Extension of ring final circuit

raj_121 · Mar 30, 2021

Hi there all,

I have a property and I have noticed the following wiring (please see below) in one of the rooms in the house.

It looks like the ring circuit has been extended.
A single 2.5mm Twin + Earth cable (in red) is providing power from the consumer unit which feeds a chain of electrical sockets via a junction box which returns back to the junction box.

Every socket has two cables (feed in & feed out). To my understanding given that each socket has two cables (provided continuity is sound) the load would be shared between cables to ensure no one cable is overloaded.

However couldnt the single cable giving power from the consumer unit be overloaded or would that be fine given that the power returns back via the junction box?
Im guessing the single cable coming from the MCB with a 32a breaker could be overloaded right?

I know this is far from satifactory under regulations but my first concern is safety.

Soi disant · Mar 30, 2021

raj_121 said:
However couldnt the single cable giving power from the consumer unit be overloaded

Yes.

raj_121 said:
or would that be fine given that the power returns back via the junction box?

No.

raj_121 said:
Im guessing the single cable coming from the MCB with a 32a breaker could be overloaded right?

Yes - it needs to be rated to at least 32A, and 2.5mm² isn't, no matter how it's installed.

raj_121 said:
I know this is far from satifactory under regulations but my first concern is safety.

The circuit topology is what's known as a "lollipop", and whilst it is unusual, and can annoy electricians who have to test it, if you get the cable from the JB replaced with one rated ≥ 32A it won't be unsafe and won't contravene any regulations.

But if you're going to have that done, why not just make it a ring all the way?

What sort of JB is it? Where is it? Could a second one go there? How far is it from there to the first/last sockets? What's access to those cable routes like?

raj_121 · Mar 30, 2021

Soi disant said:
Yes.

No.

Yes - it needs to be rated to at least 32A, and 2.5mm² isn't, no matter how it's installed.

The circuit topology is what's known as a "lollipop", and whilst it is unusual, and can annoy electricians who have to test it, if you get the cable from the JB replaced with one rated ≥ 32A it won't be unsafe and won't contravene any regulations.

But if you're going to have that done, why not just make it a ring all the way?

What sort of JB is it? Where is it? Could a second one go there? How far is it from there to the first/last sockets? What's access to those cable routes like?

Interesting. I didn’t realise this was called a “lollipop”.

The cable from the consumer unit is under the floorboards upstairs.
The JB is one of those wago JBs with the 222 wago connector blocks.

I’m not sure if I can find the cable that returns back to the Consumer unit to make this ring circuit correct again.
I would otherwise use a junction box to connect to the last socket on this “lollipop” to rectify.

Thanks for your help.
I really appreciate your response.

Soi disant · Mar 31, 2021

raj_121 said:
I’m not sure if I can find the cable that returns back to the Consumer unit to make this ring circuit correct again.
I would otherwise use a junction box to connect to the last socket on this “lollipop” to rectify.

Well you really can't leave that 2.5mm² run from the CU to the JB on a 32A breaker.

telectrix · Mar 31, 2021

if the circuit is lightly loaded.i.e.no kitchen appliances or heaters, you could drop the MCB to a 20A, making sure the replacement id correct make ant type.

sinewove · Mar 31, 2021

raj_121 said:
Hi there all,

I have a property and I have noticed the following wiring (please see below) in one of the rooms in the house.

It looks like the ring circuit has been extended.
A single 2.5mm Twin + Earth cable (in red) is providing power from the consumer unit which feeds a chain of electrical sockets via a junction box which returns back to the junction box.

Every socket has two cables (feed in & feed out). To my understanding given that each socket has two cables (provided continuity is sound) the load would be shared between cables to ensure no one cable is overloaded.

However couldnt the single cable giving power from the consumer unit be overloaded or would that be fine given that the power returns back via the junction box?
Im guessing the single cable coming from the MCB with a 32a breaker could be overloaded right?

I know this is far from satifactory under regulations but my first concern is safety.

No,if I understand the your layout any ring final cct starts at the consumer unit, connects into various sockets
then returns to the cu,so 2 cables in the mcb.Sounds like you have a daisy chain of sockets without a return so chance of overloading the cable.A solution could be to fit a fused spur at the start of the chain,remembering no more than 13A could be drawn on the chain of sockets.Volt drop and other factors
would also have to be considered.
Regards,S

pc1966 · Mar 31, 2021

If your red "power from the consumer unit" cable is 2.5mm then the MCB should be 20A, as 32A is too much for overload protection.

If it was 4mm (without much thermal insulation) or 6mm (as commonly for cooker feeds) then you could get away with a 32A MCB no problems.

Grant1987 · Mar 31, 2021

pc1966 said:
If your red "power from the consumer unit" cable is 2.5mm then the MCB should be 20A, as 32A is too much for overload protection.

If it was 4mm (without much thermal insulation) or 6mm (as commonly for cooker feeds) then you could get away with a 32A MCB no problems.

I might be mis interpreting this but as far as I’m aware you are allowed to (spur off) from a ring final circuit mcb 32A at mcb providing it powers one socket outlet. The regs do show a nice picture diagram of this. It is no different to spurring off a socket outlet connected directly to the ring final. Hope this helps

Soi disant · Apr 1, 2021

sinewove said:
No,if I understand the your layout any ring final cct starts at the consumer unit, connects into various sockets
then returns to the cu,so 2 cables in the mcb.Sounds like you have a daisy chain of sockets without a return

I took it that the red cable is a 3rd one from the breaker....

Grant1987 said:
I might be mis interpreting this but as far as I’m aware you are allowed to (spur off) from a ring final circuit mcb 32A at mcb providing it powers one socket outlet. The regs do show a nice picture diagram of this. It is no different to spurring off a socket outlet connected directly to the ring final. Hope this helps

It's very different in that none of the current for the "spur" flows in the ring final, so none of the concerns about overloading a section of that would apply.