In electrical engineering, ground or earth is the reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the earth.
Electrical circuits may be connected to ground (earth) for several reasons. In mains powered equipment, exposed metal parts are connected to ground so that if, due to any fault conditions, a “line” supply voltage connection occurs to any such conductive parts, the current flow will then be such that any protective equipment installed for either overload or “leakage” protection will operate and disconnect the line voltage. This is done to prevent harm resulting to the user from coming in contact with any such dangerous voltage in a situation where the user may, at the same time, also come in contact with an object at ground/earth potential. In electric power distribution systems, a protective earth (PE) conductor is an essential part of the safety provided by the earthing system.