Two consumer units backfed

[mick b]

I have just come across a domestic installation that has two consumer units I was asked to wire extra sockets and do a board change as well. I found that the sockets of one board circuit are interconnected to a circuit from the other board, thus back feeding each other. This means that unless you isolate both boards or pull both relevant fuses then the whole installation remains live. I have wired my additional sockets to my own board , and explained to the client what the problem is. There is no way to find where these two circuits are interconnected without ripping up boards or going in loft and emptying it. And it's a possibility that it's been done more than once. Apart fron putting a warning notice for two sources of supply what am I meant to do. Mention of tearing the house apart was not well accepted.

 

[telectrix]

make sure you put it in writing and get customer to sign that he understands and does not want you to investigate.

 

[davesparks]

What you should do is advise the customer before you start work and if they don't agree to have it sorted then you should walk away and not do anything.

Why didn't you just move the offending circuit from one board to the other? Are these circuits ring finals? If so they may just be two legs mixed up.

 

[7029 dave]

^^^^ could be legs crossed or interconnection, needs testing to confirm.

 

[Deleted member 9648]

I have just come across a domestic installation that has two consumer units I was asked to wire extra sockets and do a board change as well. I found that the sockets of one board circuit are interconnected to a circuit from the other board, thus back feeding each other. This means that unless you isolate both boards or pull both relevant fuses then the whole installation remains live. I have wired my additional sockets to my own board , and explained to the client what the problem is. There is no way to find where these two circuits are interconnected without ripping up boards or going in loft and emptying it. And it's a possibility that it's been done more than once. Apart fron putting a warning notice for two sources of supply what am I meant to do. Mention of tearing the house apart was not well accepted.

Really cant see it being a major issue. Some basic testing and the source of the problem will be identified in less than an hour. Presumably your method of 'tearing the house apart' means you intended to find the problem visually rather than by testing.

 

[fall-apart-dave]

You could get some idea of what's what by doing a continuity check on all legs as Davesparks suggests, that will at least give a clue about what might be going on. In the event that does not show something simple like legs crossed, then there's still not a need to pull up floors straight away. Though it's unclear from your post what is actually happening... You say the whole installation is live unless fuses are pulled, could you clarify a little? is it one circuit or all circuits? Rings or radials?
If continuity checks at the board don't yield results, and it turns out one ring on one board is indeed connected to a ring from the other somewhere in the house, then before pulling boards up and tearing the loft apart, popping sockets off and disconnecting (trying to emulate something akin to the half split technique) will hopefully show where the offending cable is. It'd be tedious, likely not cheap for your time and boring doing continuity checks all day but it would go a long way to nailing the issue down and wouldn't need tearing a house to bits. Or do I have the wrong end of the stick here?

 

[telectrix]

Or do I have the wrong end of the stick here?

or the wrong end of the circuit?

 

[fall-apart-dave]

Or do I have the wrong end of the stick here?

or the wrong end of the circuit?

Unless it's a ring final... Then one end is as good as the other.

 

[telectrix]

unless the other end is the other RFC.

 

[joehat]

Currently then the circuits have to high of overload protection. Which is more dangerous


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[Octopus]

I have just come across a domestic installation that has two consumer units I was asked to wire extra sockets and do a board change as well. I found that the sockets of one board circuit are interconnected to a circuit from the other board, thus back feeding each other. This means that unless you isolate both boards or pull both relevant fuses then the whole installation remains live. I have wired my additional sockets to my own board , and explained to the client what the problem is. There is no way to find where these two circuits are interconnected without ripping up boards or going in loft and emptying it. And it's a possibility that it's been done more than once. Apart fron putting a warning notice for two sources of supply what am I meant to do. Mention of tearing the house apart was not well accepted.

Can you share with us the "notes" you put on your EIC concerning your initial findings?

 

[gnselectricals]

Bit of a poor show leaving the 2 interconnected circuits as they are and installing your stuff on anther board. Hardly 2 sources of supply either sounds like mixed up legs of 2 ring finals as mentioned earlier. Think I'd be on the phone to you if I was coming in behind you and it was left like that tbh


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[PEG]

If that was one of my "special" customers,they would get another spark in,after the last,and he would connect all three boards together...then,and only then,would i get the phone call...:icon11:

 

[mick b]

Why do I need a a report for an addition on my own board

 

[mick b]

Ok then what do you do

 

[Dave OCD]

Just identify the two 'common' circuits and if it isn't a wrongly connected RFC get all cables together in one board and one MCB, obviously making sure the rating of the OCPD is correct for the circuit.

 

[mick b]

That's fine but if you put all the sockets in the house on a 20 amp breaker then it's asking for trouble. Thanks for replying without a small amount of sarcasm

 

[davesparks]

Ok then what do you do

What type of circuits are they? Presumably they are rings?

 

[mick b]

One ring one radial

 

[davesparks]

Why do I need a a report for an addition on my own board

the installation fails to meet a basic level of safety and you have knowingly left it in that condition, and carried out work on the installation and so will end up facing some tough questions if something goes wrong.

 

[mick b]

Exactly. But who is going to find a fault that until I arrived , no one knew existed , and will they let me turn off all the sockets in the house, or pay me to put right something that never existed until I turned up, on a never ending goose chase around the house

 

[Dave OCD]

One ring one radial

Are you certain that there isn't an end of the ring at each board ?

 

[mick b]

Yes. One is a Wylex board which was added 30 yrs ago and the old one is a old mem with 4 fuses from original wiring .

 

[mick b]

Just another bodge job when extended

 

[Octopus]

Why do I need a a report for an addition on my own board

Comments on the installation! Surely you realise what you noticed is potentially very dangerous.

 

[davesparks]

Exactly. But who is going to find a fault that until I arrived , no one knew existed , and will they let me turn off all the sockets in the house, or pay me to put right something that never existed until I turned up, on a never ending goose chase around the house

Why would you turn off all of the sockets in the house? Why would there be a never ending goose chase? Only incompetent idiots attempting to find faults will go on never ending goose chases.

If they are not happy to have the fault rectified the walk away and don't do any work. Carrying out alterations/extension/addition to the installation knowing that a very dangerous fault exists is negligence on your part.

 

[davesparks]

Just another bodge job when extended

Yes, another bodge job by someone ignoring a dangerous existing fault and just fitting another board so that they can pretend the existing installation isn't there and take the easiest route to getting paid.