Electrical Grounding and Bonding

Electrical Grounding and Bonding

These two terms often get mixed up or can be confusing to many people especially apprentices.

The concept is quite simple though. Generally most systems use a grounded neutral. This means that in a two wire system with black as the hot wire and white as the neutral wire, current flows first through the black wire to the load (toaster, fridge, etc) then through the white back to the service panel where the white wires are all connected to the physical earth (ground). So if you measured the voltage compared to ground on the terminal where the white wire is attached to the load it would read zero or very close to zero. This means this side is grounded.

ground symbol

Bonding means you take every metallic object that runs on eletriciy and electrically tie it to the ground point in your service panel. In a two system (black and white) there is always a bare wire which people often call the ground wire. It is always securely attached the ground terminal in service panel but it is really designed to be your bonding wire. If you use metallic receptacle boxes the box itself is where this wire is attached. The metal parts of your toaster, freezer, dryer, stove, and so on are attached to this wire. This means no dangerous voltage can build up on the case due to a short from the power wire (black) to the case or through any other means. You are simply tying all these points physically to ground (the earth).

The difference between ground and bond is that one is meant to carry current (white neutral) as a normal part of its job and the other will only carry it if there has been a failure in the system. The bond wire will carry current only momentarily because the circuit breaker will trip as soon as it senses the failure through over current.