What is the smallest size wire permitted for a main bonding jumper in a panel with a 175-A main breaker, when the service entrance conductors are 2/0 AWG?

For a service entrance with conductors of 2/0 AWG, the size of the main bonding jumper must be sufficient to ensure safety and reliability in electrical installations. According to the National Electrical Code (NEC) guidelines, the size of the main bonding jumper is based on the size of the service-entrance conductors.

In this case, for 2/0 AWG conductors, the code specifies that the minimum size for the bonding jumper, particularly when considering a panel with a 175-A ampacity, should be no less than 4 AWG copper or 2 AWG aluminum. This requirement ensures that the bonding jumper can carry the maximum ground fault current until protective devices operate.

Therefore, a wire size of 4 AWG is appropriate and meets the code requirements for a main bonding jumper in this scenario, ensuring proper grounding and safety for the electrical system.