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Minimum values of insulation resistance

Wombat
What is the science behind the 1 MOhm minimum insulation resistance? What is the basis for this particular value?
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    It matches perfectly the permitted touch current for double insulated appliances (0.5 mA) for a supply voltage U0 of 500 V.



    But why would we then apply the same value to a 230V installation?


    Or indeed to only part of an installation - as I recall, the 1MΩ limit is for one DB and its outgoing circuits (with all appliances disconnected, even fixed ones).


       - Andy.
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  • 0

    It matches perfectly the permitted touch current for double insulated appliances (0.5 mA) for a supply voltage U0 of 500 V.



    But why would we then apply the same value to a 230V installation?


    Or indeed to only part of an installation - as I recall, the 1MΩ limit is for one DB and its outgoing circuits (with all appliances disconnected, even fixed ones).


       - Andy.
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