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Circuit breaker tripping intermittently.


 
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worcester4x4

from United Kingdom

Joined: 02 Apr 2006
Posts: 9
Location: Worcestershire,
United Kingdom

PostPosted: Fri Feb 20, 2009 2:48 pm Reply with quote

This started about an hour ago.

The CU trip switch controlling the lounge and dining room rings tripped with a loud bang. I heard it from two rooms away!

I attempted to reset it but there was an immediate visible flash from behind the breaker and it tripped out.

I turned off all power at the main switch, then reset the trip then turned the mains power back on, everything was fine. Five minutes later, bang - the trip cut out again. I unplugged everything from the rings and reset. I then plugged everything back in one by one with a time interval in between but everything remained fine. Five minutes after I plugged everything back in - bang again!

I repeated the procedure. It's now been 15 minutes, everything is plugged back in and all is OK. I'm waiting with bated breath now.

Can anyone offer any potential explanation for this sudden strange behaviour?

Pete
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rebuke

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Joined: 04 Nov 2008
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Location: Cambridgeshire,
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PostPosted: Fri Feb 20, 2009 2:53 pm Reply with quote

Is the breaker that's tripping an MCB (Miniature Circuit Breaker), or an RCD/RCCB (Residual Current Device / Circuit Breaker). The easiest way to tell if it's not labelled specifically is an RCD/RCCB should have a test button on it...
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worcester4x4

from United Kingdom

Joined: 02 Apr 2006
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Location: Worcestershire,
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PostPosted: Fri Feb 20, 2009 2:54 pm Reply with quote

Update:

It just tripped again for no reason that I can fathom.
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worcester4x4

from United Kingdom

Joined: 02 Apr 2006
Posts: 9
Location: Worcestershire,
United Kingdom

PostPosted: Fri Feb 20, 2009 2:54 pm Reply with quote

rebuke wrote:
Is the breaker that's tripping an MCB (Miniature Circuit Breaker), or an RCD/RCCB (Residual Current Device / Circuit Breaker). The easiest way to tell if it's not labelled specifically is an RCD/RCCB should have a test button on it...


It's an MCB
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worcester4x4

from United Kingdom

Joined: 02 Apr 2006
Posts: 9
Location: Worcestershire,
United Kingdom

PostPosted: Fri Feb 20, 2009 3:06 pm Reply with quote

Well, short and sweet but I found the problem.

The ferocity of the trip implied to me that it must be a major short so I wandered around sniffing the sockets! Sure enough one smelt 'ozoney / burnt rubbery'. I took the faceplate off and found that the insulation on one live wire was broken and it was 'leaking' to earth. Why it didn't blow immediately every time, and why this happened on a socket that's been in situ untouched for about five years I don't know.

Anyway, I'm confident that's that and sorry to clutter up the board with what turned out to be a mundane and obvious problem.

Pete
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Click-Sure

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PostPosted: Fri Feb 20, 2009 7:09 pm Reply with quote

Id hazard a guess that as the cable expands and contracts as a result of the heat that builds up as a result of loadng on the circuit it is moving close enough to create an arc between the live wire and the earthed back box, which causes a massive leak to earth resulting in your MCB tripping intermittantly.

The reason this has just occoured is probably because the cable has been rubbing up against the back box under load for some time, and has only recently work through enough to cause a short.

I bet if you'd left all of your appliances unplugged it wouldn't have happened.
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securespark

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PostPosted: Fri Feb 20, 2009 7:12 pm Reply with quote

Why?
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worcester4x4

from United Kingdom

Joined: 02 Apr 2006
Posts: 9
Location: Worcestershire,
United Kingdom

PostPosted: Fri Feb 20, 2009 7:18 pm Reply with quote

Click-Sure wrote:
Id hazard a guess that as the cable expands and contracts as a result of the heat that builds up as a result of loadng on the circuit it is moving close enough to create an arc between the live wire and the earthed back box, which causes a massive leak to earth resulting in your MCB tripping intermittantly.

The reason this has just occoured is probably because the cable has been rubbing up against the back box under load for some time, and has only recently work through enough to cause a short.

I bet if you'd left all of your appliances unplugged it wouldn't have happened.


I think you're probably correct.

Certainly had me guessing for an hour or so. All is well now though icon_smile.gif
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