Inspection, Testing and Certification to BS 7671
Inspection, Testing and Certification to BS 7671
Part 6 and Chapters 61-63 govern initial verification and periodic reporting. The exam favours sequence, test method and interpretation of results over memorised numbers alone.
Sequence and certification
Visual inspection comes first, then dead tests (continuity of protective and bonding conductors, ring final continuity, insulation resistance, polarity), then live tests (earth fault loop impedance, RCD operation, prospective fault current), then functional testing. Certificates: an EIC for new work, an MEIWC for minor work, an EICR for condition reporting, each supported by a schedule of inspections and a schedule of test results.
Key values
Insulation resistance at 500 V DC with a minimum of 1 Mohm (250 V DC for SELV and PELV). RCD: no trip at half the rated residual current, trip within 300 ms at the rated current, within 40 ms at five times it. Ring final continuity is proved using r1, rn and r2 with the ends cross-connected.
Worked example
A 2.5/1.5 mm2 ring final gives r1 = 0.42 ohm, rn = 0.41 ohm, r2 = 0.68 ohm. The expected end-to-end CPC reading is about r1 x (2.5/1.5) = 0.42 x 1.67 = 0.70 ohm, so 0.68 ohm is consistent. At each socket, R1+R2 should be roughly (r1+r2)/4 = (0.42+0.68)/4 = 0.275 ohm. A socket reading well above that suggests a spur or a poor termination; a near-zero reading at every socket suggests a short between conductors.
Traps
Insulation testing with SPDs, dimmers or surge devices left connected; testing L-N only and missing a N-E defect; recording 0.5 Mohm as a pass; failing to re-prove the tester after dead tests; issuing an EIC without the schedule of test results.