What is the minimum size of the bonding jumper for a 400-amp, 480-volt delta service with 600 kcmil SE conductors?

The correct answer of 1/0 for the minimum size of the bonding jumper is based on the National Electrical Code (NEC) requirements, which stipulate that bonding jumpers must be sized according to the size of the service conductors. In this case, with 600 kcmil conductors being used for a 400-amp, 480-volt delta service, you reference Table 250.102(C)(1) in the NEC, which outlines the requirements for bonding jumpers.

For conductors that are 250 kcmil or larger, the bonding jumper must be at least as large as the largest ungrounded conductor if the ungrounded conductors are between 250 kcmil and 600 kcmil. This effectively requires a bonding jumper size of 1/0 AWG for the given service size.

In contrast, other options like 2/0, 3, and 3/0 do not meet the specific minimum requirement of the NEC for the bonding jumpers based on the size of the service conductors in this scenario. They either exceed the requirements or do not correspond accurately to the given 400-amp service. Understanding these sizing requirements is crucial for ensuring both safety and compliance