Ring circuit fed by two MCBs?

A

askew70

Registered User
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I'm moving house soon and we've had a new consumer unit fitted to upgrade the existing unit. I was working out today which sockets are connected to which MCB. Simple process of plugging something into a socket and manually tripping each MCB in turn until I found the one that killed power to that socket.

At least, it was simple until I got to the plug sockets in the kitchen. No single MCB would kill power to the sockets, so I tried various combinations. Eventually I found the combination of two MCB's that had to be tripped to kill power. That also set off the house alarm so presumably it is fed from the same circuit(s?).

I'm confused by this, my simple understanding is that radial circuits and ring circuits are fed from a single MCB. Is it normal (and safe!) to have the same ring circuit (I'm guessing it must be a ring circuit in this case, by design or otherwise) fed by two MCB's? Perhaps the house alarm wiring is significant here too, but I'm not sure how.

If this is not a normal wiring setup then I'll have to get the electrician back out, so I'm keen to find out whether it sounds wrong. Thanks in advance for any info/help.
 
askew70 said:
I'm moving house soon and we've had a new consumer unit fitted to upgrade the existing unit. I was working out today which sockets are connected to which MCB. Simple process of plugging something into a socket and manually tripping each MCB in turn until I found the one that killed power to that socket.

At least, it was simple until I got to the plug sockets in the kitchen. No single MCB would kill power to the sockets, so I tried various combinations. Eventually I found the combination of two MCB's that had to be tripped to kill power. That also set off the house alarm so presumably it is fed from the same circuit(s?).

I'm confused by this, my simple understanding is that radial circuits and ring circuits are fed from a single MCB. Is it normal (and safe!) to have the same ring circuit (I'm guessing it must be a ring circuit in this case, by design or otherwise) fed by two MCB's? Perhaps the house alarm wiring is significant here too, but I'm not sure how.

If this is not a normal wiring setup then I'll have to get the electrician back out, so I'm keen to find out whether it sounds wrong. Thanks in advance for any info/help.
Click to expand...


ABSOLUTELY 100% wrong.
Get it sorted asap.
Should be simple enough to correct.
 
Thanks for the confirmation SparkRite, I'll be on to the electrician today to push to have this sorted out so it's helpful to know that I have a sound basis for insisting it be done.

I've since discovered that another circuit, a radial one this time by the looks of it, is fed by a 10A MCB. It seems to have nothing but (5) plug sockets on it and it's another thing that I would have expected the electrician to have spotted and identified to me as needing attention.

Further still, opening up some of the plug sockets revealed a right mess. I found what I initially thought was a plug socket on a ring circuit feeding two spurs, I've since realised that this plug socket is itself a spur so it's actually feeding three (and perhaps more) spurs. I'm not sure whether it's reasonable to expect the electrician to have spotted an issue at this level when upgrading the consumer unit though.
 
How did this pan out?

The sockets on the ring feeding the spurs could quite easily be missed as the "Electrician" ?? was only working on the CU, however, the sockets being protected by a 10A MCB should not have happened, along with 2 MCBs feeding the same ring.

When all is said and done the sparks should have thoroughly checked every circuit before signing off on the job.
 
The electrician I contracted to do this work had sub-contracted it to another guy. He sent the sub-contractor out to address the distribution board issues. The ring circuit now seems to be connected to just the one MCB, and he has replaced the 10A MCB with a 25A one (temporarily, apparently, until he sources a 20A one).

So, on the face of it those issues appear to have been sorted. However, there were some other pieces of work I'd paid to have done too, once of which was to install some outdoor sockets. He took a spur off an existing socket to run to the switched FCU. I'd pulled down a ceiling in preparation for insulated plasterboard to be installed, and this opened up access to the existing wiring runs to six plug sockets (on a radial circuit) in that area. He opted to spur off the only one of the six sockets that already had a spur, so that socket now has 4 (pairs of) wires to it. The ceiling has since been insulated, slabbed, and skimmed, so access to the other sockets is no longer available without chasing walls and perhaps the ceiling too.

The sub-contractor seems to have cut corners at every opportunity. This came through in the cable routes he chose elsewhere too (e.g. running house alarm cable vertically over the face of skirting board to an existing hole in the wall above for a radiator pipe instead of drilling a single hole under the skirting to run the cable in the void underneath), those I was willing to bite my tongue about as I was able to tidy them up myself with a few minutes effort - I should have got him back to sort them of course, but I'm under time pressure as other jobs are dependent on this work being completed. But running a 4th wire to a socket, presumably because it was the closest socket to the location for the new FCU, when there was relatively easy access available to 5 other safe/non-spurred sockets, goes beyond lazy, this guy either didn't know what he was doing or he simply didn't care, leaving me with absolutely zero confidence that the distribution board is anything other than a dangerous mess still.

So as things currently stand, I have a big question mark over the state, and safety, of the distribution board. Plus I have a mid-radial socket feeding two spurs which can't be sorted without a lot of effort. It's a mess, I've told the electrician that the sub-contractor isn't setting foot in the house again, someone can't demonstrate that level of unprofessionalism/ignorance one day and suddenly become trustworthy several days later, I simply wouldn't trust him to wire a plug.

The electrician himself is due out today to review the distribution board, he'll have his work cut out to reassure me that it is up to scratch though given the fiasco to date. He hasn't been paid yet, so that should motivate him, he is also the electrical contractor for another notable company that we are dealing with, so his reputation with them is at stake here too. However, even if the distribution board is fine, we are left with that socket feeding two spurs, he has suggested that he could put the radial circuit on an RCBO, I'm not sure that really offers any advantages although this radial lands on an MCB shared with another radial right now so I guess there is some side benefit in splitting the two out.

I'd be very interested to hear views on how dangerous it is to leave 4 (pairs of) wires to a single 2-gang socket like this, I gather that it is against the regulations, and is almost certainly outside of the spec for the socket too, but the alternative is a major headache. The farce continues.
 
askew70 said:
I'd be very interested to hear views on how dangerous it is to leave 4 (pairs of) wires to a single 2-gang socket like this, I gather that it is against the regulations, and is almost certainly outside of the spec for the socket too, but the alternative is a major headache. The farce continues.
Click to expand...


Getting 4 cables (of no less than 2.5mmsq each) safely terminated into a single terminal is pushing it a bit (although I have come across 6)! Also no more than one non fused spur is allowed per socket any more and a fused spur (13a) must be employed. Notwithstanding this, good practice would dictate that a joint box (JB) is safer than trying to force so many cables into a socket and back box.

I also fail to see the advantage of putting the spur/s on its own RCBO as presumably the circuit is already protected by an RCD at the CU board.

I would tend to agree with you that "short cuts" maybe the order of the day here. :-(
 
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