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Minimum values of insulation resistance

What is the science behind the 1 MOhm minimum insulation resistance? What is the basis for this particular value?
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  • I'm not saying an NE short is a good thing - far from it, but If all it does is lower R2 or trip an RCD prematurely above some modest level of load, then is only being a pain to the user, not the same 'immediate ' danger comparable to exposed live parts.

    Only a really badly designed system becomes dangerous in a power cut and I'd hope they have back up power or some pre-arranged back-up supply.

    And as noted above, when we started putting RCDs in, quite a lot of dormant N-E faults were found and had to be fixed, suggesting they had been around a while.
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  • I'm not saying an NE short is a good thing - far from it, but If all it does is lower R2 or trip an RCD prematurely above some modest level of load, then is only being a pain to the user, not the same 'immediate ' danger comparable to exposed live parts.

    Only a really badly designed system becomes dangerous in a power cut and I'd hope they have back up power or some pre-arranged back-up supply.

    And as noted above, when we started putting RCDs in, quite a lot of dormant N-E faults were found and had to be fixed, suggesting they had been around a while.
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