What is ground circuit?

The part of the circuit that is tied to a ground rod that is usually 6-8 ft long and is driven in the actual ground outside a building. Most local electrical codes require the ground circuit also be tied to the neutral bar in the electrical service panel. Effectively, you are causing the neutral bar to be grounded electrically to physical earth ground.

A ground circuit can also be on a vehicle. It usually is the car body and chassis used as a return path for electrical currents back to the battery negative post. Some vehicles use a positive ground instead of a negative ground (European vehicles usually).