What should be the size of the bonding jumper to the metal water piping system(s) based on?

The size of the bonding jumper to the metal water piping system is primarily determined by the size of the feeder or branch circuit supplying the building. This guideline is essential because the bonding jumper needs to be adequate enough to safely conduct any fault current that might occur.

When a fault occurs, a proper bonding jumper ensures that the electrical systems remain safe by providing a low-resistance path back to the panel, thus enabling circuit protection devices, such as breakers or fuses, to operate correctly and trip during a fault. The bonding jumper must therefore be sized appropriately according to the largest feeder or branch circuit that feeds electrical equipment in the building.

This approach helps in maintaining a safe grounding system, which is critical for preventing electrical shock hazards and allows for the protection of equipment by ensuring that all parts of the system are properly connected together.

In summary, the feeder or branch circuit size is directly related to the electrical load and fault currents, making it the relevant factor in determining the size of the bonding jumper appropriate for a given installation.