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EICR and IR Testing

Former Community Member
Former Community Member
Oh the bane of IR testing on EICRs

Now its just impracticle to disconnect all loads to carry out IR testing, I think everyone can agree on that. And that Phase and Neutral are connected then tested to earth.


This is what I do, and then test @250V as to avoid damaging any equipment in the installation. And unless the IR value was <.5 Meg, would not bother me. What BS7671 states, but BS7671 is maybe somewhat unclear in that if that voltage (250V) was used then .5meg value should used, but that value should only be used on SELV, and PELV. Now experience also tells me that even if you had a return 0.0, and then did Kohms by using the ohms setting, even values of 100Kohms are fine. (Actually can be much lower than this) and we are pretty clear that its not the cable reurning these values.


So question is when doing an EICR @ 250V, at what point would you recommend an FI? For me the value would have to be <.5Meg
  • 0
    Bare conductors placed out of mind does seem to be a known installation method, but not a recommended one! (some time last century we were pulling that sort of thing out, often with black cloth tape repairs as well,  clearly some is still left operational)

    The sad thing is that a cable even in that state,  laid out like that,  probably can still passes an IR test at 1000V as well as 500V, so the instruments are useful but not all-seeing -  so looking behind a few fittings at the cable itself is really important - and that cannot find the unhelpful cases where both ends have been changed, but not the hard to reach section of cable in the middle. Still, better out than in.

    edit crossed in post, but agree totally. The IR test only gets you so far.
  • 0
    John Peckham:

    Chris


    You have fallen in to the usual trap of not understanding the major difference between Initial Verification and Periodic Inspection and Testing.


    John, that's a bit unfair!


    My point was that for a periodic, L-N testing is unnecessary and as the OP said, practically impossible. How would you test a socket circuit with SRCD or USB where the manufacturer's instructions are that it should be disconnected when IR testing?


    As an aside, when testing at stages during erection, to start with the IR rapidly goes up to > 999 MΩ; but after a while it creeps up more slowly, especially when testing live to CPC. > 500 MΩ is certainly enough for me, but one could stop pressing the button as soon as it gets over 2 MΩ, or any value in between.


  • 0
    Sparkingchip:

    I went south of the river last Thursday to do what should have been a straightforward job, until I saw the cable that supplied the central heating system that I was planning to extend.


    You do have to appreciate just how bad the insulation is on some cables that are in use without tripping a RCD or MCB in a relatively new dual RCD consumer unit.


    cc3c406e19459a9746a2bb1eee2815e0-original-20200820_144553.jpg




    Going off topic, try identifying the conductors by the colour of the remnants of the insulation around them and although I said it’s rubber cable, I not actually certain that is a precise description. The house was built as a very upmarket semi-detached in one of the best locations in Greater London and this cable may be the last bit of the original installation from 1935 that was still in use, so may be eightty give years old, the rest having been rewired around sixty years ago.                                                                                                                                                                                                                                                                                            


  • 0
    That should say eighty five years old.


    This forum is very, very difficult to use on an IPad and virtually impossible to use on a phone, it really isn’t a good advertisement for the IET as leaders in a technological world.


    Andy Betteridge
  • 0
    If it is really that old it could be a vestige of a DC installation depending where exactly you were. An L-N E arrangement would not have been that common, hence all 3 cores insulated and the identical X-section. Conversion of said DC systems to what we now call TNS led to the fused neutral problem, that we have been fighting ever since.  Much earlier and it would have been more likely to be rubber covered singles served in cotton or double cotton (again, thinking of stuff I have pulled out ).

    Or it could just have been a handy bit of cable re-purposed at a time when it did not look quite so shabby.

    Pity really that rubber perishes, the tin plated copper looks to be in near perfect nick.
  • 0
    It does appear to have the red insulated conductor in the centre, which hasn’t been done for many years.


    Andy B.
  • 0
    Four areas of London still offered D.C. supplies in the late 1960’s and the last major users were theatres for arc lights and the newspapers for there printing works, with not surprisingly the last to change to the new fangled AC being the Daily Mail in 1987, entrenched in their ways as ever!


    So there are possibly still thousands of homes in London where an electrician will be trying to get a good insulation resistance value for an EICR on similar cables.

    http://www.metadyne.co.uk/pdf_files/electricity.pdf


    Andy B.
  • 0
    Sorry Chris but fairness has never been one of my weaknesses.


    IR often creeps up if the IR test button is held down especially if the installation is large as with a good IR the installation acts like a capacitor with the DC from instrument charging the capacitor. 


    I would never IR test L/L on a periodic as you can never be sure everything electronic has been disconnected and I am not keen on a claim on my insurance.
  • 0
    Andy B


    As a brand new Technical Officer straight out of the box in the Post Office I was sent to the South London Parcel Office for 2 weeks to cover for the resident TO who was on leave. It was an old grim dirty environment with all the conveyors and other kit all run on DC installed in 1935. Glass fronted face plate starters. The conveyors running from the top to the bottom of the building. One conveyor band broke and I decided to replace it rather than do another repair. 2 days of me managing a team of engineers pull in the new band and pull the ends together with winches with counter weights jacked up. Filthy dirty hard work. The visiting engineering manager was so impressed with my efforts with the team I was offered a permanent job here with promises of loads of earning opportunities. I thanked him for his kind offer and told him I wanted to get back to a job with an electronics bias, clean sitting on my bum wielding a soldering iron and an oscilloscope probe. Later I became the engineering manager for the area and went back and the old boys said words to the effect I hope you are not going to do a big belt change again!
  • 0
    John Peckham:

    Sorry Chris but fairness has never been one of my weaknesses.


    IR often creeps up if the IR test button is held down especially if the installation is large as with a good IR the installation acts like a capacitor with the DC from instrument charging the capacitor. 

    I would never IR test L/L on a periodic as you can never be sure everything electronic has been disconnected and I am not keen on a claim on my insurance.


    Including hard wired type 1 and 2 SPDs where you can do more or less nothing.

    Legh


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