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The resistance path is the total resistance back through the supply transformer; to measure this an engineer will use an "earth fault loop impedance meter". The application of a low voltage allows a small current to pass from the socket back through earth to the supply transformer and distribution board.
Live testing. Earth fault loop impedance testing: this test is to check that if a fault did occur, that the system meets requirements to cause a disconnection of the supply within the time limit specified by standards Insulation resistance testing Polarity test: a test to check that the connections are connected in the right sequence
Multifunction testers are able to perform continuity tests (or low ohms resistance tests) and insulation resistance tests (or high ohms resistance tests) and they may also be able to perform earth fault loop impedance tests, prospective short-circuit current tests, earth electrode tests and RCD tests.
In an electric power system, a fault or fault current is any abnormal electric current. For example, a short circuit is a fault in which a live wire touches a neutral or ground wire. An open-circuit fault occurs if a circuit is interrupted by a failure of a current-carrying wire (phase or neutral) or a blown fuse or circuit breaker .
A ground loop is caused by the interconnection of electrical devices that results in multiple paths to ground, thereby forming closed conductive loops through the ground connections. A common example is two electrical devices each connected to a mains power outlet by a three-conductor cable and plug containing a protective ground conductor for ...
A ground conductor only carries significant current if there is a circuit fault that would otherwise energize exposed conductive parts and present a shock hazard. In that case, circuit protection devices may detect a fault to a grounded metal enclosure and automatically de-energize the circuit, or may provide a warning of a ground fault.
Earth fault protection also requires current transformers and senses an imbalance in a three-phase circuit. Normally the three phase currents are in balance, i.e. roughly equal in magnitude. If one or two phases become connected to earth via a low impedance path, their magnitudes will increase dramatically, as will current imbalance.
An earth-leakage circuit breaker (ELCB) is a safety device used in electrical installations with high Earth impedance to prevent shock. It detects small stray voltages on the metal enclosures of electrical equipment, and interrupts the circuit if a dangerous voltage is detected.