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Safe Disconnection to Undertake Work.

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Scene. An old farm building now used as a double glazing frame maker's workshop.


The supply comes from an old shed about 40 metres away, where the meter is. The old shed has some 70s/80s rusty M.E.M. isolators that feed several S.W.A. cables that exist the shed in many directions underground. I suspect that one feeds the main farmhouse, another a rented cottage and the others various farm buildings. There is no clear labelling of the isolators.


What is the best way to locate the frame maker's  building supply where I have to work?


Somewhere I have a circuit i/d set, if I can find it, but that will need access to the live parts and I do not wish to turn off the wrong isolator.


Z.


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  • 0
    mapj1:

    -----

    If you are brave you could try injecting a modest current onto the armour - ideally you'd need to lift the earth at the load end and that may not be possible or safe.

    However,  assuming the armour is the CPC, or at least part of the CPC, then  pulling an L-E fault current of a few amps ought to allow the correct SWA to be isolated with nothing more than  a clamp meter over the jacket of each SWA in turn to identify the one that reads more when the 'fault' current flows. Please check Zs first of course.


    Caveat, I may not have the right mental picture of the installation .

    It is of course silly to ask why are they not labelled, and what the official emergency isolation process is.

    Mike.


    Not certain that this will work. A clamp meter applied around the outer jacket of a SWA should read about zero. If the current flows "out" along the phase conductor, and "back" via either the neutral conductor or via the SWA, the NET current is still zero, excluding any minor leakages from other circuits.


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  • 0
    mapj1:

    -----

    If you are brave you could try injecting a modest current onto the armour - ideally you'd need to lift the earth at the load end and that may not be possible or safe.

    However,  assuming the armour is the CPC, or at least part of the CPC, then  pulling an L-E fault current of a few amps ought to allow the correct SWA to be isolated with nothing more than  a clamp meter over the jacket of each SWA in turn to identify the one that reads more when the 'fault' current flows. Please check Zs first of course.


    Caveat, I may not have the right mental picture of the installation .

    It is of course silly to ask why are they not labelled, and what the official emergency isolation process is.

    Mike.


    Not certain that this will work. A clamp meter applied around the outer jacket of a SWA should read about zero. If the current flows "out" along the phase conductor, and "back" via either the neutral conductor or via the SWA, the NET current is still zero, excluding any minor leakages from other circuits.


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