Minimum sizing of an equipment grounding conductor terminal/conductor is determined based on the maximum ampere rating of the overcurrent protection for the field-wiring conductor supplying the panel — with the exception of equipment grounding terminal for grounding conductors are not required to retain a wire larger than the field wiring conductors supplying the panel.
Maximum Ampere Rating of Overcurrent Protection | Copper AWG | Aluminum AWG |
15 | 14 | 12 |
20 | 12 | 10 |
30 | 10 | 8 |
40 | 10 | 8 |
60 | 10 | 8 |
100 | 8 | 6 |
200 | 6 | 4 |
300 | 4 | 2 |
400 | 3 | 1 |
This table was reproduced, in-part, from UL508A documentation.