RCB ring main (upstairs) keeps tripping

[stevebl]

Hello,

Before I rip up all the carpet, I have a 30 amp RCB on an upstairs ring main and it keeps tripping off with a small bang. We had carpet fitted while I was away and I can only think that they have knocked something loose under the floor boards. It doesn't trip straight away, normally takes a min or two? I have replaced the breaker for a new one but it's the same story.

I have been round and unplugged everything on the offending ring main, but is there any way of checking plug sockets etc before I rip up all the carpets and floorboards to find a loose wire ? I have had a look inside each plug and the wires are all made off correctly.

Is it worth checking for continuity between RED/BLACK/EARTH back to the fuse box from each plug in turn in the hope of finding a loose connection?

What normally causes an RCB to blow after a min when nothing is plugged into the ring other than a short (should than not blow straight away?) or a loose wire ? (i.e. open cct).

All info greatly received.

enjoy,
Steve.

 

[Lectrician]

RCB??

Do you mean an RCD (normally protect more that one circuit), and MCB (the norm), or an RCBO (a combination of the previous 2).

What EXACTLY doest the breaker in question say on it??

If everything is unplugged, it does suggest a wiring a fault if it is still tripping. Nothing else on the circuit, such as a power shower, panel heater, spur to outside lights???

Looks like your carpet fitters may have used REALLY long nails

 

[stevebl]

Sorry, yes I meant RCD - its the one that supplies the upstairs ring main, all the other RCD's and the main breaker stay on OK.

I have unplugged everything from the ring, and all the plugs are off - there is one light switch in the porch which is spurred off the ring but it's still inside and everything looks OK.

Is it possible to buy a derive that checks plugs for continuity etc?

Does the fault (because it takes a couple of mins to blow) rather than straight away suddgest an open cct somewhere rather than a short?

Could I check each plug back to the consumer unit in the hope of finding an open somewhere. Save carpet etc................

cheers,
Steve.

 

[breezer]

since you said

all the other RCD's and the main breaker stay on OK.

may i suggest you read Lectricians initial reply to your question again

 

[ban-all-sheds]

Sorry, yes I meant RCD - its the one that supplies the upstairs ring main, all the other RCD's and the main breaker stay on OK.

Blimey - how many RCDs have you got? Most CUs have 1, or 2 if it's a TT installation. Not unusual to get a separate one for a shower circuit, but that's about it.

I have unplugged everything from the ring, and all the plugs are off -

Didn't know you could get plugs that had switches on them....

OK. I'm not trying to take the pi**, but it's going to be very difficult for you to explain problems, and understand advice, if you get basic terms like RCD/MCB and plug/socket confused.

there is one light switch in the porch which is spurred off the ring but it's still inside and everything looks OK.

Can you see electricity? Remove the bulb and switch off.

Is it possible to buy a derive that checks plugs for continuity etc?

If you mean device, yes - it's called a multimeter.

Does the fault (because it takes a couple of mins to blow) rather than straight away suddgest an open cct somewhere rather than a short?

From an electrical theory point of view, how could this work?

Could I check each plug back to the consumer unit in the hope of finding an open somewhere. Save carpet etc................

Plugs aren't connected to the CU. It's going to be very difficult for you to explain problems, and understand advice, if you get basic terms like plug/socket confused.

And what tests, with what equipment, do you think could be run, that wouldn't involve opening up the CU and attaching test leads to the conductors, terminal blocks and busbars in there? Doesn't sound to me like you'd be confident doing things like that....

 

[stevebl]

ban-all-sheds

Condratulations you are the biggest kn*b I have ever met.

 

[Canny]

One test you could do for continuity without opening the CU is to first switch off the power, remove one of the ring sockets and use your multimeter on its continuity test setting to check that both live cables (seperated once the socket is removed) test positively for continuity, then the same for both neutrals. Even if these tests are positive, it doesn't mean you don't have a problem though as there could be a nail through the live cable that is keeping the continuity but occasionally touching the earth cable thus tripping your RCD (perhaps with movement of a floorboard?). Such a scenario would assume that the cables have been laid in channels on top of the joists rather than fed through drilled holes in the joists as they should be.

If the test is negative though then you know for sure that there is a break somewhere in the ring, although unless it is something similar to the case I outlined above, I don't really see how that in itself would cause your problem.

Lastly, Breezer, Ban-all-sheds and lectrician all know far more than I do on this and so their advice and reccomendations in preference to anything I have said.

 

[plugwash]

Didn't know you could get plugs that had switches on them....

got one sitting in our garage. Don't think they make them anymore though.

 

[ban-all-sheds]

Lastly, Breezer, Ban-all-sheds and lectrician all know far more than I do on this and so their advice and reccomendations in preference to anything I have said.

But some of us have lost all interest in trying to help.

 

[breezer]

But some of us have lost all interest in trying to help.

yep, just because what we suggest is not what they want to hear does that mean we are wrong?

 

[Damocles]

Though you say that an RCD is tripping, everything else suggests it is a mcb which you are talking about. These two trip for different reasons, so we need to know precisely what it is. Does it have a test button on it as well as the switch? An rcd or rcbo(combined rcd and mcb) has a test button. a mcb does not.

An mcb might trip after a minute or so if you are pulling say 40A on a 32A circuit. Quite a big load. Does the meter whizz round? Or maybe an intermittent short, like a nail which moves when you walk over it.

An RCD will trip from a very small current which is escaping to earth. This could be a faulty appliance like a failing cooker ring, or even the electrical noise filter in a computer power supply. Again if it is on the limit (30mA), then it might trip a bit slowly.

 

[ban-all-sheds]

Damocles - please don't point out to him that it's vital that he doesn't get the terms MCB & RCD mixed up - he'll only get cross with you....

 

[Lectrician]

LOL

 

[kevplumb]

just a suggestion from a humble plumber why not put a glossary in the ref section

might save a lot of typing

and abuse

 

[ban-all-sheds]

just a suggestion from a humble plumber why not put a glossary in the ref section

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