Bathroom fan trips circuit breaker


Got a bathroom fan thats been there since the house was built (only 7 years ago). Its got a pull string switch as you go into the bathroom and the fan is on the opposite outside wall.
Been working fine until one day when I turned it on it tripped the circuit breaker. My circuit breaker is in the garage and has got a main switch as well as switches for upstairs/downstairs lights, upstairs/downstairs sockets etc - it tripped the upstairs lights one.
Tried again - tripped again.
So far, I've :-
1. Replaced the pull switch - still the same. 2. Replaced the entire extractor fan unit with a new one - still the same.
I'm afraid thats the limit of my electrical knowledge now. Anyone got any ideas ?
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Ah, the guy who used to do my MOT uses that method of fault finding. Very expensive.
OK, looks like the MCB is tripping rather than the RCD (the "main switch" in most modern consumer units), so it looks like you are dealling with a short between live and neutral. Does the MCB trip when you pull the pull-switch with the fan disconnected?
--

Graham.
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Yep. Its not the main big switch just the one for upstairs lights...
Not tried it with the fan disconnected...
One thing - there are 3 fans fitted in three of the bedrooms (running on this upstairs light circuits) fitted by me. They're all working fine, but could there be a possible wiring problem on one of them that is causing this???
If so, how do I know which one? (I guess I could start at the bedroom next to the bathroom!)
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paulfoel wrote:

Many bathroom fans were supplied with an external timer unit, so that they would remain running for a few minutes after the light was turned off. Newer ones tend to have the timer unit built-in.
If your existing fan unit didn't have two reds (one switched, one unswitched) and a black (plus a green/yellow) and it stayed on after the light went off, then you have an external timer unit.
The timer unit typically uses a capacitor/resistor series circuit to lower the input voltages to that used by the electronics. The resistor can overheat and damage the board with time, which can allow tracking, leakage current and circuit breaker trips.
It would be easiest to simply replace the timer unit, if that has failed. However, the wires going to the timer unit can be taken to a fan unit with built-in timer, instead.
--
Sue



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Sue,
Thanks for the info.
I have, however, tried a completely new unit...
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paulfoel wrote:

your system have a seperate timer unit and have you replaced that?
Modern bathroom fans tend to have an integral timer. Older ones often had a seperate timer unit - somewhere between switch and fan. Just a small plastic box, often with a clear cover and a screwdriver slot for setting the on time. With wires from it going to the switch and other wires going to the fan.
--
Sue





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No timer.
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Hi Just a thought but you don't say if the light is on the same pull switch as the fan (most are). If so check the light bulb sometimes the cheeper ones go short when they blow. Or you may have a problem with the light fitting not the fan.
HTH CJ
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Light switch is separate.
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OK. So the upstairs light circuit has got on it:-
- 3 combo fan/lights (3 bedrooms) - 2 normal lights (1 bedroom, 2 bathrooms) - 2 fans (2 bathrooms)
The one switch for one of the fans is causing the trip when its turned on...
However, is it possible that the fault could like elsewhere in the circuit ????
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paulfoel wrote:

There are many more explanations that are possible, but unlikely:
1) The total load is enough to trip the mcb. So try the switch with everything else on the circuit switched off.
2) The mcb is faulty and tripping on the fan motor start up - even with everything else off. So try swapping the mcb with a different one.
3) The fan switch is a two pole one and wired incorrectly. So it shorts the supply when pulled. Check the wiring.
4) The replacement fan is also faulty or wired incorrectly. So try it on a 3A fused mains lead.
5) You have been doing DIY and put a nail through the fixed wiring from switch to fan. So replace the cable.
6) Rats have eaten through the cable in the loft/ behind the wall. Replace the cable.
7) etc
So, try the following in sequence:
1) Disconnect the output cable from the switch and try the switch. If the mcb trips, the switch is faulty or wired incorrectly.
2) Reconnect the output cable to the switch and disconnect the wires from the fan, suitably insulating them in a choc box multi way connector. Operate the switch. If it trips, you have a cable fault - eg rats have bitten it.
3) Reconnect the fan and operate the switch. If it trips, swap the mcb.
--
Sue





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Sue, I must ask you this. You have started to do that cleaver =?UTF-8?B?UGFsaW5kcuKYu21l?= smiley thing again with your "from" header.It certainly makes your postings distinctive, but it was only when you stopped that I realised you were called Palindrome, and not Plindr me which sounds more like a request than a name.
Quite an enigma, are you going to leave it as it is?
--
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Graham wrote:

"Plindr" ??... O..K... as long as it doesn't involve Marmite..;)
I'm in the process of changing over to "Palindrome" but one or two machines in the workshop still have the old sig.
--
Sue




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Well I've been reading Sue's posts for as long as I can remember and that's the first time I've noticed the smiley in the header, but I like it!
Peter
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On Fri, 29 Jun 2007 22:25:48 GMT, "Peter Andrews"

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Regards,
Stuart.
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Still trips. Like I said this has all worked fine for years !!!!

Gulp! Sounds difficult...

This was working OK.

Hmm. Doubt it...

Nope.
LOL. Dont think so !

Yes. Someone else suggested that...

Whats a choc box multiway connector ????

How difficult is that? I've got a posh looking panel in the garage with switches on !!!!

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paulfoel wrote:

The scenario I'm thinking of is that the original fan went faulty - hence tripping the mcb. However, in putting in the new switch and new fan, you have introduced a new fault. Say by mis-wiring the double pole switch. It can be easy to do - the terminal layout on the new switch may not be identical to the terminal layout on the old one..

It is potentially lethal - as has been the things that you have already done, such as changing switches and mains fans. If you are at all unsure about what you are doing with any household electrics and feeling nervous - your instincts for self-preservation are kicking in with good reason. Listen to them. Do an evening course at your local college.. then you will be happy taking on anything.

Then you changed it. Are you absolutely positive that you wired the new switch correctly?

All of these possibilities are remote. But there has to be something wrong, somewhere.

Shame! That was one of the more realistic possibilities..

It has to be something. If the mcb is ok, the switch is ok, the fan is ok, there is nothing else switched on - then it has to be the wiring.

So, have you tried it?

http://www.maplin.co.uk/images/Full/l96_99ar.jpg
They are normally used to join wires /cables together *inside* equipment - where there *can't* be any pull on the wires and *can't* be any possibility of touching them. But they can also be used on the end of unused wires inside boxes, to insulate the wire end - or used to temporarily insulate the ends of free wires which aren't connected but may be going to be made live.

It isn't difficult but it has to be done with absolutely no mistakes, first time. The inside of the box will be live in places at all times.
Doing an evening course in domestic electrics makes sense. House electrics really isn't the thing to learn by trial and error. It only needs one teeny mistake to end up with someone dead or with the house on fire.
It sounds like you ought to get an electrician in, this time..
--
Sue
















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Hmmm. OK. thanks for the advice...
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