Straight to the final test

03Energise and test

Dead first, then live, then in writing

Testing is the part of the job where the work either proves itself or does not, and the order the tests are done in is not a matter of taste. Everything that can be proved with the installation isolated is proved first, because a fault found dead cannot hurt anybody.

The dead tests

With the supply isolated and proved dead, continuity of the protective conductors and of the main and supplementary bonding is measured, and on any ring final circuit the three continuity readings that prove the ring is actually a ring are taken rather than assumed. Insulation resistance follows. That one matters more than its reputation suggests: it is the test that finds the screw a kitchen fitter put through a cable, the nail behind a curtain rail, and the conductor crushed under a box lug — and it cannot be done once the installation is live.

Polarity is proved dead as well as live, so that a switch found in a neutral is found before anybody is relying on it. Where there is any doubt about what was there before the work started, that is measured too and written down as found rather than quietly improved.

The earth fault loop, drawn as a circuit A loop starting at the supply transformer, through the supply conductor to the consumer unit, out along the circuit line conductor to an accessory, and back through the circuit protective conductor and the earthing arrangement to the supply. The path is the one an earth fault current would take. supply unit accessory line protective conductor earthing arrangement
Loop impedance is a measurement of this whole path, which is why it is taken at the accessory and not at the unit.

The live tests

Only when the dead tests are clean does the installation get energised. Polarity is confirmed again at the accessories, earth fault loop impedance is measured at the far end of each circuit where it is worst rather than at the unit where it flatters, prospective fault current is established, and every residual current device is operated and timed instead of being trusted because it clicks.

Readings go down as they are taken. A figure written from memory at the end of the day is not a measurement, and an installation whose results were reconstructed afterwards cannot be compared with its own results in five years, which is the main thing results are for.

Handover, and what this company does not claim

The client is given the certification the work calls for, the measured results that belong with it, and a plain account of anything found that was already there before the work started and has been left as it was. Where domestic work is notifiable under Part P of the Building Regulations, the route to a certificate is the local authority's building control, and that is arranged and said plainly before the job starts.

MYKIN LIMITED holds no competent-person scheme membership and makes no claim to self-certify notifiable work. Work is carried out to BS 7671 and to Part P as the rules it is done to, which is a different statement from being approved under either, and the difference is the whole point of writing it here rather than leaving it to be assumed.

  1. Isolate, and prove dead
  2. Continuity of protective conductors and bonding
  3. Continuity of ring final conductors
  4. Insulation resistance
  5. Polarity, dead
  6. Energise
  7. Polarity confirmed at the accessories
  8. Earth fault loop impedance, and prospective fault current
  9. Operating times of every residual current device
  10. Functional checks, then the written results and the certification

Back to the sequence, or read what this company keeps.