Earthing is a safety device used to prevent a shock due to leakages arising from weak insulation, breaking of the element or otherwise. The metal bodies of appliances handled like the electric iron, kettle or refrigerator must be earthed, that is, connected to a pipe leading deep into the earth on to a metal plate. In case the metal body becomes live, the circuit is completed through the live wire and the earth, resulting in a high current. The fuse on the live-wire side should blow out immediately, and the matter should be investigated and the fault rectified. In case the fuse does not blow out, and a person touches it, a severe shock is still prevented. This is because most of the current flows directly to the earth via the earth connection which has negligible resistance. An extremely small current, if at all, may pass through the person’s body which offers a resistance, resulting in only a mild 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.