One wall mounted light switch is causing the lighting circuit fuse on the consumer unit to blow. All other switches work fine. I noticed the switch was faulty so have changed it but the fuse still blows. Problems in changing the switch are that the wiring is old so the cables are black and red and the old switch isn't marked at all. So, I may have reversed he wiring but can't work out if this could be causing the problem to continue or even if I have the right solution. I've checked the other wiring as far as possible and it seems fine. The switch seems to be the key to it. Any info and advice is welcome.
switch blowing main fuse
- Thread starter Jimmymack
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So everything had been working fine, and without you changing/adding/fiddling with anything whatsoever on that circuit the fuse started blowing whenever you turned the light on?
What was the fault, and how did you notice it?
If they'd been blue and brown how would that have made a difference?
It can't - switches just make and break a connection between the two conductors, they work either way around.
'fraid not.
How have you checked it?
'fraid not.
Unless you have a multimeter and an understanding of how electrical circuits are wired you're going to struggle. Getting an electrician might be your best bet.
Like BAS states, the wiring of the switch should not be a factor, the fault lies elsewhere, just out of interest how did you wire it and is there an earth cable?
and has any work been carried out in the property of recent?
and has any work been carried out in the property of recent?
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So everything had been working fine, and without you changing/adding/fiddling with anything whatsoever on that circuit the fuse started blowing whenever you turned the light on?
That's exactly right.
I noticed the switch was faulty just after the fuse blew.
Thought so.
Looked at it for loose connections and water.
Thanks, you've confirmed my suspicions but I live in hope.
That's exactly right.
What was the fault, and how did you notice it?
I noticed the switch was faulty just after the fuse blew.
It can't - switches just make and break a connection between the two conductors, they work either way around.
Thought so.
How have you checked it?
Looked at it for loose connections and water.
Unless you have a multimeter and an understanding of how electrical circuits are wired you're going to struggle. Getting an electrician might be your best bet.[/quote]
Thanks, you've confirmed my suspicions but I live in hope.
I just wired it the same as the other using C at the top and L1 at the bottom. There is an earth cable which I just left alone. There's been work carried out to the property above but the main problems from there are usually to do with water leaking which was my first thought when it happened.
And is this circuit near where the water leak happened?
There you go - that's the cause. Someone's put a nail or screw through a cable in the floor, or disturbed some wiring. Can you find out what they did where to try and home in on possible locations?
Is the property purpose built flats, or a conversion?
It's a conversion. I suppose that could still be the cause, the place above was completely gutted and rebuilt but this was finished 5 month ago. Another thing has occurred to me which is that there is also an extractor built into the circuit which could have a fault or even got water in.
That means that your lighting circuit cables could be in notches in joists just waiting for someone to bang something into them.
If a cable has been nicked it can take a while for the problem to kick in.
One thing you could do which would be quick would be to disconnect the switch cable from the light and see if the problem stops.
1) It's unlikely that water could create a fault of low enough impedance to take out a fuse.
2) The fuse only blows when the you turn that one light on, so the problem lies in the switch cable or the light fitting.
Happy to hear it's sorted out.
So in what way was the extractor associated with the light switch?
I know it wasn't explicitly stated, but I think it was at least implied that the extractor was controlled by the same problem switch as the light fitting.
That's right, the extractor and the light were on the same circuit and the extractor was causing the problem. When you switched on the light you also switched on the extractor. Once that was taken out the problem was gone. I think he said there was a problem with the earth but beyond that I can't go.
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