Testing, Verification, Commissioning and Certification
Verification is a sequence, and exam questions test order and interpretation. Before energising: visual inspection, then continuity of protective earthing and bonding, insulation resistance, polarity, and fault loop impedance (or earth fault loop verification); after energising: RCD trip tests, functional tests, and confirmation of correct operation. AS/NZS 3017 gives the practical test methods.
Key concepts: insulation resistance measured with the correct test voltage (typically 500 V DC for low-voltage circuits) and minimum acceptable values; continuity tests using a low-resistance ohmmeter with the circuit isolated; polarity checks ensuring active and neutral are correct at every point; and RCD tests confirming trip time and current. Commissioning includes verifying discrimination and load balance, and documenting results.
Traps: performing insulation resistance with electronics connected (damage or false readings); testing fault loop impedance before confirming polarity; accepting a single RCD test push as proof (you must test trip time and current); and certifying before all results are recorded. Certification must reflect actual measured values, not assumed ones.
Worked example: After installing a new submain, you isolate, verify earth continuity, measure insulation resistance (≥1 MΩ at 500 V), check polarity, then energise and measure Zs. If Zs exceeds the table limit for the protective device, you do not certify - you correct the earth path and retest.