Inspection, Testing and Certification
Core concepts
You must know the sequence of inspection and testing: visual inspection first, then dead tests (continuity of protective conductors, ring final circuit continuity, insulation resistance, polarity), then live tests (earth fault loop impedance, RCD operation, functional testing). Understand instrument types - low-resistance ohmmeter, insulation resistance tester, loop impedance tester, RCD tester - and the need for proving instruments before and after use. Know what a certificate records, who signs it, and the difference between initial verification and periodic inspection.
Traps
Questions often reverse the order of tests, or ask what to do if an insulation resistance reading is low (investigate, do not just record). Another trap is failing to isolate before dead tests, or testing insulation resistance with electronics still connected. Watch for questions about test results that are 'acceptable' - you must know the minimum values and the conditions under which they apply.
Worked example
Insulation resistance is measured between live conductors and earth with the supply isolated and loads disconnected. A reading of at least 1 MΩ is generally required for a standard circuit; a lower reading means finding and removing the cause before energising. Always record the actual reading, not just 'pass'.
Rule of thumb
Inspect before you test, test dead before live, and prove your instrument before and after every measurement.