I'm sorry I mentioned it now!!
what size wiring- elecrtic shower
- Thread starter yellowbelly
- Start date
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So BS7671 defines "isolation" and "Isolator", does it specify that only an "isolator" can be used as a means of "isolation"? I somehow doubt it.
No, as I implied it doesn't - but it does have that whole subsection about 'Disconnection devices' in the section on Isolation.
To be serious, though, it surely is 'obvious' that when they talk about requirements for 'a means of isolation' they cannot intend that to include simple disconnection of the conductors - since that's always going to be possible one way or another, if that were acceptable, there would be no point in them requiring a 'means of isolation'. Or is that too logical? For once, I think the common sense interpretation has surely got to be the intended one.
Kind Regards, John.
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One suggestion I have seen on here for working on a single circuit is to disconnect the neutral as a matter of course, to provide double pole isolation.
Which I see as little different to the situation of working on a single circuit on a TT installation.
Which I see as little different to the situation of working on a single circuit on a TT installation.
BS7671 is a bit convoluted on the issue of isolation in TT installations. The primary requirement is for a means of isolation of all live conductors (including neutral), rapidly followed by a caveat that isolation of neutral is not required with TN-S or TN-C-S installations - i.e. effectively leaving TT as the only situation requiring DP isolation. As EFLI has pointed out, there is then an added mess in that BS7671 contains a big table of acceptable devices for isolation (without any caveats about earthing systems) which contains several SP devices (e.g. fuses).
Unusually for BS7671, it even gives an 'explanation' for this, saying that with TN-S and TN-C-S the supply neutral is deemed to be close to earth potential, and therefore is deemed to be safe enough not to require isolation. This is a bit ironic, given some people's concerns that the greatest hazard exists with a supply-side neutral fault with TN-C-S - in which situation that 'explanation'falls flat on its face!
Kind Regards, John.
P
Paul_C
And, as discussed a short while ago, considering the fact that even if the house might be arranged as TT, the supply neutral could be no different from the one provided if the house were connected for TN-C-S.
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