Ground Wire Size Calculator — NEC Table 250.122

Find the minimum equipment grounding conductor (EGC) size for any circuit. Enter the overcurrent protective device (OCPD) rating and select copper or aluminum. This ground wire size calculator looks up NEC Table 250.122 — the required reference for sizing EGCs on branch circuits, feeders, and service entrance installations.

Circuit Details

Rating of the breaker or fuse protecting this circuit.

Results

Minimum EGC Size —
NEC Table 250.122 Row —

Minimum EGC per NEC Table 250.122. If conductors are upsized for voltage drop, EGC must also increase per NEC 250.122(B). Verify against current code and local amendments.

Worked Example — 60A HVAC Circuit Equipment Ground
1Given: 60A 2-pole breaker protecting an HVAC condenser unit. What is the minimum equipment grounding conductor (EGC) size?
2Look up NEC Table 250.122: For a 60A overcurrent device, the minimum copper EGC = #10 AWG.
3Aluminum EGC option: NEC 250.122 Note 1 — if using aluminum, #8 AWG aluminum is the minimum (one size larger than copper minimum).
4Upsizing note: If the phase conductors are upsized for voltage drop, the EGC must be proportionally upsized per NEC 250.122(B).
✅ 60A HVAC circuit: minimum copper EGC = #10 AWG per NEC Table 250.122. Use #8 AWG aluminum if running aluminum EGC.

Also try:

circuit breaker size calculator — NEC 240.6 AWG wire size calculator for ampacity & voltage drop feeder wire size calculator — 100A/200A service NEC ampacity chart — Table 310.15(B)(16) reference electric dryer wire size guide — 30A circuit

How to Use This Ground Wire Size Calculator

Select the rating of the overcurrent protective device (OCPD) protecting the circuit, and choose copper or aluminum for the EGC material. The calculator looks up the NEC Table 250.122 row for that OCPD rating and returns the minimum required AWG. This is the absolute minimum — if phase conductors are upsized for voltage drop, increase the EGC proportionally per NEC 250.122(B).

Why Ground Wire Size Matters

An undersized EGC may not carry enough fault current to clear the overcurrent device quickly, leaving equipment energized at a dangerous voltage. The NEC Table 250.122 minimums ensure the EGC can handle the worst-case fault current for the associated OCPD.

EGC sizing is frequently underspecified on subpanel feeders and service entrances — where the phase conductors get attention but the grounding means does not.

What Affects EGC Size

The OCPD rating is the primary driver. Conductor material matters because aluminum has higher resistance, requiring a larger AWG for equivalent fault-current capacity. If phase conductors are upsized beyond the NEC table minimum (for voltage drop, derating, or other reasons), the EGC must also be increased proportionally per NEC 250.122(B).

Common Ground Wire Sizing Scenarios

  • Sizing the EGC for a 20-amp kitchen or bathroom circuit (#12 AWG copper minimum)
  • Finding the EGC for a 100-amp subpanel feeder (#8 AWG copper minimum)
  • Sizing an aluminum EGC for a 200-amp service entrance (#4/0 AWG aluminum)
  • Checking whether an existing EGC must increase after upsizing circuit conductors for voltage drop
  • Finding the correct ground wire gauge for a 60-amp EV charger or HVAC circuit

Frequently Asked Questions

NEC Table 250.122 determines the minimum EGC size based on the overcurrent device protecting the circuit, for both copper and aluminum conductors.

An EGC connects the metal parts of equipment not normally carrying current back to the grounding system, providing a fault current return path so overcurrent devices can clear ground faults quickly.

Per NEC Table 250.122, a 20-amp OCPD requires a minimum #12 AWG copper or #10 AWG aluminum EGC.

Per NEC Table 250.122, a 100-amp overcurrent device requires a minimum #8 AWG copper or #6 AWG aluminum equipment grounding conductor.

Aluminum EGCs are permitted by NEC 250.122 but must be larger than copper equivalents. Aluminum cannot contact earth or concrete, and terminations must be rated for aluminum conductor use.

Yes. Per NEC 250.122(B), when circuit conductors are increased in size beyond the NEC table minimum, the EGC must be proportionally increased using the ratio of the new conductor circular mil area to the original table-minimum area.