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Re: Electricity supply cable: why are E and N combined? |
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| message from Martin Angove on 10 May 2004 |
The scary thing about PME is that there is a possible failure mode where
the power is off, but everything is still live, and unearthed. This
would be the case where somehow someone cuts through the supply
company's neutral just before it enters your house, but not the live.
As has been said, the supply company goes to great lengths to earth the
neutral (hence "multiple") as securely as possible to prevent this, and
the use of concentric cable makes it extremely unlikely, but having PME
makes it even more important that main and supplementary bonding is
correctly used.
Actually, come to think of it, there is a possible failure mode in a
TN-S system where the earth disappears but L&N are still live. That
could be quite dangerous too, if a fault develops in your
installation...
Maybe we should all go back to candles :-)
Hwyl!
M.
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| Christian McArdle replied to Martin Angove on 10 May 2004 |
Indeed. It is more dangerous than the PME case, as with PME you would have a
power cut that causes the fault to be fixed. If you lost only the earth but
not the neutral, you could continue in that state for some time without
anyone realising that a fault has occured.
Christian.
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Archived message: Re: Electricity supply cable: why are E and N combined? (UK D-I-Y House Improvement)
