chapter  16
7 Pages

Testing earth fault loop impedance (regulation 612.9)

WithKevin Smith

Measurement of actual disconnection time is not really practical. The earth fault loop impedance test is performed using an earth fault loop impedance tester, which gives values in ohms. This is a 'live' test performed with the circuit connected to its supply, so great care must be taken to fully risk assess the activity and apply all necessary control measures. Calculation therefore removes the need for a 'live' test and its associated dangers. Most common earth fault loop impedance testers offer two types of tests: high current and 'no trip'. Values of earth fault loop impedance will need to be obtained at several points within the installation. The external earth fault loop impedance test is performed at the origin on the installation between the incoming line conductor and the earthing conductor. In addition to the tests performed at the origin of the installation, a measurement of earth fault loop impedance must be made at each distribution board.