Single wall socket connected to two Mini Circuit Breakers.

Joined
18 Aug 2020
Messages
10
Reaction score
0
Country
United Kingdom
I live in a home built by property development group David Wilson that was built just over 30 years ago.

Today I decided I wanted to create a spur off a socket in my garage. Out of curiosity I decided to see which MCB it belonged to so shut off the switch labelled "downstairs sockets". This did not turn off the power to the socket. So i turned this switch back to on and switched of the MCB labelled "Upstairs sockets". Still didn't turn off the power. Turned off both MCBs and that shut off the power to the socket. This seems highly irregular. Why would a socket need two MCBs?

Do I need to get an electrician out to look at this? The plug has been providing power to my soldiering iron and workshop hoover for a decade but that still doesn't mean it's safe.

Thanks for any advice.

Dan.

P.s. this socket is supplied by two wires and think each go to their respective aforementioned MCBs. See picture attached.
 

Attachments

  • IMG20200818152422[1].jpg
    IMG20200818152422[1].jpg
    141.7 KB · Views: 289
Sponsored Links
I expect you will find that this little "feature" applies to many sockets in the house.
This is (usually) caused by someone connecting up the two (usually ring) circuits incorrectly and mixing up the final connections in the fuseboard
or
someone adding some wiring and connecting up the two circuits, somewhere.

It's not going to cause a fire, but it is dangerous for the unwary because ( as you have found out) turining off the downstairs sockets MCB should turn off that circuit.
-experienced electricians will always check that off really means off- but your average DIYer doesnt realise the dangers.

I really suggest that you get a competent electrician to investigate and resolve.
 
Do you have the same problem when trying to isolate other sockets in the house?
 
Do you have the same problem when trying to isolate other sockets in the house?

Yes, the upstairs and downstairs sockets are wired the same. With a dedicated wire (when i say wire I mean earth, neutral and live inside an insulated conduit) to each of the two MCBs.

I'm inclined to agree with Taylor and that this is an intended "feature" and not actually a mistake/problem. Can anyone explain the reason as to why to wire a house up like this to a DIYer like me?
 
Sponsored Links
Presumably then, each MCB in question has two wires at it, and someone has mixed them up, in the consumer unit.
 
I think you mis-read Taylor comment, The "feature" is ( almost certainly ) NOT intended and actually IS an error or mistake.

And also indicates a lack of testing by the 'Electrician' that originally fitted or change the wiring.

Mistakes will happen, but interconnected rings are not hard to detect and should easily have been picked up.
 
And also indicates a lack of testing by the 'Electrician' that originally fitted or change the wiring.

Mistakes will happen, but interconnected rings are not hard to detect and should easily have been picked up.
Struggling to think what test would have showed it up
 
I would think it's an order of operations issue.

If you do the ring continuity test and then immediately connect up the ring you have just tested the chances of such a screwup are minimal.

OTOH if you do all the disconnected tests in a batch, then only later connect up to the CU then the chances of such a screwup are much higher.
 
Presumably then, each MCB in question has two wires at it, and someone has mixed them up, in the consumer unit.

Correct but i'm not sure if this is a mistake as they've intentionally done it to every socket EXCEPT the single socket that comes directly off the consumer unit which i think must have been done by another electrician as it only uses one wire instead of the two and comes off a single MCB. It's how i'd have done it and how i'd expect it to be done. Edit: this is shown in pictures as the only gray wire running horizontally and leaving to the right of the frame.

See pictures attached. I've placed a green dot on the "upstairs" MCB and "downstairs" MCB. Also don't trust the labelling as this was done by a family friend over 5 years ago who isn't a qualified electrician. The dishwasher leaked and shorted a plug and he took the plug out, dried it and then returned it to the wall. I wasnt around for the repair. I can confirm the upstairs and downstairs lights switch off like you'd expect but thats it.
IMG20200818173212[1].jpg
IMG20200818152350[1].jpg
 
Last edited:
Struggling to think what test would have showed it up

Turn OFF all but one of the MCBs

Test the Live output terminal of each of the other MCBs relative to Neutral. They should all show no voltage ( other than some low induced voltages if using a high impedance voltmeter )

Turn that MCB to OFF

Turn the next MCB to ON
Test all other MCB output terminals

Repeat for all MCBs
 
Correct but i'm not sure if this is a mistake as they've intentionally done it to every socket EXCEPT the single socket that comes directly off the consumer unit
No. They have mistakenly done this to the two ring final circuits.
The single socket is not on the ring.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top