Earthing provides a low impedance ground path for power if an insult fails and a live cable comes into contact with an exposed part of a device, causing the device to be live and potentially dangerous to use. Ground is also used to provide a neutral line reference voltage in most AC distribution systems and a zero voltage for DC distribution systems.
As a precaution, modern safety switches for residual current circuit breakers reduce the need for Earthing by comparing the difference between the current flowing on the active and the neutral line and switching off the power to the active current if they differ only by a few milliamperes. The current in the active and neutral lines should always be the same, unless the circuit is broken.
