimum equipment grounding conductor: 8 AWG copper.
· If conduit or cable armor serves as the EGC, verify continuity and suitability.
· Always verify against the current edition of the NEC and local amendments.
How It Works
The equipment grounding conductor (EGC) provides the fault-current return path for metal raceways, enclosures, and equipment. Its size is based on the rating of the overcurrent protective device (OCPD) ahead of the circuit, per NEC Table 250.122. The EGC does not carry normal load current, only fault current, so it is sized differently from current-carrying conductors. If you are sizing a supply-side bonding jumper or grounding electrode conductor (GEC), different tables apply (NEC 250.66 or 250.102). Consult a licensed electrician for service entrance work.
Example
A circuit protected by a 100 A breaker requires a minimum 8 AWG copper EGC per NEC Table 250.122.
Frequently Asked Questions
Can I use the EGC as the neutral?
Only in certain limited cases (like at a separately derived system or at the main service) where the neutral and equipment ground are bonded. On branch circuits, always keep them separate.
Does this apply to EMT conduit?
EMT and other listed metallic raceways can serve as the EGC when properly connected. This calculator is for wire-type EGCs per Table 250.122.
What if I increase the conductor size above the minimum?
You must also increase the EGC proportionally when you upsize the phase conductors (NEC 250.122(B)).