Ground Wire Sizing Calculator

Size equipment grounding conductors per NEC 250.122 based on overcurrent protection device rating.

Results

Visualization

How It Works

Equipment grounding conductors (EGC) provide a safe fault-current path back to the source, enabling breakers to trip quickly during ground faults. NEC 250.122 specifies minimum EGC sizes based on the overcurrent device rating.

The Formula

EGC size is a direct lookup from NEC Table 250.122 based on the rating of the overcurrent protection device (breaker or fuse) ahead of the circuit.

Variables

  • EGC — Equipment Grounding Conductor - protects against ground faults in branch circuits
  • GEC — Grounding Electrode Conductor - connects the grounding system to earth ground
  • OCPD — Overcurrent Protection Device (breaker or fuse) rating in amperes

Example

A circuit with a 20A breaker using copper wire needs a #12 AWG equipment grounding conductor per NEC 250.122. If using aluminum, the EGC must be #10 AWG.

Tips

  • The EGC must never be smaller than what NEC 250.122 requires, but can always be larger.
  • Aluminum grounding conductors must be one size larger than copper equivalents.
  • Equipment grounding conductors can be bare, covered, or insulated (green or green/yellow).
  • In metal conduit systems, the raceway itself can serve as the equipment grounding conductor.
  • Grounding and bonding are different concepts: grounding connects to earth, bonding connects metal parts together.