Size the equipment grounding conductor.
Enter the breaker or fuse rating and the conductor material to get the minimum equipment grounding conductor size from NEC Table 250.122, for copper or aluminum.
Your circuit
What this means
Ground size by breaker rating
| Breaker / fuse rating | Copper EGC | Aluminum EGC |
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How ground sizing works
Sizing the Equipment Grounding Conductor
The equipment grounding conductor is sized from the rating of the overcurrent device that protects the circuit, not from the circuit load. NEC Table 250.122 gives the minimum size for each breaker or fuse rating. This calculator returns that minimum for copper or aluminum.
For a 100 amp breaker, for example, the table requires 8 AWG copper or 6 AWG aluminum.
When the Ground Must Be Upsized
If the circuit conductors are made larger than required, for instance to control voltage drop on a long run, NEC 250.122(B) requires the equipment grounding conductor to be increased in proportion to the circular mil increase of the ungrounded conductors. The table value is the starting point, not always the final size.
Grounding Conductor vs Grounded Conductor
The equipment grounding conductor in Table 250.122 is the bonding path that clears faults. It is different from the grounded conductor, which is the neutral, and from the grounding electrode conductor that connects to ground rods and is covered by Table 250.66.
Common questions
What size ground for a 100 amp breaker?
NEC Table 250.122 requires 8 AWG copper or 6 AWG aluminum for a 100 amp overcurrent device.
What size ground for a 200 amp service?
For a 200 amp overcurrent device the equipment grounding conductor is 6 AWG copper or 4 AWG aluminum per Table 250.122.
Is the ground sized by load or by breaker?
By the overcurrent device rating. The equipment grounding conductor in Table 250.122 is based on the breaker or fuse, not the connected load.
Do I upsize the ground if I upsize the wires?
Yes. Under NEC 250.122(B), if the phase conductors are increased in size, the equipment grounding conductor must be increased proportionally.
Does this give the grounding electrode conductor size?
No. This is the equipment grounding conductor from Table 250.122. The grounding electrode conductor that goes to ground rods uses Table 250.66.
Minimum sizes from NEC Table 250.122 for reference only. Always verify against the current adopted code and your inspector. Upsizing for voltage drop may require a larger equipment grounding conductor under 250.122(B).