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Topic Title: Low insulation test
Topic Summary: Low insulation test
Created On: 08 December 2013 04:58 PM
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 08 December 2013 04:58 PM
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nige296

Posts: 74
Joined: 04 December 2009

Any tips on the best way of investigating/fixing a bad insulation test on earth/neutral and line/earth on a ring main and a lighting circuit. (circuits were tested individually and all plugs and bulbs out, neutral and line connected together tested to earth) all the results were below 1mega ohm.
 08 December 2013 05:37 PM
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KFH

Posts: 204
Joined: 06 November 2010

Split the ring into roughly half and see which half the fault is on and then spilt that half further. Same with lighting circuit. You should eventually find which leg the fault is on and can try to identify where the fault is.

I hope you have better luck than me last week with low IR on a ring. Nearly every socket had been plastered in and when I did get them out the majority were spurs off the ring or spurs off spurs. Most of the ceilings were exposed so trying to find where the cables ran was a nightmare, diagonally across walls, along skirting etc feeding both upstairs and downstairs. Eventually traced it to an unfused spur running via SWA (terminated in a wall) to a garage which then had a variety of spurs off the SWA via round junction boxes for lights, power, with further extensions to greenhouse and shed all running off the originall ring 32 A breaker for which the Zs in the garage was to high.

I have thought about breaking the ring into two radials but am not sure I have actually found any sockets which are on the ring. DId find the imersion heater run as a spur off the ring. These are problems for next time I am there.
 08 December 2013 07:56 PM
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DOUGIE1000

Posts: 4153
Joined: 13 August 2005

As KFH said, split it test and split again til your left with both ends of cable that a low

-------------------------
Dougie
Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!
 09 December 2013 11:07 AM
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AJJewsbury

Posts: 11271
Joined: 13 August 2003

Are you sure there wasn't something still connected somewhere? (A 'surge protected' extension lead is a favourite)
- Andy.
 09 December 2013 05:05 PM
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KFH

Posts: 204
Joined: 06 November 2010

A good point from Andy. Surge protectors give a good result at 250V and a very poor result at 500V which is a good indication that you need to go and find them. Is it only me or are they usually plugged in behind a piece of furniture, usually screwed to the wall, that is nealry impossible to move.
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