The main purpose of this bond is to ensure that the metal water pipe is at the same zero voltage to ground as the service grounded conductor. A secondary purpose is to ensure that there is a path back to the service for electrical current flow if the metal water pipe becomes energized.

What is the purpose of bonding?

Bonding is used to reduce the risk of electric shocks to anyone who may touch two separate metal parts when there is a fault somewhere in the supply of electrical installation. By connecting bonding conductors between particular parts, it reduces the voltage there might have been.

Do water pipes need to be bonded?

Since Section 250.104(A) requires all water-piping systems to be bonded back to the service, and hot or cold water lines are not specifically mentioned, both hot and cold water lines must be bonded and connected back to the building service.