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I live in the UK and recently had some building work done (replastering, new light fixtures, new switches, laminate flooring, etc). During the work the builders discovered a lot of dodgy electrical stuff and fixed things as they went. However, after the builders left we discovered a strange electrical problem.

Sometimes (but not every time) when we switch on the light in the kitchen it causes the power for the whole house to trip out. It doesn't happen every time but it does occur fairly often - I would say there is 50/50 chance.

The switch that causes the problem was not changed during the building work so I don't understand how it can affect it.

The builders have been back out and double checked the light switches and fixtures and say all looks ok. They say they cannot do anything about it because it doesn't happen every time. The only solution, they say, would be to re-wire everything all over again.

Here's a photo of my breaker:

enter image description here

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When the power to the whole house goes off is that tripping your main entry breaker? –  Michael Karas Jun 30 '13 at 20:35
    
Is the breaker that trips one with a ground fault detection capability? –  Michael Karas Jun 30 '13 at 20:36
    
Our fuse box has only 1 trip switch - I've seen other people's fuse box have several switches for different zones. I don't know if it has a ground fault detection capability. –  rf_wilson Jun 30 '13 at 20:38
    
So this trip switch is the main switch? You mention "fuse box". Are the individual circuits in your house protected by fuses as opposed to circuit breakers? –  Michael Karas Jun 30 '13 at 20:41
    
A photo of the fuse box (with the access door open) might help. A modern one look like this –  RedGrittyBrick Jun 30 '13 at 20:44
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2 Answers

up vote 5 down vote accepted

It sounds to me like the most plausible thing is that the builders installed some nails, screws or other fasteners to the wall or ceiling and punctured through some electrical wire causing an intermittent short circuit.

If the switching on of the kitchen light switch is what sets it off then you have already isolated it to a particular area of your house. It has to be a rather heavy duty short to cause it to trip your whole house breaker!!

Another thing to consider is that a fault of this type could very well be pretty dangerous. If the short was one that caused there to be live power present on the metal parts of any appliances or light fixtures this could be a very serious shock hazard.

There are tools that professionals can use to try to help find where shorts are located. Due to the potential serious safety issue involved with this I would strongly suggest that you get a professional electrician out to look into this problem as soon as possible. One reason for the urgency is that the short, where ever it is, may not be enough to always trip your whole house breaker but on the times where the breaker has not tripped the short could very well be generating a very hot connection which could lead a fire or burned out wiring. Take care of that call today.

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It's also a Residual-current device so it's possible that it is tripping with a small amount of current, provided it takes an alternate route. (picture added after you answered; just pinging you in case you want to include more information in your post) –  Brad Gilbert Jul 2 '13 at 5:19
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So I called out an electrician and he found the problem after a little trial and error. It turned out to be a fault with the light fitting itself. The light fitting holds 6 GU10 halogen bulbs. When he swapped it out for a standard light bulb the problem went away, we've been running like that for a week now.

It is strange because as I said above, the light fitting was touched during the building work. We're guessing that it must have somehow becomes damaged or dislodged indirectly. This weekend he is coming back to install a new fitting and we're assuming that will be ok too.

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Another update: it was not the light fitting as the new one had the same problem. It seems to be a problem with using too many GU10 LED bulbs in one fitting. If I install only three bulbs I have no problem. As soon as I add another, it trips out the power. So I am now back using 35W Halogens which work perfectly! –  rf_wilson Oct 15 '13 at 16:02
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