Testing requirements for an installation
When carrying out testing on a new installation or when alterations/additions are made to an installation, a suggested sequence of testing as per AS/NZS 3000:2018 Section 8 would be as follows:
- Visual inspection of works carried out
- Earth resistance test – continuity of the main earthing conductor
- Earth resistance test for other earthed and equipotential bonded parts
- Insulation resistance test of installation
- Polarity and connections test of circuits/wiring installed e.g. consumers mains, submains or sub-circuits.
- Earth fault loop impedence test
- Verification of operation of residual current devices
Further information can be found under AS/NZS 3000:2018 Section 8: Verification.
When carrying out testing ensure all test results are recorded and records are maintained for 5 years. (ELR 1991 Reg 52 (2D)
Recently during inspections being carried out it has been found that the MEN connection has been missed during checking and testing on several installation inspections. This is regarded as a serious defect. Reason given for this has been that it is no longer a requirement to carry out earth fault loop impedence tests as circuits are now covered by RCD and the test is no longer required.
Electrical contractors and electrical workers are reminded that while RCDs can be used to achieve automatic disconnection of supply, RCDs fitted to circuits are intended only to augment other measures of basic protection and that RCD’s are additional circuit protection to that of the primary circuit protection. (AS/NZS 3000:2018 clause 2.4.1, 2.6.1)
The operation of the circuit protection is reliant upon the integrity of the MEN connection and the supply neutral (PEN) conductors. If the value of the earth fault loop impedance exceeds that of Table 8.1 AS/NZS 3000:2018 then correct operation of the primary circuit device may not be achieved. Further information on this can be found under Appendix B, B4: Protection by automatic disconnection of supply.
When completing the Electrical Safety Certificate and/or Notice of completion for electrical works carried out, electrical contractors and workers are again reminded to ensure that when completing section 4E as the completing electrical worker and signing off as the nominee that all electrical work has been checked, tested, test results recorded and certified safe to operate when connected to supply. (AS/NZS 3000:2018 clause 2.1.2 and 4.1.2, E(L)R 1991 Reg 49, 49B, 52(2B), 52(2D) and 52B.)
Note: Under certain circumstances a test for fault loop impedance could give a false impression that a MEN is present, therefore a visual confirmation of the MEN is essential.
