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?

 

[mart spark]

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.

I agree that it's a poor design and have disconnected in the past the extra spur due to, more than one spur from the MCB seeming wrong due to it being non standard, but thinking about it afterwards i couldn't quite explain to myself why it was wrong, it. Only it being a poor design and non standard, but otherwise it wasn't unsafe. It reminds me telling a friend, when asked if it was wrong with doubling up the conducors on an undersized flex feeding a fixed item of equipment. I told him it was but then stumbled on explaining why it couldn't other than it being yee hawish and possibly the CPC being undersized. I suppose it's all food for thought.

 

[Rockingit]

I agree that it's a poor design and have disconnected in the past the extra spur due to, more than one spur from the MCB seeming wrong due to it being non standard, but thinking about it afterwards i couldn't quite explain to myself why it was wrong, it. Only it being a poor design and non standard, but otherwise it wasn't unsafe. It reminds me telling a friend, when asked if it was wrong with doubling up the conducors on an undersized flex feeding a fixed item of equipment. I told him it was but then stumbled on explaining why it couldn't other than it being yee hawish and possibly the CPC being undersized. I suppose it's all food for thought.

It's always good to remember that BS7671 is not a design guide; it's a set of rules and recommendations to inform a best-practice design decision and deviation is perfectly OK so long as it affords no less level of safety and stands up to scrutiny. It's the difference between an engineered solution and join-the-dots Ikea style.

 

[bigrich]

I'm glad I sparked a debate on this, seeing different perspectives. Seeing that snippet from BS7671 cements it for me, probably ok after all.

That is so long as my assumption that it's just a single socket is correct. I'll be checking it properly at the weekend to see what the situation is.

Thanks for the advice all.