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Minimum values of insulation resistance

Wombat over 5 years ago

What is the science behind the 1 MOhm minimum insulation resistance? What is the basis for this particular value?

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0 gkenyon over 5 years ago

mapj1:

Is an NE fault immedately dangerous, potentially dangerous, or just extremely annoying if it causes nuisance tripping ?

Personally, I think without another fault, such as an open CPC - which may come with the cable damage (rings are nice as you can test for that) or LN reversal, it is probably more of a pain than an immediate danger.

In a TN-C-S or TN-S installation that is supplied in accordance with ESQCR, an N-E fault could be considered a breach of legislation, as both conductors effectively become parallel PEN conductors. In a TT system, an N-E fault alters the supply earthing arrangement, and again effectively could be considered a breach of legislation.

The reasons I think it could be considered immediately dangerous are:

(i) Permits diverted Neutral currents, potentially affecting touch voltages on exposed-conductive-parts, and possibly extraneous-conductive-parts.

(ii) Uncertain behaviour of protective devices - especially RCDs.
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0 gkenyon over 5 years ago

mapj1:

Is an NE fault immedately dangerous, potentially dangerous, or just extremely annoying if it causes nuisance tripping ?

Personally, I think without another fault, such as an open CPC - which may come with the cable damage (rings are nice as you can test for that) or LN reversal, it is probably more of a pain than an immediate danger.

In a TN-C-S or TN-S installation that is supplied in accordance with ESQCR, an N-E fault could be considered a breach of legislation, as both conductors effectively become parallel PEN conductors. In a TT system, an N-E fault alters the supply earthing arrangement, and again effectively could be considered a breach of legislation.

The reasons I think it could be considered immediately dangerous are:

(i) Permits diverted Neutral currents, potentially affecting touch voltages on exposed-conductive-parts, and possibly extraneous-conductive-parts.

(ii) Uncertain behaviour of protective devices - especially RCDs.
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