Insulation test questions

I'm changing the case on the consumer unit - replacement for broken one guv, honest - and in replacing all the original internal bits it may coincidentally become a full 17th edition box.

Before I reconnect everything I want to do a sensible set of circuit tests, that I can record. I have a query or two re insulation testing.

For rings and single function radials (oven, immersion etc) I can be fairly confident that nothing sensitive is connected, and insulation test at 500V for L-E, N-E, L-N. For lighting circuits, which include electronic items like microprocessor dimmers and 12v halogen PSUs, disconnected only by single pole switches, I'm a bit wary about using 500V testing. Other options would seem to be to test just at 250V, or to temporarily connect line and neutral and test to earth at 500V. Any thoughts?

Finally, I have mains/battery smoke detectors on their own single 6A circuit. The mains feed in 1mm T&E goes to the first detector, and thence onward in 3&E. Should there be an isolator (FCU or similar) before the first detector, and if not what are the implications here for insulation testing?

Thanks for any advice,

Charles F

Reply to
Charles Fearnley
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I suggest doing the test at 250V to start with. That way if you get a reading of zero you know something is still plugged in. I do not know what

500V would do to the PCB of an oven! Remember that if anything is connected no matter how sensitive then the LN reading will be very low.

You suggestion for the lights is correct. Although you can also do a 500V test if all the lights are turned off - it just means you are not fully testing the switch wires.

As for the smokes. I see no reason for them to have an isolator.

Reply to
ARWadsworth

Thanks Adam - really useful to have a comment from someone who does this all the time.... I'll start with 250v on everything to confirm nothing has been missed or left switched on.

As for the lights - not dealing with new installations it had not occurred to me that with no lamps installed the switches can all be on and all cables tested. In an existing installation I can't see many people wanting to completely de-bulb, so testing at 500v would be just the "backbone" wiring with switches off - this is how the electrical contractor who tested my earlier work for the council did it.

Charles F

Reply to
Charles Fearnley

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