EGC Sizing Calculator (NEC Table 250.122)

Size the minimum equipment grounding conductor from upstream OCPD rating per NEC Table 250.122 for copper or aluminum.

  1. Set NEC edition Choose the in-force NEC edition used by your AHJ for plan review and inspection.
  2. Enter OCPD rating Input the branch or feeder OCPD ampere rating that protects the circuit.
  3. Choose conductor material Pick copper or aluminum to read the matching minimum EGC size from Table 250.122.
  4. Apply upsizing rules if needed If ungrounded conductors were upsized for voltage drop, proportionally increase EGC size per 250.122(B).

How do I size an equipment grounding conductor from breaker size?

Use NEC Table 250.122 and select the row at or above the OCPD rating. Then read the copper or aluminum column for the minimum EGC size.

Is EGC size based on load amps or breaker amps?

It is based on the rating of the OCPD protecting the circuit, not the calculated load current.

Do I have to upsize the ground wire when I upsize phase conductors?

Usually yes. NEC 250.122(B) requires proportional EGC upsizing when ungrounded conductors are upsized for voltage drop.

Can I run aluminum EGC in conduit feeders?

Yes where permitted by installation conditions and terminations. This calculator returns aluminum minimums alongside copper so you can compare both options.

What if multiple circuits share one raceway?

NEC 250.122(C) allows a single EGC sized for the largest OCPD in that raceway, with conditions. Verify raceway-sharing details before finalizing.

Does this tool size grounded neutrals too?

No. It only sizes equipment grounding conductors. Neutral sizing follows different NEC rules and load-calculation methods.

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