2391-101 Inspection, Testing and Certification of Electrical Installations

2391-101 Inspection, Testing and Certification of Electrical Installations is according what I have read on the Internet and heard form those that have already taken the exam difficult to pass. The City and Guilds website only confirms the evidence. It would seem that less than half of those taking the exam pass.

Well it appears that I have to sit the examination, after first doing a three day course and also a one day practical. Before I commence the course I thought I would get familiar with what will be required to pass.

The chief examiner's report gives some indication as to where some easy marks can be gained.

One such area is in the sequence of testing. It makes logically sense that before power is applied to a circuit that it is tested since the testing could highlight any possible dangerous faults.
Isolate and Check was a slogan used in the mining industry. Before touching the wiring I would prove my voltage indicator, verify that the circuit or circuits are dead by testing at a few different points, once satisfied, verify that the voltage indicator still works. (Using a proving unit).
So which test comes first? Well what is the point of doing an insulation test if there in an open circuit on the phase, neutral or circuit protective conductor since any test would be meaningless. So in I am correct in my theory then the continuity of the conductors needs to be established.

For a simple circuit R1 + R2 is the phase conductor + the CPC impedance values and will be in ohms subtract from this any value for the leads that were obtained on the instrument check. The neutral should have the same csa of the phase conductor and should be almost equal to that of the phase impedance depending upon the circuit arrangement. For a three phase circuit the highest impedance is the one that could prevent a protective device operating thus this is the one used in practice against the chart to determine whether or not the reading is low enough and therfore recorded. Polarity can be checked at this point by making sure that single pole switches break the phase conductor and not the neutral or CPC.
Once continuity of all possible circuit combinations have been recorderd I would guess that each circuit is tested for insulation resistance using the 500V range of an insulation tester for domestic premises. Although the leads should be shorted together to verify the meter reads zero, I prefer to place one lead on an earth and then verify my contact by connecting the other lead to another earth location close by. Since all wiring would need to be tested it is important to have all the switches are turned on. Where there is two lighting circuits this means that all combinations of the switching needs to be verified. I doubt the exam would go beyond the simple two way circuit.
A reading of zero Megohms could indicate that a shorting wire is still in place or that there is a fault. If a low test is obtained between phase and neutral it could be that a neon is used on a fused spur or that a genuine fault is present.

If tests revealed a fault and I resolved the problem then I would begin the tests again in case during my investigations I had inadvertently disturbed the wiring.

more later, (eyes are tired)