In electricity supply systems, an earthing system
defines the electrical potential of the conductors relative to the Earth´ s
conductive surface. The choice of earthing system can affect the safety and
electromagnetic compatibility of the power supply, and regulations can vary
considerably among countries. Most electrical systems connect one supply
conductor to earth (ground). If a fault within an electrical device connects a
"hot" (unearthed) supply conductor to an exposed conductive surface,
anyone touching it while electrically connected to the earth (e.g., by standing
on it, or touching an earthed sink) will complete a circuit back to the earthed
supply conductor and receive an electric shock.
For an earth connection, a three-pin socket and plug are required. Due to the
high current it draws, the earth pin is made thicker and larger than the other
two pins. This ensures that the plug fits firmly into the socket, reducing the
chances of sparking. The heat caused by sparking causes the terminals to wear
off and damages the socket and the plug. Because it is larger, the earth
connection is made first acting as a safety device.