NEC 250.122 — Sizing the Equipment Grounding Conductor (EGC) by Breaker Amperage

NEC 250.122 sizes the equipment grounding conductor (EGC) — the green or bare wire that bonds metal equipment chassis back to the service. Different rule and different table from the grounding electrode conductor (GEC) sized by 250.66.

The Table 250.122 sizing matrix (most common values):

• 15 A breaker: 14 AWG copper EGC (12 AWG aluminum)
• 20 A breaker: 12 AWG copper EGC (10 AWG aluminum)
• 30-60 A breaker: 10 AWG copper EGC
• 100 A breaker: 8 AWG copper EGC
• 200 A breaker (typical residential sub-panel): 6 AWG copper EGC
• 400 A breaker: 3 AWG copper EGC

Common applications:

Sub-panel feeders — when you run a feeder from the main panel to a sub-panel, the EGC sizes per Table 250.122 to the breaker protecting that feeder. A 100 A sub-panel feed needs a #8 CU EGC. A 200 A sub-panel needs a #6 CU EGC.

EV charger circuits — a 60 A EV charger circuit needs a #10 CU EGC (per Table 250.122 for breakers up to 60 A). The branch run is typically (2) #6 CU phase conductors + (1) #10 CU EGC.

EGC upsizing per 250.122(B): when phase conductors are upsized for voltage drop, the EGC must be upsized PROPORTIONALLY. If you upsize from #6 CU to #4 CU on the phases (because the run is long), the EGC increases too. This is the rule most contractors miss on long EV charger runs.

Difference from GEC: the GEC (sized by 250.66) bonds the service to the grounding electrode SYSTEM (ground rod, water main). The EGC (sized by 250.122) bonds equipment chassis BACK to the service. They serve different roles.

For voltage drop checks on long EGC-sensitive runs, use the free Malfettone Voltage Drop Calculator at /tools/voltage-drop. For grounding overall, see our guide on NEC 250.