Table 1 Limiting values of measured earth fault loop impedance
Using this formula the maximum value of Zs that will ensure disconnection of a 32 A BS 88-3 fuse system C within 0.4 sec is 0.72 Ω (rounded down). To aid electricians carrying out inspection and testing the pads of NICEIC/ELECSA certificates contain the table of corrected values of earth fault loop impedance shown in Table 1. On this table the maximum permitted value of earth fault loop impedance is referred to as the ‘Limiting values of measured earth fault loop impedance’. It should be noted that for a 32 A BS 88-3 fuse system C fuse
the value of the Limiting value of measured earth fault loop impedance is 0.72 Ω. Whilst it is not common to carry out an earth fault loop impedance test on a circuit carrying load current, there may be instances where the circuit being tested has conductors operating at a temperature closer to their rated value, the inspector may feel that it is not appropriate to apply the 0.8 factor. In this situation the uncorrected value of limiting values of measured earth fault loop impedance can be found in Tables 41.2, 41.3, and 41.4 of BS 7671. Connections Spring 2015
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