What is an electrical ground and what does it do?
Electrical current always flows in a complete circle (circuit) and returns to its source. The current wants to flow through a path with least resistance. Normally, current flows from the hot (black) wire attached to a circuit breaker in the electrical panel through a plugged in device and returns through the neutral (white) wire.
The roundish third hole on an outlet is a ground, as is the round prong on a plug. A ground wire has very little resistance to current flow. The ground wire is connected to anything a person may touch, such as the body of a refrigerator or microwave oven. If either the hot or neutral wire shorts out to anything connected to the ground wire, a large current flow results, tripping the circuit breaker. Normally, the ground wire is never used except in case of a rare ground fault (short circuit) where current leaves its normal circuit.
The Earth forms an ultimate ground. It can absorb or dissipate an unlimited amount of electrical charge. The bare or green ground wire in each outlet is routed to the electric panel where it is connected to the neutral wire metal bar. This bar itself is connected to a metal pipe inside the house or a metal rod buried in the Earth outside of the house. This grounding circuit handles ground faults inside the house.
Outside the house on the utility pole, another ground wire travels from the transformer neutral wire down the pole into the Earth below. This grounding circuit dissipates buildup of electrical charges such as from lightning strikes.