What is the smallest size wire permitted to be used as a system bonding jumper in an 800-A fused safety switch fed from a transformer with four parallel sets of 3/0 AWG wire?

To determine the smallest size wire permitted to be used as a system bonding jumper in this scenario, it is essential to refer to the relevant code requirements. The National Electrical Code (NEC) provides guidelines for bonding jumpers based on the size of the conductors feeding a device and the overall rating of the equipment.

In this case, you have an 800-A fused safety switch fed from a transformer using four parallel sets of 3/0 AWG wire. The NEC specifies that the bonding jumper must be sized appropriately to ensure safety and adequate fault current handling.

The total ampacity of the conductors should be calculated by taking into account the number of conductors in parallel; however, for bonding jumper sizing, the key point is the rating of the protective device, which is 800 A. The NEC refers specifically to Table 250.102(C) for bonding jumper sizes relative to the largest ungrounded conductor.

According to this table, for a 800-A service, the minimum size bonding jumper is typically 2/0 AWG copper or 2/0 AWG aluminum. The correct answer being 2/0 AWG indicates that this is the smallest allowable size for the bonding jumper to ensure effective grounding and safety.

Understanding