RCD Problems

[jabberwocki]

I have a consumer unit with one RCD and 8 MCB. Have lived in the house about 3 years had had the occasiional nuisance trip. however this has now becoming much more frequent. symptoms are .
1. RCD trips but MCBs stay on.
2.. Need to turn off all MCB to rest RCD.
Ihave narrowed it down to one circuit(kitchen sockets) if I leave this MCB for the RCD does not trip. Despite uplugging all appliance cannot find any problem and still trips.

Just discovered this morning the test button on the RCD does not work. I have been rather lazy here as this is the 1st time I have tested it.

Just about to get a spark in but before I do does this sound like a faulty RCD. Anything else I can do before getting professional help.
Thanks

 

[PrenticeBoyofDerry]

If it's not a faulty appliance, could be a problem at your accessories on the circuit (socket outlets).
Could be a loose connection causing earth leakage, but if the test button don't function, I would wait to see what your electrician comes up with.
But you have done the logical steps and narrowed done the possible cause.

 

[ban-all-sheds]

1. RCD trips but MCBs stay on.

So a fault to earth somewhere.

2.. Need to turn off all MCB to rest RCD.

Perfectly normal.

Ihave narrowed it down to one circuit(kitchen sockets) if I leave this MCB for the RCD does not trip. Despite uplugging all appliance cannot find any problem and still trips.

So there's a leakage from line to earth - if it were neutral to earth it would still trip with the MCB off.

Just discovered this morning the test button on the RCD does not work. I have been rather lazy here as this is the 1st time I have tested it.

But the RCD does work - i.e. it is tripping. It may not be working properly though.

Just about to get a spark in but before I do does this sound like a faulty RCD.

It may be faulty, but that's not why it is tripping.

 

[jabberwocki]

Thanks for that. Yes looks as though I have done the logical tests and will get someone in. just as a matter of interest what should the spark do in terms of isolating the fault. Just so I have an idea what hes doing. thanks

 

[PrenticeBoyofDerry]

The electricain will do an inspection of your system, which will likely lead to some testing of the circuit and the RCD.

 

[bongos]

Most likely an insulation reisitance test on the faulty circuit(s). It sounds like you may have a L>E fault so this will identify if it is the case.

Probably an RCD test to confirm that is the RCD is functioning as it should, although if the test button isn't working then it might mean it's time for a replacement RCD.

 

[ColJack]

pint of virtual beer says it's a socket behind the washing machine got wet?

 

[Taylortwocities]

Pint of virtual cider says that the heating system is also on that circuit and the pump is leaking.

 

[LoveRocket]

2.. Need to turn off all MCB to rest RCD.

Perfectly normal.

 

[ban-all-sheds]

Yup - far from unknown for RCDs to behave like that.

 

[LoveRocket]

Yup - far from unknown for RCDs to behave like that.

Well every day is a school day, I have never known an RCCB to behave like that - you have to switch the RCCB itself fully off first, I've seen that, but never the downstream MCBs. Are some of them designed not to close "on load"? What is the mechanism that causes this?

 

[Taylortwocities]

I have seen that on several occassions.
Usually with a heavily loaded board. If you reset the RCD with the CBs on the RCD won't stay on.
Turn the CBs off, turn RCD on and then bring the CBs into operation one at a time and all is well.