Double socket spurred off consumer unit?

[pete01]

Is that not what the OP says he is assuming in post #1?

Oh yeah I think so...

 

[ericmark]

It seems spurring off the ring in the CU is acceptable, and less likely to cause an overload as so near to origin.

 

[JohnW2]

It seems spurring off the ring in the CU is acceptable, and less likely to cause an overload as so near to origin.

I would think that's probably a confusing and potentially misleading statement for those who don't already 'understand' - since, in general, the closer a spur is to the origin of a ring, the greater is the theoretical risk of part of the ring cable (the 'shorter leg') being overloaded!

 

[ebee]

In practice, what determent to safety is there to having more than one "spur" of 2.5 T & E say, each having one twin socket max on the end of the radial?
Is there any potential danger having a 30/32A circuit running several radials each to its own twin socket, in comparison to having any such radial spur from either a socket on the ring or somewhere on the ring or direct from the fuseway?
I am not necessarily implying that such a set up would comply with the regs just merely has it added a potential danger that would not otherwise exist.

If with had a ring final with a number of sockets on the ring and one spur about half way and one spur at the fuseway and then after a time we removed the ring from the fuseway we would be left with one twin socket on a length of 2.5 T & E, has it now magically become more dangerous?
Some folks seem to think so!

 

[pete01]

Do you mean a 2.5mm cable from a 32 amp mcb feeding 1 x socket?

If so that's fine.

 

[ebee]

Do you mean a 2.5mm cable from a 32 amp mcb feeding 1 x socket?

If so that's fine.

Yes indeed all 2.5 T & E cables for example, whether ring or radial or spur and at the fuseway a 30A rewireable fuse or a 30A or 32A MCB.

 

[EFLImpudence]

Some mention should be made of the 13A fuse in the plug which is the over-current protection device in this situation.

 

[Jurassicspark]

Oh yeah I think so...

I know.

 

[JohnW2]

In practice, what determent to safety is there to having more than one "spur" of 2.5 T & E say, each having one twin socket max on the end of the radial?

None, provided that the 2.5mm² T+E is installed by Method C (CCC=27A), since the plug fuses would, at worst, provide 26A (2 x 13A) protection. That remains the case regardless of the upstream OPD - so Method C 2.5mm² T+E feeding one diouble socket would be fine if the upstream MCB was, say, 40A or 50A.

If the cable in not installed by method C then, unless there is an upstream OPD rated at 27 A or less, then it would, strictly speaking, probably be non-compliant. In relation to 32A ring finals (for which the cable of the ring is allowed to have a CCC as low as 20A), and 32A radials, Appendix 15 of BS 7671 does not make this point and could easily be read to imply (particularly for the ring final) that 2.5mm² T+E feeding a double socket is OK, regardless of installation method.

Kind Regards, John

 

[ebee]

None, provided that the 2.5mm² T+E is installed by Method C (CCC=27A), since the plug fuses would, at worst, provide 26A (2 x 13A) protection. That remains the case regardless of the upstream OPD - so Method C 2.5mm² T+E feeding one diouble socket would be fine if the upstream MCB was, say, 40A or 50A.

If the cable in not installed by method C then, unless there is an upstream OPD rated at 27 A or less, then it would, strictly speaking, probably be non-compliant. In relation to 32A ring finals (for which the cable of the ring is allowed to have a CCC as low as 20A), and 32A radials, Appendix 15 of BS 7671 does not make this point and could easily be read to imply (particularly for the ring final) that 2.5mm² T+E feeding a double socket is OK, regardless of installation method.

Kind Regards, John

The only thing that really needs to be taken into account is would the spur (radial) as installed be able to take the current in overload or earth fault or short circuit be able to take those currents, in almost most scenarios it would just in the same way that any ring or radial circuit would normally do so with its opd and cable conductor configuration . I must admit that if I saw a circuit such as a 32A MCB with 5 or 6 separate c!" ables each one terminating at a twin socket then initially I would be inclined to think "what" of course that would lead me to want to investigate what else had been done by the same or like minded person who might not know what they were doing (on the other hand it might just be an awkward git like me ).

I must admit it can be fun to see reactions to non standard circuits and quite amusing to see the reasoning some folk give for their points of view on them.
Some folk think I have a strange sense of humour - they might be right about that, I suppose that started some years ago before I was into electrics and I asked an electrician what was wrong with what we nowadays call a lollipop circuit (6.0 T & E feeding a small 2.5 ring final) and his answer was that the E conductor in the 6.0 portion was of a smaller current carrying capacity of the two 2.5s of the ring itself. Hmm! that started my unholy quest

 

[dal5band]

Ok - yes you can have a spur off a ring main. I didn't appreciate that a spur directly of the MCB is the same as a spur anywhere on the ring main.

 

[ebee]

Ok - yes you can have a spur off a ring main. I didn't appreciate that a spur directly of the MCB is the same as a spur anywhere on the ring main.

but what about 5 or 6 spurs from the fuseway whether the ring is present or disconnected?

 

[JohnW2]

but what about 5 or 6 spurs from the fuseway whether the ring is present or disconnected?

If the ring were 'disconnected' (or never had existed), then they wouldn't be spurs but, rather, multiple radials all originating at the 'fuseway' (interesting term ). As before, that would also be fine, if each of those radials supplied no more than one double socket and provided they were wired with Method C 2.5 mm² T+E - and all that more-or-less regardless of the rating of the upstream OPD.

 

[ebee]

If the ring were 'disconnected' (or never had existed), then they wouldn't be spurs but, rather, multiple radials all originating at the 'fuseway' (interesting term ). As before, that would also be fine, if each of those radials supplied no more than one double socket and provided they were wired with Method C 2.5 mm² T+E - and all that more-or-less regardless of the rating of the upstream OPD.

Agreed, but as i inferred myself, my first instinct would be shocked to see it, then if was the only noted occurrence I would see no problem as such.

Just like my suggestion of a two or three ring circuit being one circuit and being no more hazardous than as one larger ring, in fact rather better on volt drop and Zs considerations but yet again automatically "hey what!"

 

[pete01]

but what about 5 or 6 spurs from the fuseway whether the ring is present or disconnected?

2.5mm on a 32 amp then no, only 1 socket.

Edit....oh you mean all directly from the fuse? Suppose so if you can get 6 wires in there.