NEC 250.66 grounding electrode conductor sizing
The NEC Table 250.66 grounding electrode conductor (GEC) sizes, plus the 250.66(A)–(C) caps that apply when the GEC's only connection is to a rod, a concrete-encased electrode (Ufer) or a ground ring.
Table 250.66 — GEC by service-entrance conductor (copper)
| Largest service/derived conductor (Cu) | Copper GEC |
|---|---|
| 2 AWG or smaller | 8 AWG |
| 1 or 1/0 AWG | 6 AWG |
| 2/0 or 3/0 AWG | 4 AWG |
| Over 3/0 through 350 kcmil | 2 AWG |
| Over 350 through 600 kcmil | 1/0 AWG |
| Over 600 through 1100 kcmil | 2/0 AWG |
| Over 1100 kcmil | 3/0 AWG |
Electrode-specific caps
- 250.66(A) — where the GEC's sole connection is to a ground rod/pipe/plate, it need not be larger than 6 AWG copper.
- 250.66(B) — where the sole connection is to a concrete-encased electrode (Ufer), it need not be larger than 4 AWG copper.
- 250.66(C) — where the sole connection is to a ground ring, it need not be larger than the ring conductor (min 2 AWG).
These caps are why a typical residential PV/service GEC to a driven ground rod is 6 AWG copper even on a large service. Solar Scripto applies the rod/Ufer caps automatically.
Related: 250.122 EGC.
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