The sprinkler piping needs to be bonded so that the electrical potential between any electrical source and the sprinkler piping will be the same thus limiting the electrical shock potential that could be received from differential electrical voltage fields. I.e. a light fixture MC cable chaffs, and allows a hot conductor to touch the sprinkler piping...... A contractor goes up and grabs a sprinkler pipe somewhere else and establishes a ground when they touch the pipe, they receive the shock. Bonding of the sprinkler piping would allow an opportunity of the path back to ground to be done by the bonding wire instead of when a person grabs the sprinkler pipe elsewhere in the building.
Bonding is not grounding... it is tying metallic surfaces together so that they all have the same electrical potential..... This is a over simplified explanation of the reason you need to bond sprinkler piping. The sprinkler piping needs to be bonded so that the electrical potential between any electrical source and the sprinkler piping will be the same thus limiting the electrical shock potential that could be received from differential electrical voltage fields.
