Testing IR on a ring main

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Do all plugs need to be out of the sockets or can they be just switched off? Would an extension cable with a neon light affect the reading if left in a socket?
 
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All unplugged, not all socket outlets are DP switched.
 
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If the reading live to earth is low what other causes besides a neon could there be?
Is live to neutral testing usually avoided even if absolutely everything can be removed from the circuit?
 
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If the reading live to earth is low what other causes besides a neon could there be?
how low is it, and what is the neutral-earth IR? Is this just one circuit, a whole installation or what?
Is live to neutral testing usually avoided even if absolutely everything can be removed from the circuit?
It is probably "usually avoided' since it is often impossible to be totally certain/confident that "absolutely everything has been removed from the circuit" - but, if one feels that one is "totally certain/confident" that such is the case, then there's no reason why it can't/shouldn't be done.

Kind Regards, John
 
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AIUI surge protected extension leads often have surge protection components that will activate on a 500V IR test and give a low reading. At least in some cases these are installed in all three positions.
 
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34 MΩ on the upstairs ring. The test showed this on live to earth. I had left two extension leads, one surge protected, plugged in. Both have neon indicators.
 
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Looking at the range, 34Meg is low, but electrically, it is a pass.

To give a quick idea of insulation resistance on an installation, I used to do a global IR, putting L & N together and testing to E.
 
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He didn't want to do that due to some fixed appliances. Wired-in timer and alarm system were mentioned but there were others I think.
 
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Both have neon indicators.

Neons would directly affect Live to Neutral IR readings as they are connected between Live and Neutral and not to Earth,

That said as Earth and Neutral are connected together at the cut out then anything that affects IR readings Live to Neutral will also affect IR readings Live to Earth.
 
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34 MΩ on the upstairs ring. The test showed this on live to earth. I had left two extension leads, one surge protected, plugged in. Both have neon indicators.
It would take only a tiny amount of moisture, remnants of a dead insects or whatever to get an IR than 'low' - I don't think many people would be concerned about it.

I would expect a neon to bring about a result appreciably less than 34 MΩ with an L-N test (but not L-E - unless the neon connected L-E, which would be 'naughty', but has been known to be done when there is no neutral available!).
He didn't want to do that due to some fixed appliances. Wired-in timer and alarm system were mentioned but there were others I think.
If one tests between L+N and E, a 'fixed load' will only affect the IR measurement if any of the loads have an L-E or N-E 'leak', and that's probably unlikely with the sort of loads you mention. In any event, there's no harm in trying - if one gets a very high result, then one is re-assured and, if not, one can 'investigate further'.

The 'danger' with (actually to) connected loads arises when one does IR testing between L and N (or sometimes even between L and E) - since a 500V IR test may (depending upon what they are) damage/destroy such loads.

Kind Regards, John
Edit: clarified
 
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Neons would directly affect Live to Neutral IR readings as they are connected between Live and Neutral and not to Earth
I have a couple of extension leads I got from a previous job when they were thrown out for failing PAT. Reason they failed was due to the neon being between L&E and hence failing at 500V. Could also be surge protected, in which case the MOVs would conduct before 500V is reached.
I think (well guess, no idea if they came with destructions) the idea was that if there was no earth then the neon wouldn't light and the user would realise there's a problem and investigate. Hmm, there's a little voice suggesting there might be a problem with that idea :whistle:

From memory, the internal arrangement made re-connecting the neon L-N was a bit fiddly.
 
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... thrown out for failing PAT. Reason they failed was due to the neon being between L&E and hence failing at 500V. ... I think (well guess, no idea if they came with destructions) the idea was that if there was no earth then the neon wouldn't light and the user would realise there's a problem and investigate. Hmm, there's a little voice suggesting there might be a problem with that idea :whistle:
I must say I've never come across that one. As I hinted a couple of posts back, I've certainly see occasions on which neons have been installed L-E when there was no neutral available (e.g. at a light switch), but there's really no excuse with an extension lead - particular since, as you admit, there would be a major flaw in the possible 'thinking behind it' that you 'guess at' above!

Kind Regards, John
 
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The 'danger' with (actually to) connected loads arises when one does IR testing between L and E - since a 500V IR test may (depending upon what they are) damage/destroy such loads.
Is that correct John :)
I thought that the danger was when you test L to N
 
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The 'danger' with (actually to) connected loads arises when one does IR testing between L and E - since a 500V IR test may (depending upon what they are) damage/destroy such loads.
Is that correct John :) I thought that the danger was when you test L to N
"L-N" is indeed, what I intended to type - so just a typo (now 'clarified') :) Thanks for noticing.

I say 'clarified' (rather than 'corrected') since I think that, even with L-E testing there is sometimes a potential risk (to connected 'sensitive' loads). For example, if there is an N-E input 'filter' capacitor in the load, then when one connects 500V DC between L and E, 500V will presumably transiently appear between N and E - potentially for long enough to damage or kill a sensitive load.

Kind Regards, John
 
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