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Regulation 643.3.3 (ii) clarification

DR Darren Hughes

I want to ask if someone can help clarify the requirements on the regulation 643.3.3, notably the second para  (or ii in GN3)

Whilst it is understood that an initial insulation resistance test should be carried out with all Sensitive loads disconnected, once they are reconnected the regulation reads "Following connection of the equipment, a test at 250 V DC shall be applied between live conductors and the protective conductor connected to the earthing arrangement."

Does this mean we are conducting two separate tests, i.e. line to CPC and Neutral to CPC? Or a single test where we link line and neutral, then test that to CPC (i.e. like previous guidance). I suspect it is the letter, but would be grateful for your thoughts.

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    Chris Pearson refers to the "second test" which is all lives connected together to earth as a short cut, it is not a short cut, it ensures the entire installation has a satisfactory insulation test value. This part of the testing should be done at 500 vDC before sensitive loads are connected and again at 250 vDC when the sensitive loads that cannot be isolated are connected.

    The mininium test result value of one megohm is for the entire installation and the entire installation should be tested all at the same time to earth.

  • 0 in reply to Sparkingchip

    Note that the 1meg limit is a bit arbitrary, as what to expect  is rather installation dependent Of course large rambling installations on farms with lots of damp sheds or anywhere with a lot of pyrotenax mineral insulated cable (churches  are good candidates), are likely to fail with no fault found, while a short PVC lighting circuit in a small bedsit flat ought to be a hundred meg or more really and should raise an investigation at more like 10meg. So don't be too black and white about it.

    Mike

    PS to pass the farm/ damp church it may be necessary to review it in zones each of which individually pass.

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  • 0 in reply to Sparkingchip

    Note that the 1meg limit is a bit arbitrary, as what to expect  is rather installation dependent Of course large rambling installations on farms with lots of damp sheds or anywhere with a lot of pyrotenax mineral insulated cable (churches  are good candidates), are likely to fail with no fault found, while a short PVC lighting circuit in a small bedsit flat ought to be a hundred meg or more really and should raise an investigation at more like 10meg. So don't be too black and white about it.

    Mike

    PS to pass the farm/ damp church it may be necessary to review it in zones each of which individually pass.

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