In a single nonmetallic raceway that contains conductors for circuits rated at 40, 60, and 100 amperes, how large should the aluminum equipment grounding conductor be?

The correct choice is based on the required size of the equipment grounding conductor (EGC) for the specifications provided in the question. The National Electrical Code (NEC) provides guidelines for determining the appropriate size of grounding conductors, particularly when multiple circuit ratings are involved.

When conductors are present from multiple circuits rated at different amperages, the size of the grounding conductor must be determined by the largest circuit that it serves. According to NEC Table 250.122, the minimum size of the EGC for circuits up to 100 amperes is often specified based on the largest overcurrent protection present in the raceway.

In this instance, the largest circuit is rated at 100 amperes. Consulting the NEC guidelines, a base size for an aluminum grounding conductor for a 100 ampere circuit is typically designated as 8 AWG. However, for conductors in a raceway with multiple circuits and the potential for increased fault current, the size may need to increase to adequately ensure safety and conductivity.

In practical applications, using a 6 AWG aluminum grounding conductor for larger systems or those with multiple circuits can provide additional safety margins against unanticipated fault conditions. This makes the aluminum equipment grounding conductor size 6 AWG appropriate for