Found 1.5mm wire in my ring :(

[icarusbop]

Hello
I have found the sockets ring (in an out-building) is half wired with 1.5mm T+E instead of the correct 2.5mm. The cables are behind dry lined plasterboard, in front of the blockwork.
I am trying to rectify the situation with a minimal collateral damage as possible.
I have managed to replace two (short) lengths of the 1.5mm with 2.5mm (by drawing through the new cable with the old one).

There are now two lengths of 1.5mm cable, they go from twin-socket(0) across the wall around a corner and feed a single twin-socket(1), then move on to another twin-socket(2) around another corner. This length is approx 4.5m each leg. I have not been able to draw a new cable through this path and even if I did, I don't think it would meet clipping regulations.

As it is only destined to have a light load (table side lamp, phone charger etc.) instead of replacing these two cables (which is proving problematic), I am considering converting this twin-socket(1) to a fused spur, I would add a 13A fused spur box where the 2.5mm ends at twin-socket(0) and disconnect the return cable.
I do have a viable route to fit a 2.5mm cable to complete the ring from twin-socket(0) to twin-socket(2), the ring will end up smaller (not going all the way around the building), but it will be a ring leaving the spur as an outlier in the building.


Alternatively, does anyone have any other suggestion on how I can resolve this with minimal damage to the plasterwork?

 

[SUNRAY]

What size is the earth wire in your 1.5mm² cable?
What is the potential loading on the whole circuit?

IF the earth wire is 1.5mm² (only likely if it's a recent installation) you could possibly reduce the MCB to 16A but it would require a proper calculation as would be done for a new circuit.

 

[Taylortwocities]

How is the power to the outbuilding provided? From the house CU (value of the MCB please), or maybe from a house ring final via an FCU?

 

[ericmark]

Are you sure it is a ring final, and not a radial circuit?

 

[Murdochcat]

What’s the OCPD for the circuit?

 

[icarusbop]

What size is the earth wire in your 1.5mm² cable?
What is the potential loading on the whole circuit?

IF the earth wire is 1.5mm² (only likely if it's a recent installation) you could possibly reduce the MCB to 16A but it would require a proper calculation as would be done for a new circuit.

I don't know offhand but the wiring is probably as old as the extension which is approx 35 years (extension is to the outbuilding, the original outbuilding is as old as the main house). The cable is Red and Black. So I suspect the earth will not be 1.5mm (did it used to be 1.0mm?)

The suggested spur socket is going to be low load, table lamp, phone charger, that kind of thing.

 

[icarusbop]

How is the power to the outbuilding provided? From the house CU (value of the MCB please), or maybe from a house ring final via an FCU?

Power is provided via an armoured cable from the main building on a sperate (alongside the main house consumer unit)consumer unit located in the main house. This consumer unit is fed straight from the house feed (NOT via the main house consumer unit) via 100A connector blocks. The outhouse consumer unit has it's own ELCB/RCD (I don't know which offhand) with an MCB of 50A.
The outbuilding end also has a consumer unit with ELCB/RCD and a number of MCB's for various circuits.

Hopefully below will be clearer (if not let me know and I'll make a drawing)

Main house---OuthouseConsumer(in house, RCD/50A-MCB)<-------------[armoured cable]---------------------->Consumer(in outbuilding,RCD/various MCB)

 

[icarusbop]

Are you sure it is a ring final, and not a radial circuit?

I'm afraid so, I spent time removing all the sockets and tracing the cables with a meter. It is definitely a ring, I don't understand ring final though.

The outbuilding is as old as the main house and was extended around 35 years ago (before I lived there)
From the location of wires/sockets, it looks like the outbuilding has been wired up with a ring (and other circuits too) in the past.
When they added the extension to it, it looks like they broke the original ring and added the extension sockets to it but used the 1.5mm wire whilst doing so.
Perhaps the MCB was originally 16a (would this make the wiring OK?), and has since been changed for a 32A by someone who wasn't aware of the wiring sizes, but this is all speculation.

 

[icarusbop]

What’s the OCPD for the circuit?

It is a 32A MCB in a consumer unit, with a ELCB/RCD located in the outbuilding.

 

[AndyPRK]

ring and ring final are the same thing.

With a 50A supply to the building, you do need to do some corrective work.

 

[icarusbop]

I'm afraid so, I spent time removing all the sockets and tracing the cables with a meter. It is definitely a ring, I don't understand ring final though.

The outbuilding is as old as the main house and was extended around 35 years ago (before I lived there)
From the location of wires/sockets, it looks like the outbuilding has been wired up with a ring (and other circuits too) in the past.
When they added the extension to it, it looks like they broke the original ring and added the extension sockets to it but used the 1.5mm wire whilst doing so.
Perhaps the MCB was originally 16a (would this make the wiring OK?), and has since been changed for a 32A by someone who wasn't aware of the wiring sizes, but this is all speculation.

OK, ring final is the new name for a ring main.

 

[icarusbop]

ring and ring final are the same thing.

With a 50A supply to the building, you do need to do some corrective work.

Sorry - I posted my ring final comment before I saw this. Thanks.

Can you elaborate on what is the issue with the 50A supply please?

 

[AndyPRK]

I guess we were all hoping that your outbuilding was being supplied off a 16A MCB (or 13A FCU) from the house, and therefore it would protect your 1.5mm. But you tell us the upstream device is 50A, so can't use that excuse

 

[AndyPRK]

If your outbuilding CU has spare ways, and it's easy to get MCB's for it. Have a ponder if its worth having 2 radials instead. (break the ring).
16A MCB for your circuit which contains 1.5mm
20A MCB for 2.5mm circuit.

Only worth it, if you would have high loads off the 2.5mm connected sockets.

 

[SUNRAY]

Can you elaborate on what is the issue with the 50A supply please?

I expect nothing, as I understand it the feed to the extension building CU is 50A and there the ring has a 32A MCB, changing it to 16A is very likely to be your easiest option.
Andys idea is sound too.