What is the minimum size equipment grounding conductor required for a 100 ampere underground dwelling feeder with conductors increased in size from 3 AWG copper to 1 AWG copper?

For a 100 ampere underground dwelling feeder, the minimum size for the equipment grounding conductor is determined based on the size of the ungrounded conductors in the feeder. When the ungrounded conductors are increased in size from 3 AWG copper to 1 AWG copper, the requirements for the grounding conductor also change accordingly.

According to the National Electrical Code (NEC), the size of the equipment grounding conductor depends on the ampacity of the conductors supplying the load. When the conductors are sized at 1 AWG copper, the NEC specifies that the minimum size equipment grounding conductor must be 4 AWG copper. This ensures that the grounding system is sufficiently robust to handle fault currents and provide effective grounding for safety in the electrical system.

The correct answer reflects this standard, ensuring compliance with safety regulations and the protection of both people and equipment.