Why is the ground sized from the breaker, not the load?

NEC Table 250.122 sizes the equipment grounding conductor from the rating of the overcurrent device protecting the circuit. The EGC must carry fault current long enough for that device to trip, so its size scales with the protection rather than the normal operating load.

What size ground does a 100 A breaker need?

Per Table 250.122 a circuit protected at 100 amps requires a minimum 8 AWG copper or 6 AWG aluminum equipment grounding conductor. Larger overcurrent ratings step the EGC up accordingly through the table.

How do parallel conductors change the ground size?

NEC 250.122(F) requires that when phase conductors are run in parallel in separate raceways, a full-size equipment grounding conductor sized to the OCPD must be installed in each raceway. You do not divide the ground among the raceways.

Do I upsize the ground if I upsize the conductors?

Yes. NEC 250.122(B) requires that if you increase the phase-conductor size for voltage drop, the equipment grounding conductor must be increased proportionally by the same cross-sectional area ratio so its fault-clearing capacity stays matched.

Can the ground ever be smaller than required by the table?

No, the table gives the minimum, but the EGC also never needs to be larger than the circuit conductors themselves. Use whichever is smaller of the table value and the phase conductor size when the phase conductors are unusually small for the protection.

Equipment Grounding Conductor Sizing (NEC 250.122)

The equipment grounding conductor is the safety path that carries fault current back to clear a breaker, and it is sized from the overcurrent device, not the load. This tool reads the minimum size straight from NEC Table 250.122 for copper or aluminum.

How it works

The lookup keys on the overcurrent protective device (OCPD) rating and returns the minimum conductor for the chosen material:

find the first table row where OCPD ≤ row maximum
EGC = copper or aluminum size in that row
if parallel sets > 1 → run that full EGC in EVERY raceway (250.122(F))

For example a 60 A circuit needs 10 AWG copper, a 200 A circuit needs 6 AWG copper, and a 400 A circuit needs 3 AWG copper.

Example and notes

A feeder protected at 200 A takes a minimum 6 AWG copper or 4 AWG aluminum grounding conductor. If that feeder is run as two parallel sets in separate conduits, each conduit must contain its own full 6 AWG copper EGC, not a half-size conductor. Remember the proportional-upsize rule in 250.122(B): increasing the phase conductors for voltage drop forces a matching increase in the grounding conductor by the same area ratio, so recompute it whenever you upsize the circuit.