WORRIED - two MCBs on ring main!

[jk5]

Hi guys

I was checking out my wiring earlier with a view to adding extractor fans to kitchen and bathroom and came across something I am sure is totally wrong.

My consumer unit has two MCBs, I had assumed I either had two rings, or more likely (2 bed room flat) two radial circuits.

However as far as I can tell ALL my sockets remain live if I switch off either mcb and they only go off if I switch off BOTH mcbs.

I am not a sparky but know more than your average pleb about residential electrics and I am pretty much certain that a ring main should be connected to only one MCB, and that by connecting to both it is not going to be safe - load would be split across both so wont trip when the cables rating is exceeded.

no idea how long its been like this but I've had the place for 4.5 years and its not burnt down yet.

Should I be worried?

Is there any reason to do it this way?

It was probably a bodge done when this was a council property can I get them to fix it - the blighters (substituted for the words I would really like to use)

Thanks for any replies.

 

[Taylortwocities]

I guess that each of the MCBs has two wires going into them? this means that you have two rings in the flat.

If so, it is likely that some monkey has switched the wires so that one leg of each goes into different mcbs. This happens when a consumer unit is changed or some upgrade work is done and the installer doesnt test his work!.

Get a qualified sparky to sort it out for you. Its dangerous like that.

 

[jk5]

I'll check and see how many cables are connected to each one tommorow, if it is the case that they have been cross connected how could I be certain, as if thats all it is I will just connect them up properly myself.

I am familiar with the theory of testing continuity of a ring main, but have never actually done it (or seen it done) it doesnt seem like a particularily difficult task.

I think the last people who did anything to my electrics was scottish gas when they fitted my boiler but would they not have done a safety check on the wiring before or after they fitted the boiler?

Any idea how much it would cost to get a sparky out to inspect and rectify (if it varies geographically I am in renfrewshire near paisley) would I have any comeback against whoever wired it up like that if I can identify who it was?

I have only ever had three people work on my electrics and I have a very strong suspicion that this may have happened when I got someone to add a few sockets into my kitchen, I am sure I remember him running new T&E from consumer unit, through a wall and to the first of the sockets.

I think he might have installed a radial but accidentally connected one end of the existing ring to the radials mcb. This would be the only time a mcb might have been added since I bought the place.

Will see what the sketch is tommorow.

 

[NoPoke]

You have already confirmed that something is wrong as both rcds have to be off to disconnect the circuit.

You can track it down a bit more precisely by operating each mcb in turn. As you suspect that the ring is wired into two breakers then you need to have all mcbs off and turn on each one individually. Only have one on at at time. This way you can establish which mcb or more likely mcbs feeds power to the circuit.

As it is possibly a ring main that has been mis-connected it is likely that another ring may also be misconnected. A count of the cables going to each mcb will give a good clue to the sparky as to what has happened.

A bit worrying that a radial may have been added incorrectly. That can be time consuming to track down. Still at least you know the sockets that the previous sparky worked on.

 

[rebuke]

It would sound plausible that the legs of ring mains are misconnected - if the rings are wired correctly elsewhere, and you have a multimeter (or even a battery and a bulb) you can determine which wires correspond to the same ring by disconnecting all the lives from the breakers and separating them, and then metering - you should have continuity between the two legs of the same ring.

If it's something crazy to do with a radial joining the ring, then this won't help as it will just get very confusing...

 

[Taylortwocities]

Aah yes,

This could also occur if , somehow, a connection has been made betwenn two separate rings.

Lets concentrate on mixed up legs in the consumer unit first and then go from there.