A 400-amp service requires bonding bushings due to wallowed out holes. What is the minimum size of bonding jumpers needed from the ground bar to these bushings?

For a 400-amp service, when bonding bushings are used due to issues such as wallowed out holes, it is essential to establish a reliable bonding connection to ensure that any fault currents can safely return to the ground. According to the NEC (National Electrical Code) requirements and guidelines for bonding conductors, the minimum size of bonding jumpers is determined by the size of the service.

In this case, for a 400-amp service, the minimum size of the bonding jumper from the ground bar to the bonding bushings is required to be at least a size 2 AWG copper conductor, which is equivalent to a larger size in aluminum. This requirement ensures that the bonding jumper can handle the potential fault currents effectively, providing a safe path for electricity without overloading or causing potential fire hazards.

While larger sizes like 1/0 or 3/0 may be used in different situations or specific installations, for this specific context of a 400-amp service, a size 2 AWG is the minimum acceptable to maintain compliance with safety standards set forth by the NEC regarding bonding jumpers.