NEC 2002: Table 250.66
| Grounding Electrode Conductor for AC systems | |||
| Size of Largest Ungrounded Service Entrance Conductor* (AWG/kcmil) | Size of Grounding Electrode Conductor (AWG/kcmil) | ||
| Copper | Aluminum | Copper | Aluminum |
| 2 or smaller | 1/0 or smaller | 8 | 6 |
| 1 or 1/0 | 2/0 or 3/0 | 6 | 4 |
| 2/0 or 3/0 | 4/0 or 250 | 4 | 2 |
|
Over 3/0 through 350 |
Over
250 through 500 |
2 | 1/0 |
|
Over 350 through 600 |
Over
500 through 900 |
1/0 | 3/0 |
|
Over 600 through 1100 |
Over
900 through 1750 |
2/0 | 4/0 |
| Over 1100 | Over 1750 | 3/0 | 250 |
| *or Equivalent Area for Parallel Conductors | |||
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