Equipment Grounding Conductors
Minimum EGC sizes based on overcurrent protection rating. Includes proportional increase rules.
Professional Usage Disclaimer
This data is provided for informational purposes only. Always verify with the latest edition of the National Electrical Code (NFPA 70) and consult with a licensed electrical professional or AHJ (Authority Having Jurisdiction) before performing any electrical work. Zing² is a reference tool, not a substitute for qualified engineering.
Professional Field Notes & Gotchas
- ▸The 250.122(B) Rule: If ungrounded conductors are increased in size for reasons other than ampacity (like voltage drop), the EGC MUST be increased proportionately.
- ▸Inspection Trap: AHJs often fail jobs where a 4/0 Aluminum set is upsized to 300 kcmil for distance, but the ground stays at #4. Always recalculate your ground size during voltage drop runs.
- ▸Termination: Verify that your EGC is rated for the terminal temperature (usually 75°C) to prevent overheating at the lug under fault conditions.
- ▸Parallel Runs: When installers run parallel sets, each raceway must contain an EGC sized based on the overcurrent protective device.
NEC 2023 vs 2026: What changed?
NEC 2023 vs 2026: No changes were made to the core amperage-to-size values. However, language was clarified regarding 'proportional increase' to ensure consistent math when upsizing for voltage drop across all jurisdictions.
Technical FAQs
What size ground for a 100A subpanel?
Per NEC Table 250.122, a 100A overcurrent protection device (OCPD) requires a #8 Copper or #6 Aluminum equipment grounding conductor.
Does the ground size change if I use Aluminum wire?
Yes. Due to higher resistance, Aluminum requires a larger cross-section. For a 200A circuit, you would need a #6 Copper or a #4 Aluminum EGC.
Can I use the conduit as a ground instead of a wire?
Per NEC 250.118, certain metal raceways like EMT and RMC are recognized as EGCs. However, many engineers and AHJs require a redundant green pull-wire for increased safety and reliability.