Bathroom fan wiring mystery

[hvendlor]

Trying to connect an timed extractor fan for the bathroom.

Fan requires Switched Live, Permanent live and Neutral.

Rigged up an FCU on the upstairs ring main, connected the fan to it. Fan comes on but it switches off when turned off(ie, timer not working). Checked permanent live, it's ok. Tried taking the permament live from somewhere else, same problem...

Checked the fuse in the FCU, it's fine. Did some experimenting and discovered that the only way we could get the fan to work correctly was to wire a plug to the SL and N and plug it into a wall socket, keeping the permanent live coming from the same place as it was before. This works and the fan keeps going after being switched off!

However, bizarrely, if you insert an extension socket between the fan cable with the plug on and the wall socket, the fan timer stops working again.

To be honest, we have no clue as to what's going on. Fan works, all the wiring is correct so why will the fan only work when plugged directly into a socket? It doesn't work when wired directly into the ring main, off an FCU or with an socket extension cable.

 

[holmslaw]

..

 

[garyo]

Sounds very strange - like some polarities are back to front and the extension cable has some kind of surge protecting diode in it that's not playing ball with the incorrect polarities.

Does the fan suck/blow in the right direction?

 

[hvendlor]

yep, fan going in the right direction. Really stumped on this one

 

[riveralt]

You haven't actually described how you have wired the FCU. You say that the FCU is off the ring final circuit. Is it now part of the RFC i.e. two lives and two neutrals and two earths in and out of the supply side terminals?

If this is the case have you then connected the three core and earth as follows. One conductor (brown say) to the supply side live (this is your permanent live). One conductor (say blue with brown sleeve) to your load live (your switched live) and the black conductor to the load neutral? Earth also connected on the load side.
And then replicated those conductor colours at the extractor fan.

 

[hvendlor]

yep, done exactly exactly you describe

FCU is part of the ring main (2 L, 2 N, 2 E's going in).

Took a 3 core cable from the FCU....fan comes on but doesn't over run when switched off.

 

[cumbriahandyman]

yep, done exactly exactly you describe

FCU is part of the ring main (2 L, 2 N, 2 E's going in).

Took a 3 core cable from the FCU....fan comes on but doesn't over run when switched off.

Can you adjust the timer? If so is it set to 0 instead of 5 - 15 - 20 - or however marked?

 

[yorkspark]

The fcu is isolating the neutral when turned off. This install needs rejigging to work as required.
You need to take the 3core to a new switch/pull switch and from load side of fcu take a twin and earth to new switch and connect as follows :-
Brown from twin to common of switch
Neutral connect to grey of 3 core with connector
Brown of 3 core to common
Black of 3 core to L1
At fan put brown to p live, black to sl and grey to neutral

Also please don't just connect brown of 3 core to supply side of fcu as suggested above as this will be fused at 32amp which will offer no protection for the 3 core and could be dangerous

 

[hvendlor]

Thanks for the suggestions, I'll try that. The fan is a CFD200T Manrose btw.

The thing is, the fcu is in the position where we want the fan switch to be(outside the bathroom door)....adding a new switch when the FCU already has a switch seems like one switch too many?

Is there anyway to make it work with only 1 switch?

 

[yorkspark]

Not by using the fcu as a switch like you plan to do, can you not lower the fcu and fit a switch in it's place or alternatively use mk grid and remove fcu and in it's place fit a 2 mod yoke fitted with a 13a fuse carrier ( change fuse to 3amp) and a 6amp switch like so :-
http://www.tlc-direct.co.uk/Images/Products/size_3/MKK4890.JPG
And
http://www.tlc-direct.co.uk/Images/Products/size_3/MKK4891.JPG
And
http://www.tlc-direct.co.uk/Images/Products/size_3/MKK3632.JPG
And not forgetting
http://www.tlc-direct.co.uk/Images/Products/size_3/MKK3702.JPG

 

[hvendlor]

At the moment the FCU is outside the bathroom door right next to the landing light switch.

Adding another switch on the wall there is just gonna look too much imo as the wall space is only small.

Would a 3 pole fan switch help me out in any way?

 

[holmslaw]

..

 

[sparkwright]

As mentioned, you need a single pole one way switch between the fcu and the fan.

The single pole one way switch can be wall mounted, probably outside the room, or a ceiling pull switch.

You would run a 2 core and earth cable from the fcu to the new switch, and run a 3 core and earth from here to the fan.

At the new switch connect the 2 core live and the 3 core permanent live (brown) to COM on the switch.

Connect the 3 core switched live (black perhaps, must be the same at the fan) to L1 on the switch.

Connect the 2 core neutral and the 3 core neutral (grey perhaps, must be the same at the fan) in a piece of connector block.

Connect all earths together.

Leave the fcu switched on, and use only the new switch for the fan.

On the 3 core cable, sleeve all live wires with brown sleeving, and sleeve the neutral with blue sleeving.

Use green and yellow sleeving over the bare earth wires.

No need for a 3 pole fan switch if the fcu is switched; it will isolate all 3 poles.

 

[hvendlor]

Thanks chaps, will try that tomorrow. Gonna make the landing switch a 2G and take a 2 core from the FCU across and then bring a 3 core down from the fan to the new switch as described.

 

[sparkwright]

Be sure not link the switches of the new 2 gang switch in any way as you have two completely different circuits there.