OP
NickD
Just a thought, did you zero your meter correctly with the plug lead on?
Indeed I did.
Discuss When Is 0.5ohms Not 0.5ohms? in the UK Electrical Forum area at ElectriciansForums.net
Just a thought, did you zero your meter correctly with the plug lead on?
the test voltage your using is prone to false negatives when testing through sockets
how can it be justified to say your going to fail it when it passes ELI at socket front but fails R1+R2 at socket front
Thats what the Plug in ELI check will confirm ..forget its a socket and tell me how would you do the test (cooker point, spur etc ) your drop it forward and your point is really lost as what if the spur contacts are the same etc you would still miss them through routine testing. I admire anyone who goes this deep to understand their career as many don't give it a thought but try not to overthink this one..we are here to ensure safety and as of yet y advise would not compromise safety merely give you more flexibility in deciding if to pass a circuit or fail it.Flipping the coin, what you're saying is that the resistance is heavily non-ohmic, and so we should trust that a resistance that is quite clearly there when accurately tested with low test voltage will become negligible when 230V is applied. I don't see any reason to go with that hypothesis, but if you have one I'd like to hear it. Plus we know bog all about the nature of the resistance (slack contacts? tarnish? oxidation? general muck?) so how can we make confident predictions that it'll start conduction happily at 230V?
I suppose the bigger philosophical questions is whether the fixed wiring system ends at the terminals at the back of the socket or the socket receptacles at the front....
Actually the 30/32 A OCPD (and Zs) is to protect the RFC
Im not telling you to totally rely on ELI results against obscureR1+R2 Im saying evaluate any difference and do a few small checks to ensure the socket isn't the cause then make an educated judgement to whether fail or pass the circuit on the merits of the front and rear results.Because the other thing that's different between those two scenarios, as well as the test voltage, is the presence of parallel paths. R1+R2 done properly is immune to them, ELI is at their mercy. I would bet my car that I'd have failed my 2394/2395 if I'd live tested Zs at a socket then used it as a Schedule Of Tests sheet result.
Because the other thing that's different between those two scenarios, as well as the test voltage, is the presence of parallel paths. R1+R2 done properly is immune to them, ELI is at their mercy. I would bet my car that I'd have failed my 2394/2395 if I'd live tested Zs at a socket then used it as a Schedule Of Tests sheet result.
forget its a socket and tell me how would you do the test (cooker point, spur etc ) your drop it forward and your point is really lost as what if the spur contacts are the same etc you would still miss them through routine testing.
I admire anyone who goes this deep to understand their career
These measurements are taken getting towards the arse end of the instrument's range.
Then there are all the errors to take into account, probe contact, etc. etc. etc.......
I have a socket that passes both R1 + R2 and ELI then i plug in a 30m extension that means the extension outlet falls well below pass value if i tested from it! ...where do i stand then????
I am not so sure on that statement, when I did my 2391 it was generally accepted that the measured Zs could be different from the measured/calculated Zs= Ze + (R1+R2), usually lower due to parallel paths.
Should have seen that coming good response ...my bed time cheers! :stooge_curly:
Indeed, and that's the point, parallel paths can offer an unfair assist to help pull a Zs assessment down below the maximum value. Go back to basics - why when taking a Ze measurement at a DB do we not just clip onto the earth bar or MET, but instead have to whip out the earthing conductor and clip onto that? This is a standard assessment test/check in exams, practicals, Part P registration assessments and not doing it or not knowing why you do it is a good way to crash and burn. Not placing reliance on parallel paths in other situations is just an extension of that logic.
I did say there were two schools of thought on this
BS7671 deems either method to be acceptable
Then why give you a choice of (R1+R2) or R2 on the schedule of test results ?
The Ze measurement is slightly different
I take it you are fairly new to testing then ?, and/or limited to domestic ?
(GN3) P52 gives ......
1) 'Live' Zs is made with neither bonding or earth removed.
2) Zs can be a measured value or a calculated value.
OSG P162 also mentions test or measure for Zs ....
it's a bit like hunting down a fault isn't it? sometimes you don't find it with 230 but IR at 1000v and all is revealed.
Well well. I have to admit to being pretty gobsmacked about them being apparently so relaxed about their implied suggestion of "just measure Zs if that suits your mood, don't worry about how much of the R2 is actually a parallel path through a boiler that's being ripped out next week".
.... "just measure Zs if that suits your mood, don't worry about how much of the R2 is actually a parallel path through a boiler that's being ripped out next week".
That is because you are thinking in terms of domestic with only a few circuits. The second method is allowed because that may be the only way to test a larger install.
No, I do understand that, absolutely; but my point is, why not clearly point out the parallel paths risk that comes with the direct Zs measurement rather than declare it to be a matter of personal taste? Something like "Measure Zs direct by all means if you must, but beware the parallel path Jabberwock, my son."
I think it boils down to you can't predict whats going to happen in the future, you can only play with the cards dealt to you now!
Plus of course we all know people only use "competent/registered tradesmen" to do their work for them. And through their training and experience these tradesmen would clearly be appreciative of the problems they could cause .....
Because as a "competent person" you are supposed to know this, lol, GN3 and associated literature is only to guide you as far as the regs are concerned, it not meant to teach you how to T&I, only how to comply with the requirements of BS7671.
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