Grounding Conductor Size Chart — NEC Tables 250.66 & 250.122
NEC grounding tables: grounding electrode conductor sizes per Table 250.66 and equipment grounding conductor sizes per Table 250.122.
Updated August 20, 2026
The NEC sizes the two grounding conductors in a premises system from two different variables, and mixing them up is the classic grounding mistake. The grounding electrode conductor (GEC) — the wire from the service neutral to the ground rods, water pipe, or footing steel — is sized from the largest ungrounded service-entrance conductor per Table 250.66, because it must be proportional to the service itself. The equipment grounding conductor (EGC) — the fault-return wire run with every branch circuit and feeder — is sized from the rating of the overcurrent device ahead of it per Table 250.122, because its only job is to carry enough fault current to trip that breaker or fuse fast.
Both tables are transcribed in full below. In Table 250.66, parallel service conductors count as their combined circular-mil area, and Section 250.66(A)–(C) caps the GEC where it runs to a made electrode: never larger than 6 AWG copper (4 AWG aluminum) to a rod, pipe, or plate, and never larger than 4 AWG copper to a concrete-encased electrode. In Table 250.122, the ampere column is a "not exceeding" band — a 50 A breaker falls in the 60 A row — and Section 250.122(B) requires the EGC to be upsized proportionately whenever the circuit conductors are upsized for voltage drop or any reason other than ampacity.
Grounding Electrode Conductor Sizes — NEC Table 250.66
| Largest ungrounded service conductor — copper | Largest ungrounded service conductor — aluminum / CCA | GEC — copper | GEC — aluminum / CCA |
|---|---|---|---|
| 2 AWG or smaller | 1/0 AWG or smaller | 8 AWG | 6 AWG |
| 1 or 1/0 AWG | 2/0 or 3/0 AWG | 6 AWG | 4 AWG |
| 2/0 or 3/0 AWG | 4/0 AWG or 250 kcmil | 4 AWG | 2 AWG |
| Over 3/0 AWG through 350 kcmil | Over 250 through 500 kcmil | 2 AWG | 1/0 AWG |
| Over 350 through 600 kcmil | Over 500 through 900 kcmil | 1/0 AWG | 3/0 AWG |
| Over 600 through 1100 kcmil | Over 900 through 1750 kcmil | 2/0 AWG | 4/0 AWG |
| Over 1100 kcmil | Over 1750 kcmil | 3/0 AWG | 250 kcmil |
Parallel service conductors count as the equivalent area (sum of circular mils); where there are no service-entrance conductors, size from the equivalent conductor required for the load served. Per 250.66(A)–(C), the GEC need not be larger than 6 AWG Cu / 4 AWG Al to a rod, pipe, or plate electrode, 4 AWG Cu to a concrete-encased electrode, or the ring conductor size to a ground ring. CCA = copper-clad aluminum.
Minimum Equipment Grounding Conductor Sizes — NEC Table 250.122
| OCPD rating, not exceeding (A) | Copper EGC | Aluminum / CCA EGC |
|---|---|---|
| 15 | 14 AWG | 12 AWG |
| 20 | 12 AWG | 10 AWG |
| 30 | 10 AWG | 8 AWG |
| 40 | 10 AWG | 8 AWG |
| 60 | 10 AWG | 8 AWG |
| 100 | 8 AWG | 6 AWG |
| 200 | 6 AWG | 4 AWG |
| 300 | 4 AWG | 2 AWG |
| 400 | 3 AWG | 1 AWG |
| 500 | 2 AWG | 1/0 AWG |
| 600 | 1 AWG | 2/0 AWG |
| 800 | 1/0 AWG | 3/0 AWG |
| 1000 | 2/0 AWG | 4/0 AWG |
| 1200 | 3/0 AWG | 250 kcmil |
| 1600 | 4/0 AWG | 350 kcmil |
| 2000 | 250 kcmil | 400 kcmil |
| 2500 | 350 kcmil | 600 kcmil |
| 3000 | 400 kcmil | 600 kcmil |
| 4000 | 500 kcmil | 750 kcmil |
| 5000 | 700 kcmil | 1200 kcmil |
| 6000 | 800 kcmil | 1200 kcmil |
The rating column is a ceiling: use the first row whose ampere value is not exceeded by the breaker or fuse (a 50 A breaker uses the 60 A row). Per 250.122(B), upsize the EGC proportionately (by circular-mil ratio) when the ungrounded conductors are upsized for reasons other than ampacity, such as voltage drop. The 4000 A aluminum cell was 800 kcmil in the 2008 NEC and is 750 kcmil in current editions.
Sources & Further Reading
- NEC (NFPA 70), Table 250.66 — Grounding Electrode Conductor for Alternating-Current Systems — digit-verified against the zing2.app NEC 2020/2023 table, the buildmyowncabin.com NEC 2014 reproduction, and the Tucson Electric Power / UniSource Energy SR-453 grounding standard (three independent reproductions, all seven rows identical)
- NEC (NFPA 70), Table 250.122 — Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment — digit-verified against the buildmyowncabin.com NEC 2014 reproduction and the zing2.app NEC 2023 table; TEP SR-453 used as the third check (agrees except the 4000 A aluminum cell, an adjudicated 2008→2011 edition revision from 800 to 750 kcmil)
- NEC 250.66(A)–(C) and 250.122(B) — made-electrode GEC caps and the proportional EGC upsizing rule, as summarized in the same reproductions
Frequently Asked Questions
What size grounding electrode conductor does a 200 A residential service need?
A typical 200 A service is wired with 2/0 AWG copper or 4/0 AWG aluminum service-entrance conductors — both land in the third row of Table 250.66, so the GEC is 4 AWG copper (or 2 AWG aluminum). If that GEC runs only to ground rods, 250.66(A) caps it at 6 AWG copper regardless; the 4 AWG requirement applies to the run to a water-pipe or concrete-encased electrode.
What is the difference between a GEC and an EGC?
The grounding electrode conductor connects the service to earth (rods, water pipe, footing steel) and is sized from the service conductors per Table 250.66. The equipment grounding conductor runs with the circuit conductors to bond metal enclosures, and is sized from the breaker or fuse rating per Table 250.122 — its job is to carry fault current back to the source so the OCPD trips, not to reach earth.
What size ground wire does a 50 A circuit need?
Table 250.122 has no 50 A row, and the ampere column reads "not exceeding" — so a 50 A breaker uses the 60 A row: 10 AWG copper or 8 AWG aluminum. The same logic applies at any in-between rating: a 90 A breaker uses the 100 A row (8 AWG copper), and a 175 A breaker uses the 200 A row (6 AWG copper).
Do I have to upsize the ground wire if I upsize the circuit for voltage drop?
Yes. NEC 250.122(B) requires the EGC to be increased in proportion to the circular-mil increase of the ungrounded conductors whenever they are upsized for any reason other than ampacity. If a 20 A circuit is run in 8 AWG instead of 12 AWG for a long voltage-drop run (2.53× the circular mils), the 12 AWG EGC from the table must grow by the same ratio — 16,510 cmil, which pushes it to 8 AWG as well.
Try the Calculators
Grounding Conductor Size Chart — NEC Tables 250.66 & 250.122 — reuven.tools/reference/grounding-conductor-sizes — verified against: NEC (NFPA 70), Table 250.66 — Grounding Electrode Conductor for Alternating-Current Systems — digit-verified against the zing2.app NEC 2020/2023 table, the buildmyowncabin.com NEC 2014 reproduction, and the Tucson Electric Power / UniSource Energy SR-453 grounding standard (three independent reproductions, all seven rows identical); NEC (NFPA 70), Table 250.122 — Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment — digit-verified against the buildmyowncabin.com NEC 2014 reproduction and the zing2.app NEC 2023 table; TEP SR-453 used as the third check (agrees except the 4000 A aluminum cell, an adjudicated 2008→2011 edition revision from 800 to 750 kcmil); NEC 250.66(A)–(C) and 250.122(B) — made-electrode GEC caps and the proportional EGC upsizing rule, as summarized in the same reproductions