What is NEC Table 250.122?

NEC Table 250.122 is the National Electrical Code table that specifies the minimum size of equipment grounding conductors (EGCs) based on the ampere rating of the overcurrent protective device (breaker or fuse) protecting the circuit. It covers both copper and aluminum conductors.

What is an equipment grounding conductor (EGC)?

An EGC is the green or bare wire that connects metal enclosures, conduit, and equipment frames back to the service panel ground. It provides a low-impedance fault path so a breaker trips quickly during a ground fault, protecting against electric shock and fire.

Can I use a smaller ground wire if I upsize the circuit conductors?

No — if you increase the phase conductor size beyond what the breaker rating requires, NEC 250.122(B) requires you to proportionally increase the EGC as well. This calculator uses the breaker rating as the base; consult 250.122(B) separately if you have upsized conductors.

Is aluminum allowed for equipment grounding conductors?

Yes. Aluminum and copper-clad aluminum EGCs are permitted by NEC 250.122. However, aluminum must not be installed in contact with masonry, earth, or where subject to corrosion, per NEC 250.64(A). Aluminum EGCs are one AWG size larger than copper for the same ampere rating.

What if my breaker is between two table values?

Per NEC rules, use the next higher ampere rating listed in the table. For example, a 90 A breaker is not explicitly listed; you use the 100 A row, which requires a 8 AWG copper EGC.

Does this replace a licensed electrician review?

No. This tool is for reference and planning only. Always have a licensed electrician review your installation and obtain required permits. Local codes may be more restrictive than the NEC.

Ground Wire Size Calculator

Name: Ground Wire Size Calculator
Availability: InStock
Author: Nham Vu

Enter your circuit breaker rating and conductor material to find the minimum ground wire size per NEC Table 250.122.

Circuit Parameters

Based on NEC Table 250.122

Overcurrent Device Rating (Amps)

Enter the breaker or fuse ampere rating protecting this circuit.

Conductor Material

Copper

Most common

Aluminum

Copper-clad also

Common Breaker Sizes

Result

Minimum EGC per NEC Table 250.122

Enter a breaker rating and click Calculate.

NEC Table 250.122 — Full Reference

Minimum size equipment grounding conductors for grounding raceways and equipment

Breaker / Fuse (A)	Copper AWG	Aluminum AWG

Summary

Enter your circuit breaker rating and conductor material to find the minimum ground wire size per NEC Table 250.122.

How it works

Enter the circuit breaker or fuse ampere rating for the circuit.
Select conductor material: copper or aluminum/copper-clad aluminum.
The calculator looks up NEC Table 250.122 and returns the minimum EGC size.
Review the result showing AWG gauge, cross-sectional area, and the applicable table row.
For breakers not in the table, the next higher listed value is used per NEC rules.

Use cases

Verify the correct ground wire size for a new circuit installation.
Size equipment grounding conductors for sub-panels and branch circuits.
Confirm compliance with NEC 250.122 before rough-in inspection.
Compare copper vs. aluminum EGC options for cost planning.
Determine grounding wire gauge for HVAC, appliance, and EV charger circuits.
Double-check existing wiring during home inspection or service upgrades.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu