What Size Ground Wire for a 250 Amp Service or Breaker?
Verified against NEC 2023, checked against the 2026 edition · Last checked August 18, 2026
A 250 amp breaker or feeder needs an equipment grounding conductor of 4 AWG copper or 2 AWG aluminum · Table 250.122. A 250 amp dwelling service is sized differently: its grounding electrode conductor comes from Table 250.66 based on the service conductor size. A rod-only electrode caps it at 6 AWG copper · 250.66(A). Both answers are below.
Common on this rating: commercial feeders and services. Run with 250 kcmil copper circuit conductors, the ground is 4 AWG copper.
Two different tables answer this question. A breaker, circuit or sub panel takes an equipment grounding conductor from Table 250.122, entered with the breaker rating. A service takes a grounding electrode conductor from Table 250.66, entered with the service conductor size. Mixing them up can change the answer by a size or more.
| Conductor | Size | Basis |
|---|---|---|
| Copper EGC | 4 AWG | Table 250.122 |
| Aluminum EGC | 2 AWG | Table 250.122 |
The EGC never needs to be larger than the circuit conductors · 250.122(A). Upsized circuit conductors mean a proportionally upsized EGC · 250.122(B). Parallel runs in separate raceways carry a full-size EGC in each raceway · 250.122(F).
| Service conductors | GEC | Basis |
|---|---|---|
| Copper service, 4/0 AWG | 2 AWG Cu or 1/0 AWG Al | Table 250.66 |
| Aluminum service, 300 kcmil | 2 AWG Cu or 1/0 AWG Al | Table 250.66 |
| Rod, pipe or plate electrode only | 6 AWG Cu or 4 AWG Al | 250.66(A) cap |
Service conductor sizes per the 83% rule of 310.12. The rod cap applies when the conductor serves only rod, pipe or plate electrodes; a concrete-encased electrode caps at 4 AWG copper · 250.66(B). Outdoors, aluminum GEC terminations stay 18 inches off the earth · 250.64(A).
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Common questions
- What size ground wire for a 250 amp breaker?
- An equipment grounding conductor of 4 AWG copper or 2 AWG aluminum, from Table 250.122. The EGC never needs to be larger than the circuit conductors · 250.122(A).
- What size ground wire for a 250 amp sub panel?
- The same as the breaker answer: 4 AWG copper or 2 AWG aluminum, sized by the 250 A feeder breaker per Table 250.122.
- What size ground wire for a 250 amp service?
- That is the grounding electrode conductor. For a 250 A one-family dwelling with 4/0 AWG copper service conductors: 2 AWG copper or 1/0 AWG aluminum · Table 250.66. With 300 kcmil aluminum service conductors the row is the same: 2 AWG copper.
- Why is the ground to my rod smaller than the table says?
- A grounding electrode conductor that runs only to rod, pipe or plate electrodes never needs to be larger than 6 AWG copper or 4 AWG aluminum · 250.66(A). Concrete-encased electrodes cap at 4 AWG copper · 250.66(B).
- Is the ground wire the same as the neutral?
- No. The grounded service conductor, the neutral, is a current-carrying conductor sized by 250.24(C) and 220.61. It is not the EGC of Table 250.122 and not the GEC of Table 250.66.
- What if my circuit conductors were upsized for voltage drop?
- If the circuit conductors were upsized for voltage drop, the EGC must be upsized in the same ratio of circular-mil area · 250.122(B).