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Zs, to test or calculate?

Paul Brewerton
A large contractor working on our site have told me yesterday that it is their policy not to live test final circuits where they cannot use a plug? In order to reduce risk, they will now only calculate Zs, on circuits where they would have to open an enclosure, such as FCU's and light fittings.
The control measures we insist are in place, are IP2X equipment, GS38 leads, two man rule with second man having resus training, among others. So I feel the risk has been reduced to as low as reasonably practicable. An d my instinct tells me that a measured Zs reading must be more accurate than a calculated one, since it will include all parallel paths under test.
The contractor is happy to live test distribution circuits, so it seems they want to pick and choose.
They also state that this is how things are now, and have worked at many different sites, Cross Rail, Heathrow, various MOD sites etc, and that they al accept this as common practice.

I like some opinions to find out what's going on out there on other sites. 
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    Sparkingchip:

    In the back of my van I have a telescopic fibreglass R2 testing pole, I used it to test a light on the gable of a house a couple of weeks ago, I don't intend to take an extension ladder to check a light such as that for an EICR, visual and continuity testing with both feet on the ground.


    However when replacing a light fitting and access equipment is already in place then I would loop test, as these were site cabins being installed that were already being wired before delivery to site some testing is required, if need be I would test at a switch with two feet safely on the floor, but obviously that may require a two lead loop tester and I have a couple to use.


    There is a precedent.

    https://www.manchestereveningnews.co.uk/news/greater-manchester-news/dads-agony-after-apprentice-electrician-9085985


    Andy B.


     




    We can keep going around in circles with this, the simple truth is we need to choose the time and the place to do live testing, personally I avoid doing it on top of a ladder or the like, but you may still need to prove dead.


    I remember going to look at a faulty outside light one wet winter evening, I climbed up the aluminium ladder thinking it may just need a new lamp in it and without touching the light fitting put I one probe of the voltage detector on the ladder and the other on the light fitting, it lit up like a Christmas tree so I climbed back down the ladder and started to put it back on the van, the lady customer enquired what I was doing, my reply was going home then coming back when it is light and dry as I wasn't going to mess about with it in the wet and the dark.


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  • 0
    Sparkingchip:

    In the back of my van I have a telescopic fibreglass R2 testing pole, I used it to test a light on the gable of a house a couple of weeks ago, I don't intend to take an extension ladder to check a light such as that for an EICR, visual and continuity testing with both feet on the ground.


    However when replacing a light fitting and access equipment is already in place then I would loop test, as these were site cabins being installed that were already being wired before delivery to site some testing is required, if need be I would test at a switch with two feet safely on the floor, but obviously that may require a two lead loop tester and I have a couple to use.


    There is a precedent.

    https://www.manchestereveningnews.co.uk/news/greater-manchester-news/dads-agony-after-apprentice-electrician-9085985


    Andy B.


     




    We can keep going around in circles with this, the simple truth is we need to choose the time and the place to do live testing, personally I avoid doing it on top of a ladder or the like, but you may still need to prove dead.


    I remember going to look at a faulty outside light one wet winter evening, I climbed up the aluminium ladder thinking it may just need a new lamp in it and without touching the light fitting put I one probe of the voltage detector on the ladder and the other on the light fitting, it lit up like a Christmas tree so I climbed back down the ladder and started to put it back on the van, the lady customer enquired what I was doing, my reply was going home then coming back when it is light and dry as I wasn't going to mess about with it in the wet and the dark.


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