NEC 250.66 Grounding Electrode Conductor Sizing
The Grounding Electrode Calculator determines GEC size based on NEC Table 250.66. Input service conductor size and electrode type for instant AWG/kcmil.
NEC 250.66 Table (Copper)
| Service Size (kcmil) | ≤ 2/0 | 3/0 – 350 | 400 – 600 | 750 – 1200 | > 1200 |
|---|---|---|---|---|---|
| Rod/Pipe/Plate | #8 | #6 | #4 | #2 | #1/0 |
| Ground Ring | #2 Cu (20 ft min) | ||||
| Concrete-Encased | #4 Cu (20 ft min) | ||||
| Water Pipe | Same as service | ||||
Key Rules (NEC 250.66)
- Rod/Plate/Pipe: Max #4 Cu or #2 Al
- Ground Ring: #2 Cu minimum
- Ufer: #4 Cu minimum
- Water Pipe: Full size of service conductor
- Aluminum GEC: Not in contact with earth
Examples
- 200A service, 2/0 Cu → Rod → #8 Cu GEC
- 400A service, 500 kcmil Cu → Rod → #2 Cu GEC
- Any size → Ground Ring → #2 Cu GEC
Common Mistakes
- Using equipment grounding size for GEC
- Undersizing for large services
- Using Al GEC in soil
- Forgetting supplemental electrode
Best Practices
- Always bond metal water pipes
- Use exothermic weld for buried connections
- Label GEC at panel
- Verify with Ground Resistance
Conclusion
Proper GEC sizing ensures safety and code compliance. Use with Breaker Size and Conduit Fill. Build safely with 1000 Calculators.