RCD on 2 socket unit wont turn on...

[markyd1]

Have you replaced cable?

 

[JohnW2]

Yes ...But if that cable is too small it needs changing...

... and, strictly speaking, presumably changing to 4mm², if it is to continue to be protected by a 30A MCB.

Kind Regards, John

 

[winston1]

... and, strictly speaking, presumably changing to 4mm², if it is to continue to be protected by a 30A MCB.

Kind Regards, John

I disagree. It is a spur off a ring that just happens to connect to one end. A spur on a ring only need to be 2.5mm if it only feeds one double socket.

 

[JohnW2]

I disagree. It is a spur off a ring that just happens to connect to one end. A spur on a ring only need to be 2.5mm if it only feeds one double socket.

Thanks. I was hoping that someone would say something like that, since it affords me an opportunity to canvas opinion about an issue which arose during a recent discussion I had.

The fact that it is a spur from (the end of) a ring final is irrelevant. Method C 2.5mm² cable is always adequate for supplying just one double socket (even if it is not a 'spur' from a ring final), regardless of how high the rating of the upstream OPD (provided only that that OPD provides adequate fault protection), by virtue of the downstream 2 x 13A (or lower) fuses.

However, the question which arose during my discussion is the extent to which a designer can/should 'trust' people not to extend the circuit. In other words, how would people feel if I installed a "2.5mm² radial circuit" (not associated with any ring final), protected by a 32A (or even higher) MCB, which, currently, was feeding just one double socket?

Kind Regards, John

 

[EFLImpudence]

However, the question which arose during my discussion is the extent to which a designer can/should 'trust' people not to extend the circuit. In other words, how would people feel if I installed a "2.5mm² radial circuit" (not associated with any ring final), protected by a 32A (or even higher) MCB, which, currently, was feeding just one double socket?

I think it is a trick question like your previous post.

I would not, for a customer, put a 32A MCB on a 2.5mm² radial with a single double-socket so, I suppose, it would not arise without having to make other alterations.

So, the question really relates to any spur.
I am tempted to say that no consideration should be given to future incorrect extension - any more than considering people might surround the cable with thermal insulation - BUT if you think some/any consideration should be given then the only logical conclusion is that all such spurs should be wired in 4mm².
It would save a lot of regulation choices and confusion if this were the case.

However, that would also have to apply to spurs to a boiler, fan or cooker hood etc. unless any down-fusing were adjacent the supplying socket so I think I am back to giving no thought to future alterations by the unknowledgeable.

 

[Taylortwocities]

how would people feel if I installed a "2.5mm² radial circuit" (not associated with any ring final), protected by a 32A (or even higher) MCB, which, currently, was feeding just one double socket?

It's not something that most people would even think about. The standard 'go to' method would be a standard arrangement of either a 16A or 20A MCB on a 2.5mm² T&E. After all it's what we install for circuits such as an immersion heater.
I know what you thinking about: if its OK for a 2.5mm spur from a ring-serving 32A MCB then it should also be OK if there wasn't a ring there. But I'd code it C2 if I found it while doing an EICR.

 

[JohnW2]

I think it is a trick question like your previous post. I would not, for a customer, put a 32A MCB on a 2.5mm² radial with a single double-socket so, I suppose, it would not arise without having to make other alterations.

Exactly. That was the point ... the only really issue is the OPD ....

I am tempted to say that no consideration should be given to future incorrect extension - any more than considering people might surround the cable with thermal insulation ...

Indeed, as you imply, that is a very tempting view. However, what was being suggested about a 32A 2.5mm² radial (electrically fine when it was installed, since it was supplying just one double socket) is that the unnecessarily high OPD rating almost implied

Most of us probably have, on occasions, installed 'dedicated' circuits supplying only one socket using 2.5mm cable (or even 1.5mm² in the case of a single socket), but we will have used an 'appropriately-rated' OPD (up to 16A for 1.5mm², up to 25A for 2.5mm). However, as above, unnecessarily installing a higher-rated OPD than that would seem almost to imply that future extension of the circuit (into something non-compliant) was being contemplated. After all, one struggles to think of any other reason for installing an over-sized OPD (other than"it's the only one I had"!)

Kind Regards, John

 

[JohnW2]

It's not something that most people would even think about. The standard 'go to' method would be a standard arrangement of either a 16A or 20A MCB on a 2.5mm² T&E. After all it's what we install for circuits such as an immersion heater.

Exactly - but in those cases the OPD is appropriate to the cable.

I know what you thinking about: if its OK for a 2.5mm spur from a ring-serving 32A MCB then it should also be OK if there wasn't a ring there. But I'd code it C2 if I found it while doing an EICR.

That's exactly what was being said in the discussion I referred to - and, as you might imagine, some of the participants vociferously expressed the view that such a 'double standard' was irrational. One even asked if the C2 would go away if he connected both ends of a 6-inch length of cable to the MCB, in addition to the cable in question!!

I was primarily just a bystander in terms of that discussion, but when forced to offer an opinion, I confess that I took your view, for the reason I've just described to EFLI - that, whilst I don't think that a designer generally needs to consider possible future alterations, to unnecessarily protect such a circuit (a 'one socket radial') with a 32A MCB is almost 'begging for trouble'.

Kind Regards, John