2 MCB's - 1 Socket 'Circuit'

Hi All,

Just moved into a 50's ex council house and need some advice/pointers.

Appear to have a modern CU (Siemens) with following MCBs (siemens 5sx2) etc (from left to right)

6A lighting circuit, 100A Switch, 20A (Unknown), 32A Sockets, 32A Sockets, RCD (ie whole house is rcd protected)

(Main and supplementary Earth bonding looks OK - TN-S)

ALL the sockets in the house seem to be fed via BOTH 32A MCB's.

ie to isolate any socket in the house requires that both 32A MCB be in the OFF position.

This just doesn't seem right to me....

Reply to
garion
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advice/pointers.

Sounds like someone has confused the start and finish of the upstairs and downstairs rings thus making a sort of figure of eight so I bet you'll find that one mcb has and upstairs 'start' and a downstairs 'finish' wheras the other mcb has an upstairs 'finish' and a downstairs 'start'. My house was like that when I bought it - relatively easy error for someone to make but potentially lethal.

(Bet the 20a is an immersion heater or maybe cooker or shower)

AWEM

Reply to
Andrew Mawson

Is there just one cable running from each MCB? If so, suggests that each end of a single ring has been wired into separate ways. Quite wrong, as you imply.

If there are two cables from each MCB that would suggest two separate ring circuits but wrongly wired at the CU so that each end of each goes into separate ways. Again quite wrong. As I'm sure you know a ring has and must have only one circuit protector.

Reply to
rrh

That's a very bizarre layout - main switch in between two MCBs, RCD at the other end. Have you looked inside to see how it's wired? Where do the tails go in? A photo (with cover removed) would probably be quite interesting, if you can put one up on the Web somewhere. Are you sure everything goes through the RCD?

At one time, when ring circuits were still a novelty, this was a fairly common practice. Two 15 A radials were converted into a ring, with no change to the fusing. Whether this was ever sanctioned by the IEE regs committee I don't know, but it did go on.

Too right! Sounds to me like an electrician from the Wild West may have visited and has replaced an old fusebox with an modern CU, attempting to replicate the previous layout as closely as possible, throwing in an RCD for good luck. I don't suppose for a moment that you got an Electrical Installation Certificate?

Reply to
Andy Wade

What is the cable core sizes from each MCB? How do you know the ccts are not radials in 4sqmm?

Jaymack

Reply to
John McLean

Sorry, just reread the posting, seems that you have a miswired ring if the two MCB's are required to isolate. I would recommend a PIR be done on your installation.. Jaymack

Reply to
John McLean

A 1950s house is the right age too. Is the wiring original rubber by any chance?

Yes it needs sorting, a 64A protected ring isnt a good idea. Simply putting the 2 tails into one 32A mcb is the simplest solution, but I'd want to look around and see if the ring was ok too, as someone has made a significant screwup there.

NT

Reply to
meow2222

Havent even attempted to remove the cover yet. (Dont know if I really want too!!)

Certainly seems to. If you turn the 100a switch off only lights go out,

if you turn RCD off everything goes off.

(Internet access bit difficult at the moment as still need to arrange ISP at home)

Electrical Installation Certificate??? hmmm

Exposed the wiring to the CU last night, looks like standard T&E, except lighting circuits which is single core live, and Live+E cable.

4 x 2.5mm2 cables (one runs about 1m to switch for outside light) other 3 disappear into ceiling.

Multiple live+e

1 x 4mm2 Not connected into CU.

Will have to investigate further I think....

Reply to
garion

Including the lights?

If so, it seems that it is supposed to be split load, with the RCD and main switch swapped round, so that the main switch controls everything and the RCD everything to its left. However, this would also require all the MCBs to swap sides. In any case, it all sounds quite a mess.

Christian.

Reply to
Christian McArdle

Oh dear - this is not a regular job...

Yes. If you don't feel confident to sort this by DIY, do as John McLean said and get an electrician in to PIR the whole premises. I would not be surprised to learn that there's a whole bunch of other horrors just waiting to be discovered.

Reply to
Andy Wade

It sounds like they have used a split load board but transposed the RCD and main switch. Then placed the lighting circuit on what should have been the RCD protected side, and all the other circuits on what ought to have been the non protected side. However the transposed RCD and switch partially alters the first cockup!

Reply to
John Rumm

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