# Solved: Mains trip switch problems



## jackdw (Jul 1, 2005)

Hi all. I'm in the UK and am in need of some help with the house electrics.

Recently got an old fuse-box replaced with about 12 separate circuit breakers. There is a main one on the end rated at 100A and then smaller ones to its right.

Problem: The 100A one keeps tripping itself off. Yesterday the electric oven, electric hob, 3 computers were on and it tripped when a power tool was started.
But before that it trips itself off overnight by itself when not much is turned on at all. And this morning it did it with just a few lights, one computer and possibly a kettle on.

There is high winds around my area and wondered if that was the cause, something to do with the electricity board.

Any ideas on this as it is REALLY annoying.....

Thanks
Jack


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## blues_harp28 (Jan 9, 2005)

High winds to one side for the moment..where are you in the Uk?
Was the fuse box installed by a qualified electrician?
Any tripping would be because the load on the electrical circuit was exceeded and as in the old days a fuse would blow but now the trip switch is thrown.
To trip overnight with little running may mean a faulty install or a damaged fuse box.
Get an electrician to take a look.


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## NICK G (Sep 11, 2006)

To trip the main, one of the paralleled smaller breakers would trip first if overloaded.
Faulty 100A breaker or faulty installation most likely. Have a pro check it out.


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## jackdw (Jul 1, 2005)

UK, Gloucestershire.
Fuse box was installed by a friend who is a qualified electrcian by trade.

It's been ok so far today, onyl power interuptions were in the local area, 1000 people so I wasn't alone that time.

If it does it again, should I get an electrician or shoudl I get one anyway?


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## NICK G (Sep 11, 2006)

If it does it again? I wouldn't trust it until checked out by a pro. Your whole house could go up in flames.


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## JohnWill (Oct 19, 2002)

FWIW, depending on the age of the main 100A breaker, it could just be defective. Circuit breakers have a finite lifetime, and are good for only so many cycles. Once it starts tripping without good reason, it's time to replace it.

Although most breakers can be a DIY job, the main breaker is tied directly to the incoming mains, so it's a job for the pros, and you'll have to disconnect the electrical service at the meter box to change it out.


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## jackdw (Jul 1, 2005)

Well the whole box was brand new about 12 months ago, upgrade from fuses.

It shouldn't have become faulty in 12 months should it? It very rarely got tripped before its recent little outburst.


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## n2gun (Mar 3, 2000)

like anything made, a bad one can slip out to be sold.


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## jackdw (Jul 1, 2005)

Yeh I guess. Best get back in touch with the electrician, see if it had a warranty or anything on it. Worse comes to worse, they're not that expensive are they..

Thanks for help everyone, will mark as solved.


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## JohnWill (Oct 19, 2002)

If it's only 12 months old, I'd be thinking other issues. You're SURE you don't have an overload with all the combined current draw?


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## jackdw (Jul 1, 2005)

Unless there's a fault somewhere in the house ring mains or something, no as it's been going off overnight.
Nothing is ever left on standby so the only things drawing power is two desktop PC's, centeral heating controls (timer etc) and a two routers, a switch and a wireless access point.

If it happens again I'll check what time during the night it goes off.

But over the last few days it's been fine, no problems whatsoever. Could damp air do it as the meter and fusebox is in a room that is being restored so isn't kept warm and damp air I guess gets in.


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## NICK G (Sep 11, 2006)

Once again, if the main trips, for any reason any time, something is wrong.
Weak breaker is hopefully the only problem. All other breakers would almost have to 
be fully loaded to draw 100A and trip main. Some sort of intermittent short in the line
from the main to the other breakers is hazardous. I've seen a simple break in the breaker
where the wires are screwed down to the breaker create so much heat that it eventually
separates and creates a heavy load, almost a short. Impossible to see and have to unscrew
the wires to feel it. I would replace the main breaker at the least. But that's me.
Good luck.


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## kiwiguy (Aug 17, 2003)

100 Amps equates to 23 kW, a cooker runs ~ 10 kW, a computer about 0.2kW.

That means it's tripping at about 25% of it's rated load. (UK has 230v)

Get it replaced.


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## JohnWill (Oct 19, 2002)

Well, he has more than just the cooker on it, and he did mention a "power tool".  Knowing what the actual load is would be useful here.


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## NICK G (Sep 11, 2006)

"But before that it trips itself off overnight by itself when not much is turned on at all."
Already been established that the overall load is not the problem if the above sentence
is accurate. It is so easy to check the load on any and all lines.
But then I have an AC 600A clamp-on meter.


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## JohnWill (Oct 19, 2002)

I keep my Sperry clamp-on handy for such diagnosis too.


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## NICK G (Sep 11, 2006)

Yeah, John, came in handy few days ago when I found outside compressor unit
fan motor over-amping considerably so replaced before it crapped out in the middle of
a hot humid night. It had tripped one breaker but fired back up and made no unusual noises.
Saved aggravation.:up:


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