Why is there 3 wires in plugs and lights?

Question

okay i have installed a couple lightyings, plugs, and my sound system, but i still dont understand. in a car, the power(live) wire goes to the positive or whatever side of the device. then the ground goes well to something it can be grounded on. thats a loop, so why is it in plugs in a house that they have a power ground and another wire. whats its purpose because if a amp in a car can run without one, why cant these. explain it to me

Answer 1

Houses have power and (essentially) two grounds.

The neutral AND ground wires are the same potential.

Answer 2

The neutral and ground wires in a house actually go to the exact same place.  The difference is that the ground wire is hooked up directly to the metal casing of the appliance while the neutral wire is what is used to complete the electrical circuit.  If a live wire within the appliance were to become loose and short against the metal casing of the appliance then the ground wire connected to it will cause the fuse/breaker to trip so that the affected appliance wouldn't receive anymore power rather than having somebody receive a fatal shock just by touching the appliance.  It is possible to hook up a three prong plug to a two prong outlet using a cheater plug or cutting off the ground prong and the device will work fine, but then you would be removing the safety feature which could lead to death if the live wire shorted to the appliance.

Answer 3

A house runs on AC which has Live, neutral and ground. In some 110V systems neutral and ground are not the same thing as the supply is 55V-0-55V.