mcb tripping upstairs ring main

[Davepickard]

My upstairs ring main has been intermitently tripping now for about a week.

ive unplugged everything apart from a fridge/freezer and it still trips. It can take anything from 1 hour to trip up to a whole day before it trips.

So thinking it was the fridge/freezer I pat tested and it passed all ok so i have plugged that in downstairs for now via an extention lead, however the tripping has continued.

I have checked the backs of all the plug sockets for loose wires ect and seems to be no fault. I have also swaped over the upstairs and downstairs mcb's to rule out a faulty mcb.
The ring is running on 28a mcb and the fuse box is not an rcd.

Any serjestions on a possible fault?

 

[ColJack]

are we to assume that the "28a MCB" is a typo?

are you saying that an unloaded ring is overloading an MCB?

 

[sparkyspike]

The ring is running on 28a mcb

Any serjestions on a possible fault?

 

[Davepickard]

sorry yeah its a 32a
and ive checked the continuity and its better than downstairs

 

[securespark]

ive checked the continuity and its better than downstairs

What readings have you got?

 

[Davepickard]

i dont know my mate did it his an electriction he said it was low

 

[Spark123]

I'd do a 500v insulation resistance test as it sounds like something is shorting - make double sure everything is unplugged first!

 

[Davepickard]

If that was the problem would the ring still trip with nothing plugged in because it doesnt trip when nothing is connected.

 

[ColJack]

enough messing about now, we want pictures of the CU and the affected breaker before we continue to help diagnose..

 

[Davepickard]

Here are the pictures
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//media.diynot.com/122000_121127_11417_31831758_thumb.jpg
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3rd one from the left

 

[securespark]

Bit of a lo-res image, but they all look like MCB's.

As Spark 123 says, you need to disassociate all loads from this circuit and IR test it.

If a fault shows, split the ring and start trying to locate the faulty leg.

 

[Davepickard]

yeah they are mcb's.

lll do that next then.

Thanks

 

[ColJack]

3rd from the left?

would that be the one with grey tape on it? or the one next to it on it's right ( just making sure whether you're counting the main isolator..)

that's some mish-mash of mcb's you got there too..

we need a close up of the affected breaker, and in a larger size so that we can see it and see the writing on it..

( it might just be my dodgy eyes again, but that one with the grey tape on it looks like it might be an rcbo to me... which is a whole other kettle of fish.. )

what were the results when you swapped the breakers round for upstairs and downstairs? did the same breaker trip, or was it the one that you'd swapped the upstairs ting into?

 

[Davepickard]

//media.diynot.com/122000_121127_11421_34157641_thumb.jpg
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There the two we swtched round the one on the left is the problem ring.
When we switched them round the same ring kept on triping so its not a problem with the mcb itself.

I find it odd that this problem just suddenly started happening. What usaly is the underlying cause of these faults?

Should be able to do the 500v test at the weekend just to let you know.

 

[ColJack]

my educated guess would be a cable laying across a heating pipe upstairs under the floor..

it's eventually melted / worn out where it's in contact with the floor and when the pipe expands / someone walks on a nearby floorboard / turns on a tap that causes the pipe to move, then it trips..

when you IR test it, have someone walking about upstairs, turning taps on and off and turn the heating on..

even if you don't have radiators, it may still be a screw, nail or small charred rodent that is shorting out the wires so still have someone jumping about upstairs..