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Find the minimum equipment grounding conductor size from the overcurrent device rating using NEC Table 250.122, for copper or aluminum.
Ask questions about your calculation results
3 free questions per session
AI provides general information, not financial advice. Always consult a qualified professional.
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.
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.
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.
NEC Table 250.122 requires 8 AWG copper or 6 AWG aluminum for a 100 amp overcurrent device.
For a 200 amp overcurrent device the equipment grounding conductor is 6 AWG copper or 4 AWG aluminum per Table 250.122.
By the overcurrent device rating. The equipment grounding conductor in Table 250.122 is based on the breaker or fuse, not the connected load.
Yes. Under NEC 250.122(B), if the phase conductors are increased in size, the equipment grounding conductor must be increased proportionally.
No. This is the equipment grounding conductor from Table 250.122. The grounding electrode conductor that goes to ground rods uses Table 250.66.