Extractor Fan in a bathroom

[benthecowman]

Hi,

I'm planning the work for a bathroom and have reached the issue of the extractor fan and the wiring that goes with it.

The current setup is that there is a central light fitting with a loop in, loop out, a switch cable and a cable supplying L,N & E to an archaic looking extractor. There is also a single switched live running from the light switch to the fan.

I'd like to fit a new extractor with a timer again and have it so that it comes on with the light switch. I'm aware that there needs to be a triple pole isolator switch fitted in order to isolate the fan for maintenance without causing the lights to go off. It also seems that there needs to be a fused connection unit too though. I'm struggling though to work out how this FCU fits into the equation when they are all Double Pole not Triple Pole.

I'd hoped it would be a simple case of taking 3 core & E from the light fittings L, swL, N & E to a triple pole isolator pull cord and then from that to the fan. How is it possible to add in the DP FCU into this setup?

Any help grateful.

Thanks

 

[sparkwright]

The fused spur you mention is fitted as some fan manufacturers state the fan should be protected by a 3 amp fuse.

However, most installations I see don't have this, and the fan is protected by the 6 amp mcb/5 amp fuse at the consumer unit.

The important thing with the 3 amp fuse is that one 3 amp fuse needs to protect both the permanent live and the switched live of the fan.

The easiest way to achieve this is to fit a 3 amp fused spur that protects both the fan AND the light.

To do this, you could do the following;
Remove the twin + e and the single core that goes from the light to the fan, and discard.

Remove the feed in and feed out cables from the bathroom light, and re-route them to where the 3 amp spur will go. Outside the bathroom over the door is favourite. Connect both cables to the feed side of the 3 amp spur.

From the load side of the 3 amp spur, run a twin + e to the bathroom light. At the light connect this cable in the same way to two old feeds were connected. Leave the switch cable as it is.

Then run a 3 core + e from the light to the 3 pole pull cord. Brown is permanent live, black is switched live, grey is neutral.

From the 3 pole pull cord run another 3 core + e to the fan.

Connnect 3 pole fan switch and the fan.

Brown and blue sleeving is required to mark 3 core + e cable correctly. Use earth sleeving on all bare earths.

 

[benthecowman]

Thanks for such a clear and quick response Sparkwright.

I have a feeling that there might be an issue re-routing the loop in and out to above the door. The room is in a 1980s apartment which is dry lined concrete block wall and concrete slab ceiling and floors. There is an apartment above and below so there are no voids to access. As such I think I'd have to leave the loop in and outs as they are.

Am I ok then in planning to use the simpler method of taking the 3 core & E from the light fitting to the TP Isolator and then to the Fan? I mean in terms of Regs etc. I too have never come across a bathroom lighting circuit protected by a DP FCU.

Thanks again

 

[wingcoax]

If you did take the three core and E to the fan ,you could not have the timer function, as stated, it should have a switched live and a perm live.Edit; yes you could. i didn't read it right.

 

[sparkwright]

I suppose the next step is to discuss if fans really do need this 3 amp fuse. As I mentioned, it seems quite rare in 'real life' for people to actually fit these 3 amp fused spurs...

 

[benthecowman]

OK

Nice one Sparkwright.

 

[riveralt]

I suppose the next step is to discuss if fans really do need this 3 amp fuse. As I mentioned, it seems quite rare in 'real life' for people to actually fit these 3 amp fused spurs...

They are an absolute pain in the bum to retro fit - because you are invariably making the light and extractor fan separate from the household lighting circuit - not to mention the three pole isolator that is also normally required for timer units.

But, since most extractor fans, now come with a two year warranty, do you fit it as per MI and let them cover the warranty or do you fit as you see fit and you cover the warranty.

 

[EFLImpudence]

In view of the fact that the CPD is there to protect the cable what, exactly, is the purpose, reason or justification for the manufacturers of such a small device as an extractor fan dictating that we must fit a totally unnecessary item in a perfectly satisfactory circuit.

I have said before that if the manufacturers of these things think it essential then they should fit appropriate fusing inside their equipment but of course it's not.
However this is not really the point because what is going to happen to a, for example, 1A device that it needs 3A FUSE protection as 6A MCB won't do.

What other device, which comes without a flex fitted, demands a protection of, say for my example, three times its rating

This is not the same, as you know but I will state, as a cooker manufacturer stating it needs a 32A supply as this is a minimum need.

 

[ban-all-sheds]

What other device, which comes without a flex fitted, demands a protection of, say for my example, three times its rating.

Anything where the maker knows that he's selling such a pile of sh*te that he needs to do everything he can to be able to wriggle out of honouring any warranty...