Ring main MCB tripping, nothing plugged in.

[Joep1234]

Hello everyone,

Bit of a confusing one. I have a ring main on a 32A mcb. The MCB keeps tripping, sometimes the circuit will stay on for around half an hour then suddenly trip. This is still tripping with nothing plugged in. I have checked all sockets and made sure all connections are tight inside and sockets or switched spurs. Im not sure how the ring was wired as the cables inside the DB are the old colours yet all the cables i have checked that i can gain access too are the new colours so i believe there is more into it. I was just wondering if anyone has had any experience of this before and if so what i should be looking for as im stumped? Is it a break in the cable? but why would it stay live for 30 mins then suddenly trip?

 

[Richard Burns]

If your MCB is tripping after 30 minutes then it would appear to be an overload, as a simple check, look at the speed your meter is going round or the speed with which the little red light is flashing on the meter, then turn on the MCB and see if it is now very fast, then switch off and check again that it has slowed down. The MCB would also not be able to be reset immediately after tripping.
If this is the case then there is a significant fault on the circuit (or possibly something you do not realise is part of the socket circuit) and repeated attempts to reset the MCB will probably make the fault worse until it really shorts out.
If this is the case then getting some testing done would be a priority.
Just make sure your oven and immersion heater are not also on the same circuit as they are ones that could experience this sort of fault but normally only briefly until they fail completely.

 

[littlespark]

Not a direct short, or the MCB would never reset. Does the RCD work with the test button? It may also be faulty and not operating as it should.
New colours at CU but not in the back of any socket suggest a joint box somewhere or a socket you don't know about?
A cable may be getting squashed under a floorboard or in the back of a socket. Any with more than 2 sets of cables in a 25mm deep box?

There really is only one option for you; all together now... "Get an electrician in with the right test gear"

 

[PEG]

Hi,i did a post relating to this exact issue,a while ago. The client reported the fault,as you have described,and two different sparks,had tried and failed to find the cause.

To be honest,i had a bit of luck,but i'll take that,on top of proper technique. An IR test,had revealed nothing,and the fact it tripped the MCB more often in the afternoon,when it had warmed up a tad,led me to start a physical inspection,in the conservatory.

It was the third double socket outlet,which had two conductors pressed together hard enough,to thin the insulation...very hard to see,just the merest shadow of soot...

It could be cables bunched under a floor board,or over a hot pipe...you may need to get determined spark,in

 

[Wilko]

Had something similar - not so hard to find though. Immersion MCB would only stay on for "about half an hour". Cause found to be a big nail driven through the airing cupboard wall and the cable. The nail was not new, but had "recently" made sufficient contact for current to flow. Looks like it'd been cooking for a while before the MCB started to trip.

 

[willy fixit]

Is it raining?

 

[DPG]

Is it raining?

You need the weather forum

 

[Judd]

I remember having a earth fault blowing a 1361 cartridge fuse, a new fuse would last between 1 and 2 hours with no loads connected,
I/R readings bouncing all over the place leading me astray many times.
When I was ready to give up I noticed a heavy box of old books resting on a JB in the loft the knock outs hadnt been removed and was putting pressure on the cable, to naked eye the cable looked fine but was definitely the cause of the issue.
In your case the MCB tripping suggests a L-N fault, unless your RCD isn't operating correctly,

 

[The Ghost]

Anyone been using a steamer wallpaper stripper?