Ground wire size calculator
Enter the breaker or fuse rating ahead of the circuit. You get the minimum copper or aluminum equipment grounding conductor and the row of Table 250.122 it came from.
Built on the 2026 NEC · Free, no sign-up · Updated October 2026
Result
10 AWG/kcmil copper
Table 250.122, the row used
- Rating or Setting of Automatic Overcurrent Protective Device (OCPD) in Circuit Ahead of Equipment, Conduit, Not Exceeding (Amperes)
- 60
- Size (AWG or kcmil) — Copper
- 10
- Size (AWG or kcmil) — Aluminum or Copper-Clad Aluminum
- 8
How it was calculated
- Locate the row in Table 250.122 where OCPD ≤ 60 A.
- Read the copper column: 10.
Assumptions
- OCPD rating 30 A → row "not exceeding 60 A".
- copper EGC selected from that row.
- Base lookup only — if the ungrounded conductors were upsized (e.g., for voltage drop), wire-type EGCs must be increased proportionally in circular mil area per 250.122(D). This tool does not apply that adjustment.
Sections used
These are the sections the calculator applies. Look them up in your code book before you rely on the result, and check the code your AHJ has adopted.
How the EGC is sized
The equipment grounding conductor (EGC) is sized from the rating of the overcurrent device protecting the circuit, not from the size of the hot conductors. Find the row in Table 250.122 for the device rating and read across to copper or aluminum. If your rating falls between rows, use the next row up.
The EGC never has to be larger than the circuit conductors it runs with (250.122(A)).
When the EGC has to be bigger
- Voltage drop: if you upsize the hot conductors for any reason other than ampacity derating, 250.122(D) requires a wire-type EGC to be increased by the same ratio of circular mil area.
- Parallel runs: each raceway or cable in a parallel set needs a full-size EGC based on the overcurrent device for the whole feeder, under 250.122(H).
- Motor circuits: special rules in 250.122(F) apply when the motor's short-circuit protection is an instantaneous-trip breaker or motor short-circuit protector.
EGC versus GEC
The equipment grounding conductor runs with the circuit and clears faults. The grounding electrode conductor connects the service or system to ground rods, the water pipe, or other electrodes. They come from different tables. For the GEC, use the grounding electrode conductor calculator.
Worked example
A circuit protected by a 30 A breaker, copper EGC:
- OCPD rating (amps): 30
- EGC material: Copper
Result
10 AWG/kcmil copper
Table 250.122, the row used
- Rating or Setting of Automatic Overcurrent Protective Device (OCPD) in Circuit Ahead of Equipment, Conduit, Not Exceeding (Amperes)
- 60
- Size (AWG or kcmil) — Copper
- 10
- Size (AWG or kcmil) — Aluminum or Copper-Clad Aluminum
- 8
How it was calculated
- Locate the row in Table 250.122 where OCPD ≤ 60 A.
- Read the copper column: 10.
Assumptions
- OCPD rating 30 A → row "not exceeding 60 A".
- copper EGC selected from that row.
- Base lookup only — if the ungrounded conductors were upsized (e.g., for voltage drop), wire-type EGCs must be increased proportionally in circular mil area per 250.122(D). This tool does not apply that adjustment.
Sections used
These are the sections the calculator applies. Look them up in your code book before you rely on the result, and check the code your AHJ has adopted.
Questions electricians ask
What does a ground wire size calculator figure out under NEC 2026?
It sets the minimum equipment grounding conductor from the rating of the breaker or fuse protecting the circuit, copper or aluminum, and shows the row of Table 250.122 it used. It does not size the grounding electrode conductor, which comes from Table 250.66.
Is there a ground wire size chart in the NEC?
Yes. Table 250.122 is the chart for the equipment grounding conductor. Find the breaker or fuse rating in the left column and read across to the copper or aluminum size. If your rating falls between rows, use the next row up.
What is the difference between a ground conductor size and a ground wire size?
They mean the same thing when you are sizing the wire that runs with a circuit: the equipment grounding conductor, from Table 250.122. The wire from the service to the ground rod or water pipe is a different conductor, the grounding electrode conductor, from Table 250.66.
What size ground wire do I need for a 200 A feeder?
Enter 200 in the calculator. Table 250.122 gives 6 AWG copper or 4 AWG aluminum for a 200 A overcurrent device. That is for the equipment grounding conductor, not the service grounding electrode conductor.
What size ground wire for a 100 A subpanel?
Enter 100. For a 100 A overcurrent device, Table 250.122 gives 8 AWG copper or 6 AWG aluminum.
Do I size the ground from the wire or the breaker?
From the breaker or fuse protecting the circuit. That is how Table 250.122 is arranged.
Does the ground have to be upsized for voltage drop?
A wire-type EGC does. Under 250.122(D), if the hot conductors are increased in size for anything other than derating, the EGC goes up in proportion.
Teach it in one class
Free slides, quiz, and instructor note: Grounding vs. bonding (NEC 2026 Article 250).
How this calculator was built
The calculator runs the same code as the Ask Shorty iPhone app. Automated tests check it against hand-worked answers, and every section it names is checked against the 2026 NEC text. It shows section numbers, not code text. Read the sections in your own code book and confirm which edition your AHJ enforces.
How we test the calculators. See something wrong? Tell us and we will check it against the code.
Related calculators
- Grounding electrode conductorGEC size from the service conductors, with ground rod and Ufer limits.
- Voltage dropVolts lost and percent drop on a copper or aluminum run, single- or three-phase.
- Box fillMinimum box volume from conductors, devices, clamps, and grounds.
Have a code question the calculator doesn’t cover?
Ask Shorty in plain English. You get a straight answer with the NEC 2026 section it came from.