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Grounding Calculator
NEC 250 grounding electrode conductor sizing with electrode type requirements
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Service & Grounding Parameters
NEC 250.66 — Grounding Electrode Conductor Size
Required GEC Size (Copper)
2 AWG
For service entrance conductor: 4/0 AWG
Ground Rod(s) — Requirements
- •Minimum 8 ft driven depth (NEC 250.53(G))
- •Minimum 5/8" diameter for iron/steel, 1/2" for copper-clad
- •If single rod exceeds 25 ohms, a second rod is required (NEC 250.53(A)(2))
- •Second rod must be spaced ≥ 6 ft from first (NEC 250.53(A)(3))
- •GEC to ground rod(s) need not be larger than 6 AWG copper
⚠ If single ground rod resistance exceeds 25 ohms, a second rod is required spaced ≥ 6 ft apart
NEC Table 250.66 — Full Reference
| Service Conductor | GEC (Cu) | GEC (Al) |
|---|---|---|
| 2 AWG or smaller | 8 AWG | 6 AWG |
| 1 AWG or 1/0 AWG | 6 AWG | 4 AWG |
| 2/0 or 3/0 AWG | 4 AWG | 2 AWG |
| Over 3/0 through 350 kcmil | 2 AWG | 1/0 AWG |
| Over 350 through 600 kcmil | 1/0 AWG | 3/0 AWG |
| Over 600 through 1100 kcmil | 2/0 AWG | 4/0 AWG |
| Over 1100 kcmil | 3/0 AWG | 250 kcmil |
250.64(A)GEC shall be copper, aluminum, or copper-clad aluminum; solid or stranded; insulated, covered, or bare
250.64(B)GEC shall be installed in one continuous length without splice (except irreversible compression or exothermic)
250.66GEC sizing per Table 250.66 based on largest service-entrance conductor
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