Spur off ring breaker

[bigrich]

Hi, looking for some advice on what I have seen at my mums house when I took the cover off the consumer unit.

32A breaker, labelled kitchen socket ring, 3 wires coming out of it. All look like 2.5mm2, two of them are same shade of brown so I suspect they will be the ring, and another to an unlabeled T&E. I know some cowboys did the kitchen, they did get involved with the electrics. I suspect this will go to an extra socket that was wanted nearby, haven't checked yet.

It looks wrong, personally I would have just put it on its own 20a breaker. But when I thought about it, how different is this setup to spuring off the ring elsewhere? You are still going to junction 3 cables together at some point, what is the extra risk of doing it at the breaker? It will make ring testing slightly more awkward, but otherwise?

 

[SJD]

There is nothing wrong with a spur at the origin (at the circuit breaker/RCBO).

However, since you have already looked inside (with the power off!), how about a photo so we can admire the quality of the workmanship!

 

[bigrich]

There is nothing wrong with a spur at the origin (at the circuit breaker/RCBO).

However, since you have already looked inside (with the power off!), how about a photo so we can admire the quality of the workmanship!

Wish I did take a photo, but I will be back there next week hopefully so will do it then.

Thanks for the advice!

 

[nicebutdim]

This extra conductor serves only one socket?

 

[Electreacle]

There is nothing wrong with a spur at the origin (at the circuit breaker/RCBO).

However, since you have already looked inside (with the power off!), how about a photo so we can admire the quality of the workmanship!

I thought this scenario was always ok but a colleague debated with me and said spurring from a breaker means that It’s now a 2.5mm radial off a 32amp breaker.

 

[Midwest]

But thats only the same for a single socket spurred off another socket on a RFC.

 

[littlespark]

What needs to be ascertained is how many sockets are being fed from this spur.

Taking one from anywhere on the ring is fine, but can only be one point. (A point being the maximum of a double socket)

If it turns out to be more than one, then is there a spare 16 or 20A breaker?

 

[Pretty Mouth]

I thought this scenario was always ok but a colleague debated with me and said spurring from a breaker means that It’s now a 2.5mm radial off a 32amp breaker.

Some circuits you can omit overload protection, or provide it further downstream. Design guide for rings is in appendix 15, but also have a read of 433, 434, and 435.

 

[davesparks]

I thought this scenario was always ok but a colleague debated with me and said spurring from a breaker means that It’s now a 2.5mm radial off a 32amp breaker.

It isn't a radial circuit, it is a ring circuit with a spur.
It would only be a radial circuit if the ring was disconnected from the OCPD and just the single cable connected.

 

[timhoward]

Appendix 17:

 

[brianmoooore]

a colleague debated with me

Is this colleague a qualified spark? Quite worrying if he is.

 

[Lucien Nunes]

spurring from a breaker means that It’s now a 2.5mm radial off a 32amp breaker.

The crux is that to qualify as a safe and compliant unfused spur, as mentioned above it must only serve one point, which is what prevents the cable being overloaded. It doesn't matter whether it comes from the MCB or some other point in the ring.

A 2.5mm² radial connected to a 32A MCB serving multiple points would indeed be non-compliant, as would an unfused spur from a ring serving multiple points, regardless of where it is connected.

 

[mart spark]

This thread reminds me of one that i read on here a while back debating if two seperate 2.5mm cables spurred off an MCB, that each fed a single socket, was permissible or not. Even though it doesn't seem right, with questions about about over filling the terminal etc and that only a maximum of one unfused spur per socket on an RFC, the problem regarding only one unfused spur related to the maximum current carrying capacity permitted for said said cable. Any thoughts?

 

[Rockingit]

I have always rationalised this mentally as whilst 2.5mm is only rated for 27A, if it's feeding only a double socket then I assume the overload protection argument is afforded downstream of origin by the two plug top fuses - being a maximum of 2 x 13A = 26A.

 

[Lucien Nunes]

two seperate 2.5mm cables spurred off an MCB, that each fed a single socket,

This is what I would call a pathological configuration that is specifically designed to be difficult to analyse in the terms set out in the regs.

An unfused spur on an RFC bypasses the convention Ib<In<Iz due to the downstream protection afforded by the load being a single BS1363 point (although, not full protection for cable with Iz=20A which are permissible on an RFC.) The defined format of the RFC and its spurs have been proven safe and effective in practice over 75 years of use.

The two-point centre-fed radial then tries to exploit the same idea in a situation that is not an RFC nor a defined standard circuit in BS7671. Therefore, while it should be no more or less safe electrically than two unfused spurs (although there are aspects of anticipated load to consider according to application) there are better ways of feeding two points that don't depend on that exemption adopted into the RFC.