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Further investigation IR below 2 Megohms or 20 Megohms??

RobW

Has the guidance on minimum insulation resistance changed in the new OSG?? I subscribe to the IET electronic versions, the current online IET OSG says that further investigation is required below 20Mohms rather than the previous versions advising further investigation below 2 Megohms? Is this just an electronic typo or has thid guidance changed.

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    Any single value is a bit of a fudge as of course it depends on how long and rambling the circuit is and what the wiring method is - pyro (MICC) cable is always a bit leaky on insulation test, as is paper insulation, but it is not faulty, but clean PVC should be giga-ohms per metre.
    I'd suggest the use of a bit of experimental  knowledge rather than blind adherence to a single figure. As far as I know it has never been 20Meg, but I do know that 1M, 2 M and 0.5M have been used by various authorities at different times. It may be that someone will chip in  with a situation that uses  20M as well ;-)
    Mike.

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  • 0

    Any single value is a bit of a fudge as of course it depends on how long and rambling the circuit is and what the wiring method is - pyro (MICC) cable is always a bit leaky on insulation test, as is paper insulation, but it is not faulty, but clean PVC should be giga-ohms per metre.
    I'd suggest the use of a bit of experimental  knowledge rather than blind adherence to a single figure. As far as I know it has never been 20Meg, but I do know that 1M, 2 M and 0.5M have been used by various authorities at different times. It may be that someone will chip in  with a situation that uses  20M as well ;-)
    Mike.

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