Wiring Accessories Minimum values of insulation resistance
Circuit nominal voltage (V)
Up to and including 500 V with the exception of SELV and PELV systems
Test voltage DC (V)
Minimum insulation
resistance (MΩ)
500
1.0
stated values is preferred (643.3.2). Regulation 641.1 requires that every installation is tested both during erection and on completion before being put into service. Insofar as this relates to insulation resistance testing, this means that tests should be carried out after first fixing (after cables have been installed and prior to equipment being connected). This test confirms that the installed cables are in a fit state. The final insulation resistance test needs to be carried out after second fixing has taken place. However, after second fixing it may be that connected equipment may influence the measurement or result of the test (643.3.3). Where this is the case, following the connection of equipment, it is permitted to reduce the test voltage to 250 V DC and to test between the live conductors (connected together) and Earth.
Figure 2: Testing between live conductors
Sensitive electronic equipment The note attached to Regulation 643.3.3 indicates that manufacturer’s instructions may recommend some equipment needs to be disconnected even when the test voltage is reduced to 250 V DC. This may apply, typically, to accessories such as socket-outlets with USB connections and the like. Scolmore’s Click socket-outlets with USB ports do not require disconnecting and may be tested between live conductors (connected together) and Earth at a test voltage of 500 V DC whilst still connected in circuit.
Conclusion
Insulation resistance testing is an essential part of ensuring that prior to energisation the installation is safe. The tests verify that there are no inadvertent connections between live conductors and between live conductors and Earth. Care should be taken to ensure that any connected equipment is capable of withstanding the test voltages applied. Where there is a risk of damage or test results outside of the permitted range, it may be necessary to disconnect equipment prior to any test being carried out.
ewnews.co.uk May 2023 electrical wholesaler | 25
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44
