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An earthing system, commonly called a grounding system, is used in electrical wiring to set up a ground connection. This connection serves as a safety measure to drain off the flow of electricity in the event of a short-circuit or power surge. This is accomplished through the provision of a direct connection to the Earth. Earthing systems are designed in two varieties: the protective earth and the functional earth.
For most applications, the earthing system is designed to protect the end-user from electrical shock in the event of a short-circuit. This system provides a ground wire between all electrically conductive surfaces and the Earth or ground wire of the circuit. By doing so, the electrical potential of these surfaces is matched to that of the Earth. In layman's terms, it is almost impossible to be electrocuted because the abnormal flow of electricity activates the circuit protection device. This is called a protective earth.
Another type of earthing system is the functional earth. This system is designed to protect electrical wiring and components from damage caused by a sudden power surge. A common example used to describe the function of this earthing system design is the lightning rod. The functional earth works in the same way as a lightning rod, taking the direct power surge and routing it safely to the ground. The functional earth is commonly used in surge protection devices. These devices are used to protect electrical equipment, such as computers and televisions, from lightning and power surges.
The low resistance of the protective earth is designed to produce a short burst of high current to activate circuit protection devices and shut off power to the circuit. The functional earth, however, may allow the circuit to continue to operate. Due to the high resistance of the functional earth, the circuit protection device may not be triggered. To avoid this problem, a residual current detector is installed to sense current leaking to the Earth. When leaked electrical current is detected, the device shuts the circuit down.
In most modern buildings, the earthing system is incorporated into the electrical wiring using a single-wire earth return. The single-wire earth return is simply a metal electrode that is driven into the Earth. It is attached to the main grounding wire at the electrical service meter. This single-wire earth return can provide a basic form of earthing system protection and electrical safety for a whole building. When properly assembled, the single-wire earth return functions as both a protective earth and a functional earth for an entire electrical system.