Electrical Craft Practice - Installation, Testing and Maintenance
This domain tests your hands-on competence: installing to the National Rules, isolating and proving dead, carrying out the standard tests in the correct order, recording results on the certification, and keeping existing installations serviceable through planned maintenance and systematic fault-finding.
Test sequence
Dead tests come before live tests, always:
- continuity of protective and main equipotential bonding conductors, and of circuit protective conductors;
- continuity of ring final circuit conductors (r1, rn, r2);
- insulation resistance at 500 V DC, minimum 1 MΩ, main switch off and sensitive loads, SPDs and dimmers disconnected;
- polarity.
Live tests follow: earth fault loop impedance (Zs), RCD operation, and functional checks.
RCD checks
At half rated residual current the device must not trip; at IΔn it must trip within 300 ms; at 5 IΔn within 40 ms for a 30 mA device. Test on both half-cycles with a calibrated instrument and record the measured times, not just the word "pass".
Worked example
A 32 A ring final in 2.5 mm² line and neutral with a 1.5 mm² CPC gives end-to-end readings r1 = 0.40 Ω, rn = 0.42 Ω, r2 = 0.65 Ω. Expected at any socket: (r1 + rn)/4 = 0.205 Ω and (r1 + r2)/4 = 0.263 Ω. The tester reads 0.31 Ω at one outlet - above the calculated value and outside the ±0.05 Ω tolerance normally applied - so either the ring is open or the termination is loose at that point. Re-make the connection and re-test rather than accepting the reading.
Traps
Proving the voltage indicator before work but not after; leaving electronics in circuit during insulation resistance testing (false low readings or damage); testing an RCD only at IΔn; confusing r1 + r2 with R1 + R2; and completing a schedule of results without stating the instrument used or the test conditions.