extractor fan wiring conventions

[helix]

when wiring in an extractor fan to switched and permanent live, I assume it doesn't really matter where the neutral is taken (either from from the light, or from the junction box)? Providing a permentant live, switched live and neutral are all fed to the 3 pole isolator then all is ok.

For the second live (i.e. the one not paired with a neutral), when going to the 3 pole isolator for the fan, is the neutral wire just not connected to anything and cut back?

 

[ban-all-sheds]

You don't have a "neutral" not paired with anything - you use 3-core + earth cable..

 

[ColJack]

spare cores should never just be cut back.. they should be terminated into a terminal block.. and depending on the circumstances may be earthed to remove coupled voltages from them..



common way if using ceiling roses and 3 plate wiring is to take the live, switched live and neutral from the light itself since all 3 should be present there..

 

[PrinceofDarkness]

Helix, that second paragraph of yours, makes no sense at all. The 3-pole isolator should be placed immediately before the final connection to the timer-fan.

So, why are you suggesting 'cutting back the neutral'?

 

[helix]

Please excuse my ignorance. 3 core + earth duly acquired. Thanks.

 

[ban-all-sheds]

Use the grey for neutral not the black.

 

[ericmark]

Use the grey for neutral not the black.

I would assume you are referring to Appendix 7 which does not stipulate what colours to use in an AC circuit where three core cable is used where two cores are line and one core in neutral except that id sleeves should be used.

However turning the page to colours with DC it does stipulate Brown or Grey to be used as line conductors which leaves Black to be used as mid point or neutral.

To use Black on DC and Grey on AC would be likely to cause mistakes so I would always use Black as neutral or mid point conductor in both AC and DC to avoid errors.

I see no hard and fast rules as to what to do when the colours are incorrect other than use sleeves and that green/yellow and cream are only used for earth and with exception of PEN conductor should not be numbered or sleeved.

 

[ColJack]

lets not start this debate again...

not set in stone so each to their own..

personally I would use black as neutral just as I always used blue as neutral in the old colours.. because that's what the old colour was and if in a mixed install it will match up..

imagine a situation..
new 3C+E in a ceiling rose with old red and black T+E..
common man would see 2 blacks and sticks them together..

some argue that grey is closer to blue...

 

[Spark123]

You can do it either way around as long as you sleeve with the appropriate colour i.e. sleeve the neutral blue and any other phase conductor other than the brown sleeve with brown.

 

[ban-all-sheds]

not set in stone so each to their own..

It's not set in stone, but black is now a phase colour, and the idea is to break the association between black and neutral.

personally I would use black as neutral just as I always used blue as neutral in the old colours.. because that's what the old colour was

Which is exactly why you should stop using black as the neutral.

new 3C+E in a ceiling rose with old red and black T+E..
common man would see 2 blacks and sticks them together..

He already does.

And your idea doesn't help because:

a) it panders to his ignorance

b) not all of the blacks at the rose are guaranteed to be neutrals anyway..

 

[ColJack]

all valid points with the exception of this one..

It's not set in stone, but black is now a phase colour, and the idea is to break the association between black and neutral.

grey is also a phase colour..
blue WAS a phase colour, but was accepted on the basis that flex neutrals are blue..
would you have used yellow as the neutral in old 3C+E?

black will always be associated with neutral as long as there exists an installation that still has red and black cables in it..

I think it much safer to keep black as neutral in mixed installations where the common man is likely to want to put their own stuff in..

"need to wire in my new fan.... hmmm... black must be neutral because it's neutral in the sockets I changed last week and that light in the living room that I changed last bank holiday.. "

in an ideal world they would produce twin brown and single blue cable to wire fans in, and 3 core SWA with brown, blue and earth rather than brown, black, grey.. but as far as I'm aware they don't..

 

[ban-all-sheds]

would you have used yellow as the neutral in old 3C+E?

Not the same issue - neither yellow nor blue were neutrals in cable other than flex.

Post harmonisation the world has changed - black is no longer neutral in any new cables, so people must stop automatically assuming it is, and the way to encourage that is for as many people as possible to stop using it as neutral, even with a blue sleeve.

black will always be associated with neutral as long as there exists an installation that still has red and black cables in it..

Which is exactly why you should stop using black as the neutral...

I think it much safer to keep black as neutral in mixed installations where the common man is likely to want to put their own stuff in..

I disagree - the more often people get bitten by their stupidity and laziness the more likely the population of common men is to get the message.

"need to wire in my new fan.... hmmm... black must be neutral because it's neutral in the sockets I changed last week and that light in the living room that I changed last bank holiday.. "

Serves him right for being stupid and lazy. The answer to the problem of people being too dumb to do things properly is not to dumb things down.

Deprecating the use of black as neutral isn't just my idea.

in an ideal world they would produce twin brown and single blue cable to wire fans in, and 3 core SWA with brown, blue and earth rather than brown, black, grey.. but as far as I'm aware they don't..

For exactly the same reason that they didn't make Red/Red/Black 3C+E or Red/Black/G-Y SWA.

 

[helix]

Interesting debate.

From my point of view (as a complete novice), it would be easier if the 3C+E followed the same colour convention as 2C+E but with the second live cable being brown with a white stripe for example.

Although I can see that for other uses of 3C+E (other than wiring a timed fan) this may not make sense!

 

[ericmark]

helix has asked for advice. As already stated as long as the earth wire is not used for anything else the other cables can be sleeved as required and any person preferences should be discussed else where. These arguments do not help helix in any way. Links to something like this

will be far more helpful.
I am sure BAS also has some wiring diagrams from what I remember better than mine.
What we must remember is these posts remain here for years. And some time in the future someone will read what we have said and take some pure electrician to task because he has read that he has got it wrong. So I feel where someone has voiced a personal preference it should shown as that and not some fixed ruling.
We have too many "Mark Coles" who want to read into regulations extras and seem to have a logic all of their own. This does not help the DIY man.

 

[ban-all-sheds]

Maybe the answer should be no neutral-less cables, i.e. no 3-core, or 3-core + earth, and that they are all either brown & blue, or brown, black, grey & blue, with or without a cpc as appropriate.