Double socket spurred off of Ring.

[CFTIS]

Ok so I'd like your opinions on this as I seem to be the minority on this.

I'm fairly newly qualified and obviously still learning everyday.

Electricians I work with and everywhere on the web says that spurring a double socket from another that is on a ring final circuit is fine, as long as it's just the one!

Ok so let's set the scene, one double socket spurred off of another via 1x 2.5 t and e, the source socket used is in a ring final circuit on a 32a mcb.

With my understanding 1 single 2.5mm t and e has a ccc of say 27a ref method c, so you could potentially plug 2x 3kw heaters into your spurred socket on full power and thus over load the cable but not the mcb causing potential danger ??

I know any danger is highly unlikely as you'd nearly never plug anything in to draw such a load but surely the potential to is enough for this not to be good practise ??

I must be missing something as everything and everyone I ask seems to say it's fine but surely you'd just extend the ring circuit or add a fused spur first before the additional socket ??

thoughts?

TIA.

 

[The Ghost]

Double socket is 13A

 

[Octopus]

Double socket is 13A

Single plug is 13A

 

[westward10]

They are type tested for 20A.

 

[The Ghost]

Ok so why do the manufacturers rate them at 13A on say the MK and Hager site?

 

[westward10]

They accept 13A, BS1363 plugs.

 

[The Ghost]

Ok I agree BS1363 four hours 14a 6a and so on. But somehow I doubt it really especially on cheaper sockets. Maybe MK and some others but In a commercial kitchen I was working in where they are running loads of 3kw items and for at least several hours a day, it is hard to whole heartedly advise that is OK. But then I suppose we are talking domestic. And anyway I think they should have had a single socket for each appliance.

 

[westward10]

I agree we used to work for one of the leading fast food outlets, chicken to be precise and they had multiple radial 13A points for individual appliances. You could have six sockets at one point covered by six circuits.

 

[Mark42]

Hi CFTIS
A bit of a digression, but the vagaries of RFCs are something which have annoyed me for decades. I personally think they are obsolete now that WWII is over and copper is plentiful, but it appears I'm in a minority here.
See this thread for details:
Can I join 2 radials to make a ring? - https://www.electriciansforums.co.uk/threads/can-i-join-2-radials-to-make-a-ring.123486/
I always enjoy splitting rings at the furthest point and converting them to 2 x 20A radials.
I believe rings are potentially dangerous after only a single (and common) point of failure (ring break). It's the same intuition that made you question the (regulation-acceptable) issue of daisy-chained spurs on a 32A breaker. Well done for obviously thinking it through.
We will now get replies saying that no one would ever plug multiple 13A loads into a single ring. Sure, that may be true, but if we assume it is always true, why then do we ever need to protect plug outlet circuits at 32A? That's my point. You can't have the argument both ways! (And I'm assuming good installation practice with no heavy fixed loads - eg immersion heaters - spurred off the ring.)
I hold that just because the regulations say that something may be done in a certain way does not ALWAYS make it the best, or even the right, way in every situation. And the converse is also true

 

[ipf]

Hi CFTIS
A bit of a digression, but the vagaries of RFCs are something which have annoyed me for decades. I personally think they are obsolete now that WWII is over and copper is plentiful, but it appears I'm in a minority here.

Each to his own...

 

[M-Ty]

I suspect this has been done many times before, but given that the CPC is smaller than the others in T&E, it may be more prone to damage. Therefore an O/C live conductor in a ring is less likely than an O/C earth in a radial, and equally unlikely to be noticed. It is then arguable whether the typical loading on a broken ring (effectively two radials) is more likely to cause danger by exceeding the rating of the cable than the lack of an earth on a radial past the broken part.

 

[marconi]

I have wondered why the mcb/rcbo makers have not yet made a specific breaker for the ring circuit which has 2 pairs of LNE terminals for the legs to be connected to and internal functionality to detect a break in any of the 3 rings and then trip.

 

[ian.]

Marconi that's a really good idea.

 

[Mark42]

... It is then arguable whether the typical loading on a broken ring (effectively two radials) is more likely to cause danger by exceeding the rating of the cable than the lack of an earth on a radial past the broken part.

That's a very good point which I admit I had never thought of before.
That rings have - by accident - what is effectively a high integrity earth is useful, but not useful enough to convince me to use them, unless protected at 20 or 25A (which I have occasionally done.)
Your point about an unnoticed broken earth applies of course to all types of circuit.

 

[Mark42]

I have wondered why the mcb/rcbo makers have not yet made a specific breaker for the ring circuit ...

Probably because there's little market outside the UK.
I once installed some RFCs, using UK sockets, in Asia, but could not get the local contractors to understand why they were wired like that. They were completely puzzled, and thought I was a madman.

 

[Lucien Nunes]

why then do we ever need to protect plug outlet circuits at 32A

Diversity & flexibility. Suppose you have three 2.4kW loads (this is an artifical case to illustrate, I accept it is stretching the point, but 3kW appliances are not as common as they used to be). You can plug them all in anywhere on a 32A circuit without further thought. With 2x 20A although you have 8A more available in total, you can't plug those three loads in anywhere without technically overloading one circuit.

The 32A vs. 20A debate is a separate consideration to the ring vs. radial debate, as you can have 32A radials which might be the best of both worlds.