12 V Bathroom Fan - Weird - help needed.

[ajstars]

Hi,
Yesterday I fitted a 12V Manrose bathroom fan with the transformer in the loft. (Including a switched 3A fuse)
It is a simple affair - two wires to the fan from the transformer.
Positive and neutral from the light fitting, with a switched positive supply also from the light fitting.
I have wired the constant positive and negative through the 3A switched fuse.
All was working fine yesterday, you pull the light cord in the bathroom, the light and fan comes on. After the fans time out period it turned off.

Today however, with no lights on, the fan is constantly on!
I have checked the wiring, no shorts etc, but strangely the light on the transformer which is normally on when the fan is working is not illuminated, despite the fan working.

I have checked with a meter that the switched positive supply is off and that there is a constant positive 240v at the correct terminals and a neutral at the correct terminals on the transformer.

When I turn off the switched fuse though there is a very small voltage leak (I think it was about 6v) through the switched positive supply, but obviously the fan does not come on now because I have isolated the main feed.

What is going on - is this a fault with the transformer or with my wiring?
If it's my wiring then why was it working fine yesterday?

(I assume the switched fuse does not need to be earthed because the transformer has no earth - if it did I would have to run a seperate cable up to the fuse just as an earth)

Any help or suggestions appreciated.

Thanks,

 

[Lectrician]

Sounds like the transformer thats faulty IMO.

BUT, I am also a little concerned about the way you have wired your isolator (the fused spur). It is only isolating the permenent supply, not the switched supply?

 

[ajstars]

How would I go about protecting the switched supply?

The fused spur only had a total of four connections so I used these for the positive and negative constant supplies.

The house wiring is also on a circuit breaker - it was rewired just a few months back.

 

[Chivers7]

http://www.tlc-direct.co.uk/Main_In...Ultimate_Index/Ultimate_Fan_Switch/index.html

hope this helps

 

[ajstars]

Many thanks for that - so just out of interest would I still need the 3A fused spur anywhere or does that become redundant just relying on the house circuit breaker?

 

[Chivers7]

Unless the Fan manufacturer insists on one being fitted I wouldn't bother with one.

 

[Lectrician]

No one fits a fuse, it is simply not practical with timed fans.

Positive and negative is DC talk - We use AC - LIVE and NEUTRAL (or to be even pickier, PHASE and NEUTRAL).

 

[ajstars]

Tried fitting an energy saving lamp to the bathroom (with 12v manrose fan) the bulb glowed the fan came on without the switch being on, and then the fan transformer blew! (Manrose know of this problem with energy saving lamps)

Manrose sent me a new transformer circuit board which I fitted but still no fan! I have tested the Live, Switched Live and Neutral which are all ok, but no 12v from the Manrose Transformer!!

Is it possible that more than just the circuit board blew?

The transformer obvioulsy takes its power from the bathroom light which is switched (currently) by a single pole pull cord. That means that the live runs through a 3a fuse as recommended prior to entering the 3pole fan isolator switch whereby out comes the live, switched live and neutral. But that means when the light is turned on, the switched live is only protected by the lighting circuit fuse not a 3a fuse. Now, how would a double pole pull switch help me here as others suggest to fit?

Thanks.

 

[pjcomp]

No one fits a fuse, it is simply not practical with timed fans.

Positive and negative is DC talk - We use AC - LIVE and NEUTRAL (or to be even pickier, PHASE and NEUTRAL).

Or to be really, really 17th edition picky, LINE and neutral (but I can't get out of the PHASE habit)

PJ

 

[ajstars]

No one fits a fuse, it is simply not practical with timed fans.

Positive and negative is DC talk - We use AC - LIVE and NEUTRAL (or to be even pickier, PHASE and NEUTRAL).

Or to be really, really 17th edition picky, LINE and neutral (but I can't get out of the PHASE habit)

PJ

All very well but that does'nt help me in the slightest!

 

[electronicsuk]

Now, how would a double pole pull switch help me here as others suggest to fit?

It wouldn't do anything about the fact that your transformer/fan is still broken, but it would allow proper isolation of the L and SL to the fan along with fusing the circuit down.

One pole of the DP switch is used exclusively for the S/L to the bathroom light. You'd then need to bring a permanent L/N/E from the bathroom light/rose and into the supply side of a switched FCU (this would replace your existing 3-pole isolator), and take the load side L/N/E back to the DP switch. Use the remaining pole to switch L from the FCU load side, and run a 3C+E from the DP switch to the fan. N and E will have to be joined in a pair of terminal blocks at the switch, and the permanent L can share the same terminal in the DP switch as the incoming L from the FCU.

There may well be a drawing in the WIKI somewhere for this, as I'm pretty sure that the above, while making sense in my mind, may be hard to follow!

 

[ajstars]

Many thanks for that,
In essence although I can see that would work, surely it would be easier (considering my sparky wired it all up in the first place) to simply put a FCU on the switched live between the fan transformer and the DPpull switch?

That way the live is protected by a seperate 3a fuse, the neutral is running straight off the light (or pull cord) fitting and the switched live has it's own 3a fuse.

I know that will mean two fuses up in the loft, along with a 3 pole fan switch and the transformer, but it just seems like less wiring to me!

Is that a possibility or should I be calling Mr Sparky back?

Thanks again

 

[Risteard]

LIVE and NEUTRAL

That would be Live and Live then.

All Line conductors and the Neutral conductor are live conductors.

By convention, however, a PEN conductor is not considered to be a live conductor.

 

[ajstars]

Sparky it is then!

 

[electronicsuk]

That way the live is protected by a seperate 3a fuse, the neutral is running straight off the light (or pull cord) fitting and the switched live has it's own 3a fuse.

I think that's a bad idea, as should the fuse protecting the unswitched L ever decide to pop, I can imagine someone going to service the fan and not bothering to test the SL connection, which would of course still be live. A single point of isolation is much better than the very confusing setup you'd create by having two FCUs and a 3P isolator.