Earthing system

A protective earth (PE) connection ensures that all exposed conductive surfaces are at the same electrical potential as the surface of the Earth, to avoid the risk of electrical shock if a person touches a device in which an insulation fault has occurred. It ensures that in the case of an insulation fault (a "short circuit"), a very high current flows, which will trigger an overcurrent protection device  that disconnects the power supply.

A functional earth connection serves a purpose other than providing protection against  In contrast to a protective earth connection, a functional earth connection may carry a current during the normal operation of a device. Functional earth connections may be required by devices such as and  filters, some types of and various measurement instruments. Generally the protective earth is also used as a functional earth, though this requires care in some situations.

In systems, an  system defines the of the conductors relative to that of the Earth's conductive surface. The choice of earthing system has implications for the and of the power supply. Note that regulations for earthing (grounding) systems vary considerably among different countries.