Same Sockets from 2 different MCB's?

[egtrev]

Hi,

I recently moved into a rented house and decided to fit a 1 gang to 2 gang socket converter in the conservatory.
When attempting to isolate the sockets at the consumer unit I seemed to discover what I believe are issues.
The main one being I had to turn off 2 MCB's to isolate the conservatory sockets - if I left either of them on the sockets are still live.

Heres a partial layout of the consumer unit and their labels:

RCD > MCB "Downstairs Ring Circuit" | MCB "Kitchen Sockets" | MCB "Sockets"

If I turn off just "Kitchen Sockets" the conservatory (and Kitchen) are still live.
If I turn off just "Sockets" the conservatory (and Kitchen) are still live.
If I turn of both sockets then conservatory (and Kitchen) are off.

I ended just switching the main power off to fit the converter, so no issue but I want to make sure I'm correct in thinking that the same socket shouldn't be working off two different MCB's?

Thanks for any insight.

 

[EFLImpudence]

Correct.

The sockets are not wired correctly.
There will likely be two wires (ring) into each of the circuit breakers for these two circuits.
It would appear that one wire of each pair is in the wrong one.

Get the landlord to sort it as quickly as possibly.

 

[ericmark]

Likely some thing wrong, what size MCB's? I suppose one could you two 16A MCB's on a ring final, but would be unusual.

 

[egtrev]

what size MCB's?

Both 32A.

 

[ban-all-sheds]

I recently moved into a rented house and decided to fit a 1 gang to 2 gang socket converter in the conservatory.

Under the terms of your tenancy agreement are you allowed to do that?

 

[egtrev]

Under the terms of your tenancy agreement are you allowed to do that?

Yes.

 

[ban-all-sheds]

In that case

Get the landlord to sort it as quickly as possibly.

 

[ban-all-sheds]

Yes.

Did he plan to send anyone to check your work?

What is his general attitude to tenants carrying put electrical work?

I'm wondering if you have this dangerous mess because he lets any TDH fiddle with the wiring. He clearly doesn't think he should have the electrical installation inspected on a change of tenant.

 

[egtrev]

Did he plan to send anyone to check your work?

What is his general attitude to tenants carrying put electrical work?

I'm wondering if you have this dangerous mess because he lets any TDH fiddle with the wiring. He clearly doesn't think he should have the electrical installation inspected on a change of tenant.

Not that I know of.
I just told him what I wanted to do and asked if that was alright he said it was fine.

That's the thing - it was checked before I moved in, I have a copy of it done in December. That's one of the reasons I was questioning myself and wanted to make sure I wasn't wrong before I pursued it.

Thanks for the help guys

 

[JohnW2]

I suppose one could you two 16A MCB's on a ring final, but would be unusual.

Not just 'unusual' - surely dangerous and very non-compliant with regulations?

Kind Regards, John

 

[ban-all-sheds]

I just told him what I wanted to do and asked if that was alright he said it was fine.

Indeed.

The concern is to who else in the past has he said the same?

That's the thing - it was checked before I moved in, I have a copy of it done in December.

It could be that the guy who did it is a con-artist and/or unqualified and/or the landlords brother and/or should be reported.

 

[eveares]

Not just 'unusual' - surely dangerous and very non-compliant with regulations?

Indeed, It will likley violate some regulations in the 537.x.x.x region. You also have the uncertainty of what MCB will trip first due to the mechanical nature and the range of over current that will cause an MCB to operate. (i.e. 3X to 5X I2 for Type B MCB)

 

[JohnW2]

Indeed, It will likley violate some regulations in the 537.x.x.x region. You also have the uncertainty of what MCB will trip first due to the mechanical nature and the range of over current that will cause an MCB to operate. (i.e. 3X to 5X I2 for Type B MCB)

I suppose it doesn't really matter which one trips first, since both will have to trip before the circuit is de-energised and hence the fault/overload cleared.

Until the MCB getting the larger share of the fault current (which will depend upon where the fault is in the ring) trips, the amount of current flowing through the other one might be too low for a magnetic trip, so the actual time before the supply to the circuit was disconnected could presumably be anything up to double what one might expect if the whole current was flowing through, say, one B32, rather than one B16 at each end of the ring - and that might well also introduce a further non-compliance.

The main 'practical' dangers are probably those which relate to the fact that one has to open both MCBs to 'de-energise' the circuit.

Kind Regards, John

 

[ericmark]

Two things may have gone wrong, one is some one has in the past wired the conservatory as a figure of 8, when I was taught to inspect and test we were told to test for this, as it could cause an overload on one leg of the ring final, however it has been pointed out there is no regulation which says it should not be done, however if some one picks the wrong ring final then of course it is a real overload problem.

The second is some one, may have even been the guy doing the testing has swapped two wires in the consumer unit.

I did consider if simply switching off one MCB would cure the problem, however after consideration I think not, as it could form unfused spurs with more than one socket on it. As to swapping the two 32A MCB's for two 16A MCB's I can't see a problem, specially if a double 16A MCB was used so both would trip together.

If simply the two wires mixed in the consumer unit then not a real problem to put right, if a figure of 8 error then finding it may take some time, specially if a junction box was used.

So this raises the question should one test for figure of 8 as I was first taught? Clearly the fault needs tracing and correcting as one could draw 64 amp from the system and could be a serious overload. Hope you got permission to change socket in writing, and you need to inform the landlord in writing, text message would do, but health and safety rules must be in writing.

 

[ericmark]

Not just 'unusual' - surely dangerous and very non-compliant with regulations?

Kind Regards, John

Please state what regulation, can't think of one, as to danger with a single 32 amp MCB any large load near the origin of the ring can cause an overload, with two 16 amp MCB's linked neither leg can be over loaded so if anything safer. As to if not linked, with a three phase supply motor could single phase, but in a single phase supply only danger is if some one does not test for dead. As with fig 8 I think not following normal practice is wrong even if no rules broken, but as with fig of 8 can't see what rule is broken using two 16A linked MCB's. If some thing new only found in amendments could you say what it says, I only have the original BS7671:2008.