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Topic Title: new circuit
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Created On: 12 January 2015 08:54 PM
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 12 January 2015 08:54 PM
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goldenboy1818

Posts: 812
Joined: 22 February 2011

Hi on a large new ring main what insulation resistance reading would you generally expect to find. What you expect >200Mohms or less? Had a new circuit, a large ring main (end to end 0.61, 0.62, 1.03) but insulation resistance readings were all around 50Mohms between all conductors. Thanks for any advice
 12 January 2015 09:00 PM
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aligarjon

Posts: 3854
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i would expect a new ring to be clear personally.

-------------------------
Specialised Subject. The Bleedin Obvious. John Cleese
 12 January 2015 09:20 PM
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hertzal123

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Joined: 26 August 2007

Damp plaster?
Regards,Hz
 12 January 2015 09:21 PM
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daveparry1

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>500 M ohms!
 12 January 2015 09:23 PM
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daveparry1

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As Hz said, damp plaster, (probably in one of the back-boxes.)
 12 January 2015 09:34 PM
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goldenboy1818

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Yes damp plaster, what you think bits in one of the back boxes?
 12 January 2015 09:40 PM
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daveparry1

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Possibly but if the plasterer has just finished more likely to be water as well! Can you leave it to dry out for a few days and then test again?
 12 January 2015 09:46 PM
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zeeper

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Joined: 11 July 2008

if you have just installed this new circuit would be easy to break it down into quarters to see which bit was giving that reading.
 12 January 2015 09:54 PM
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leckie

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>500Mohms? My meter only goes to >299Mohms.

I would be inclined if possible, to not energise the circuit, loosen the sockets slightly, leave for a week, go back and retest. Probably be dried out a bit by then. Of course this would only apply to wet plaster spec. If it's been dry lined and skimmed, it's probably cables compressed, etc. Its considered acceptable by the regs anyway, but you would expect a single circuit to be to the maximum IR reading that your meter tests to ideally.
 12 January 2015 10:01 PM
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goldenboy1818

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How exactly does it drag the reading down, the plaster I
Mean? It's freshly plastered literally one day ago
 12 January 2015 10:17 PM
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daveparry1

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I can't believe you're asking that question Goldenboy!
 12 January 2015 10:18 PM
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Manxie

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Are the cables coiled up in the back boxes with bare ends?
 12 January 2015 10:18 PM
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leckie

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Just explain a bit more Goldenboy.

Is it full plastering, i.e. a wet plaster base coat and then skimmed, so no plasterboard?

If it was only plastered yesterday, when did you 2nd fix and test it? Do you mean it was plastered yesterday and you 2nd fixed it today?
 12 January 2015 10:20 PM
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Manxie

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What's the circuit lengths?
Sounds like you should have maybe used 4mm
 12 January 2015 10:23 PM
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Manxie

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Wet plaster base coat??
Also known as a scratch coat?
 12 January 2015 10:44 PM
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goldenboy1818

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Plastered yesterday, plasterboard first (dot and dab) then skimmed over. Sockets not screwed back just second fixed and bagged up for protection from paint etc. Won't be livened up for a while, just dead tested it to check faults etc
 12 January 2015 10:54 PM
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Manxie

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We're the sockets 'bagged up' before the plastering was done?
 13 January 2015 01:20 AM
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mapj1

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We are assuming PVC twin and earth are we not?
Clean dry and free from finger prints with salted crisps should see gigohms per hundred meters if your instruments can do that.
Damp and smeared in bacon sarnie juice at the cut ends, maybe not...

If it was pyro, or some load accessories are already added then bets are off.

Were it mine I'd go into divide and conquer mode.

namely tease the ends apart at the supply end and then break the circuit half way along. Meter from that break both left and right.
If both sides are equally leaky, well its something distributed along the length, and less likely to be serious. If its on one side only its a spot fault. Then the duff half gets opened up half way along, once again look left and right - rinse and repeat, I hope you get the idea.

PS In the past I have spent longer than I should chasing a fault that turned out to be a meter brought indoors from a cold car boot, and what I think was condensing inside and/or on the meter probes. Perhaps a quick check that its OK with just the meter leads and a tat end of cable to eliminate any instrument or probes issue.

Any chance that a plaster 'snot drop' has got into a back box ? Its pretty conductive by megohm standards.

At a very long and worrying shot, was it some bargain cable ?

-------------------------
regards Mike
 13 January 2015 07:07 AM
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leckie

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It's probably slight condensation formed on the accessories in the bags from the sounds of it.
 13 January 2015 04:42 PM
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goldenboy1818

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Literally bagged it up and tested it, so wasn't bagged long. Cable was not cheap stuff lol. Yes it is standard twin and earth, was plastered before made off ends and bagged up. Possible still bit of plaster in back box, would that drag all readings down? Will test again after its dried more, and possibly break down circuit. Just was a bit strange to get 50Mohms on new circuit. Thanks all
IET » Wiring and the regulations » new circuit

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