Faulty MCB. Problem isolating ring final circuit at CU with MCB

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maxeon

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I am planning to move a socket outlet. The CU is largely unlabelled so don't know which 32 MCB to switch off. There are 2 x 32a MCB. All other mcbs are for lights (6a) and a dedicated immersion (16a).
To isolate the circuit, I tried switching off the first of the two 32a mcb which isolated some of the sockets but not the one I need to move. So I switched the 2nd 32a mcb off too (so now all/both 32a MCBs off but some of sockets still live.
So I tested RCD and main switch which tripped all sockets other circuits off.
I am assuming there is no cross over of ring circuits and that the 2nd circuit is not picking up a live from elsewhere (heavens forbid) although I then switched off all MCBs on all circuits and the 2nd 32a circuit was still live.
Can I conclude that the 2nd MCB is faulty and so not switching off and needs replacing or is there any other possible cause?
I'm an amateur so please bear with me and this is my 1st post.
 
maxeon said:
I'm an amateur
Click to expand...

Do you have a two probe voltage tester.
First thing us to ensure that the MCBs are actually disconnecting when they are switched off.

Next you'll need to go done investigating yo find out which MCBs feed which sockets.
Put coloured stickers on the sockets so you don't get lost.

That should give you a starting point. If you can't cope with that simple stuff, then an electrician is what you need.
 
as above excellent advice. you need an electrician with the appropriate tools/test gear/ knowledge to sort this. you could fit your extra socket by isolating the whole installation, but there sounds like there's a nasty lurking away somewhere and to be honest, you won't have a clue how to find and rectify it. it could turn out to be fatal.
 
Taylortwocities said:
Do you have a two probe voltage tester.
First thing us to ensure that the MCBs are actually disconnecting when they are switched off.

Next you'll need to go done investigating yo find out which MCBs feed which sockets.
Put coloured stickers on the sockets so you don't get lost.

That should give you a starting point. If you can't cope with that simple stuff, then an electrician is what you need.
Click to expand...
 
I have a multimeter basic model but works ok. I am always very careful to check and double check that a circuit is actually isolated realising that RFCs can be cross linked by someone not paying attention to detail in there working practices. My double checking with instrement and a lamp before actually working on the circuit, lead me to find this problem. I appreciate I could simply flip the main switch and isolate the whole installation but I relaise that would not address the potentially serious problem. I suppose I was just wondering if a faulty MCB is the most likely cause bearing in mind I had switched off all other mcb including lighting/immersion circuits.
I had started to map out the mcbs to the outlets so as to get the CU properly labelled but then very quickly came across the issue. I think the next task is to check each/every MCB is actually switching off which may hopefully narrow down the problem.
 
buzzlightyear said:
it is possible the socket you are working on, is feed from one of the lighting circuits . and advise to get a local spark in.
Click to expand...
I am going to check that but the problem arose with all MCBs off so unless I have more than one faulty MCB I am thinking it might just be the one faulty 32a MCB. I really do hope a socket circuit is not picking up a live from a lighting circuit!
 
as said before, no doubting your abilities, but sometimes , maybe due to some bodger, a weird situation arises which is beyond your capabilities. might be time to call in an experienced spark with fault finding abilities to sort it.
 
Maxeon, apologise in advance if I've mis interpreted you problem ... without taking covers off consumer units or exposing live wires, can you not establish if the 32a Mcb is working by shutting every other mcb off. Identifying any electrical equipment that remains live then see what happens when you shut the final mcb off? If nothing happens then it's likely busted and it's time to call the spark. FYI, It is possible for sockets to be supplied from mcbs rated less than 32a.
 
maxeon said:
I have a multimeter basic model but works ok. I am always very careful to check and double check that a circuit is actually isolated realising that RFCs can be cross linked by someone not paying attention to detail in there working practices.
Click to expand...

You claim to be very careful in checking isolation, yet you only use a multimeter? This is contradictory, a standard multimeter is not suitable for use in safe isolation.
 
telectrix said:
but better than a neon screwdriver. :(
Click to expand...

Only Barely Tell.

Maxeon: Testing for Dead ( safe isolation ) Should only be carried out with an approved 2 pole tester, this should be tested to prove operation before testing for Dead and again afterwards. A Multimeter should Never be relied on to prove that a circuit is Safely Isolated, also it has to be said that you shouldn't be working on a circuit that has only had the single pole MCB isolated.
 
Specialist said:
Only Barely Tell.

Maxeon: Testing for Dead ( safe isolation ) Should only be carried out with an approved 2 pole tester, this should be tested to prove operation before testing for Dead and again afterwards. A Multimeter should Never be relied on to prove that a circuit is Safely Isolated, also it has to be said that you shouldn't be working on a circuit that has only had the single pole MCB isolated.
Click to expand...

I don't intend to work on the circuit with just the MCB off especially as my initial investigations trying to label all the circuits revealed ths issue!. Also I am not relying solely on the multimeter to check for isolation. I realise the limitations of the multimeter test (wrong setting- accidently switched off etc) rather than using the correct 'prover' instrement and using it correctly before, after to check its functioning correctly etc. I also know that someone before me could have bodged the circuits (even from when house was new!) and there could be polarity issues, wrong breakers etc. hence my care in checking and double checking and also realising when an issue is beyond my knowledge, understanding and capabilities and I appreciate the general advice to get a professional in which I may well end up doing, but as with all investigations in any field, you don't know how complicated the matter is until the investigation progresses. Sometimes the answer is simple and easy & safe for a competent DIYER to at least identify if not correct but I appreciate may be not so in this case.
 
Sorry but in your initial post, you said that you had turned off the 2 x 32a breakers to isolate the circuit. That would give you Single pole isolation, for correct Double pole isolation then you would have turned off the Main Switch or RCD.

Again I'd advise you, as others have. Call in a Qualified Electrician with the correct knowledge and test equipment to locate & rectify the situation safely.
 
Pete999 said:
Well for a start Dave it would prove whether the install has been interfered with or wired incorrectly, may seem expensive option, but better that than an unsafe install don't you think?
Click to expand...

I think it is already quite apparent that there is a problem, an eicr won't fix the problem it will just tell you that it's there. It will also still be just as unsafe.

The fault, or at least the symptom is already known, the next step should be to find the fault surely?
 
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