Spur sockets and ring mains

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Hello,

I am wondering how many spurs can you have off a ring socket without it being connected back to the ring? I have found a few in the house and I want to sort them with junction boxes so they can be joined to the existing ring but I would also like to know if this configuration is aright?

Thanks

James
 
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Unfused spurs can feed one accessory only.

Fused spurs can feed as many accessories as you like, as they will all be protected by the fuse in the spur feeding them, but you have to consider the limit on the load.
 
screenshot_364.jpg
 
Thanks. I am a little confused by the diagram though. Why would you use a 2.5mm cable for a single spur but then use 1.5mm for a fused spur? I thought all of the electrical sockets were 2.5mm minimum due to load?

I understand it's fused off at 13A and 1.5mm cable can handle about 15A but I thought 1.5mm was for lighting and not to be used for electrical sockets..

Thanks

James
 
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1.5mm² is good for approx 18amps - depending on the installation method.

1.5mm² is fine and is commonly used for loads that are limited by a 13amp fuse.
Take a look at the lead that comes from your kettle,or toaster. That will be a 13A load and the cable will almost certainly be "only" 1.5mm².

2.5mm² cable is required for an unfused spur, because you are able to put a double socket on the end, each capable of having a (fused) 13A load plugged in. 2.5mm² cable is rated at approx 27amp so 2x13 is within its capability.

Does that clear it up?
 
For clarity.

I am wondering how many spurs can you have off a ring socket
If, by spur, you correctly mean the branch circuit, then the answer could be more than one.
Some incorrectly call a Fused Connection Unit itself 'a spur'.

without it being connected back to the ring?
I take it you mean incorporated into the ring?
Obviously no point having a spur which is not connected.

I have found a few in the house and I want to sort them with junction boxes so they can be joined to the existing ring but I would also like to know if this configuration is aright?
Junction boxes raise other concerns regarding accessibility.
Can you not do what you want using the sockets themselves?
 
I am wondering how many spurs can you have off a ring socket without it being connected back to the ring?s
This question is not terriblly clear so to answer several possible interpretations.

Multiple accessories on the same unfused spur is a no-no. The regs previously allowed two single sockets on a spur but that changed a long time ago.

Multiple accessories on the same fused spur (starting from a FCU which may either be on the ring or fed by an unfused spur) is fine subject to loading considerations.

Multiple seperate unfused spurs starting from the same place each feeding a single accessory is not explicitly forbidden but is not shown in any of the examples either. Terminal capacity (most sockets are only rated to take three cables, so you may be violating manufacturers instructructions on the sockets) and ring balance would need to be considered in this case.

Thanks. I am a little confused by the diagram though. Why would you use a 2.5mm cable for a single spur but then use 1.5mm for a fused spur?
Rings and unfused spurs from rings are wired in cable with a rating of at least 20A. With normal T&E cable and no thermal insulation or grouping factors invovled that means 2.5mm cable (can be larger if thermal insulation is invovled or smaller if MICC is used).

Wiring downstream of a FCU is protected by the fuse so 1.5mm is fine by the regs.

Having said that I personally would use the same cable size for a fused spur as for the circuit feeding it on the grounds that things may get rearranged again in the future and just because a run is a fused spur right now doesn't mean it always will be.

I thought 1.5mm was for lighting and not to be used for electrical sockets..
You thought incorrectly.
 
The regs previously allowed two single sockets on a spur but that changed a long time ago.
Interestingly, AFAIAA the regs, per se, do not actually say anything about this. The 'one single or one double' socket (hence, by implication, not two single sockets) exists only in the 'informative guidance' of Appendix 15. I therefore suppose that it would/could be reg-compliant for a designer to decide (on the basis of knowledge etc.) that it was acceptable for two single sockets to be fed by a 2.5mm² unfused spur.

Kind Regards, John
 
The regs previously allowed two single sockets on a spur but that changed a long time ago.
Interestingly, AFAIAA the regs, per se, do not actually say anything about this. The 'one single or one double' socket (hence, by implication, not two single sockets) exists only in the 'informative guidance' of Appendix 15. I therefore suppose that it would/could be reg-compliant for a designer to decide (on the basis of knowledge etc.) that it was acceptable for two single sockets to be fed by a 2.5mm² unfused spur.

That's interesting.

On the basis that we may design anything as long as it is safe (and also within the constraints of the special requirements for ring circuits, which actually say NOTHING about spurs) do you consider that were the spur to be wired with larger conductors it would be acceptable to have more than two sockets?
 
That's interesting. ... On the basis that we may design anything as long as it is safe (and also within the constraints of the special requirements for ring circuits, which actually say NOTHING about spurs) ...
That would be my view - although how many would feel comfortable about their 'backsides' if they did that might be a different matter!
... do you consider that were the spur to be wired with larger conductors it would be acceptable to have more than two sockets?
In terms of protection of the spur cable, that would seemingly be acceptable.

However, there is obviously also the requirement to design a ring circuit in such a way as to make it "unlikely that the CCC of any of the cable will be exceeded for long periods" - and the more load one has connected to one point on a ring (if that point is close to one end of the ring), the more likely is that 'overloading' to occur. However, that's nothing specifically to do with spurs - to, hypothetically have, say, two double sockets spurred off a ring socket with 4mm ² cable is essentially 'no worse' than having three double sockets side-by-side on the ring.

Kind Regards, John
 
Interestingly, AFAIAA the regs, per se, do not actually say anything about this.

Plug mentioned that it used to be allowed, but not anymore:

From the 14th Ed, 1966:

A.40 ...............................Not more than two socket-outlets, or one twin socket outlet, or one stationary appliance, shall be fed from each non-fused spur.
 
Interestingly, AFAIAA the regs, per se, do not actually say anything about this.
Plug mentioned that it used to be allowed, but not anymore:
Yes, I understand that, but the current regs, per se, are totally silent on the issue, apart from recognising the existence of unfused spurs (433.1.204 starts off "... a ring final circuit, with or without unfused spurs, ...").

Hence, whilst it is true that current regs do not say that two single sockets on an unfused spur is 'allowed', it is equally true that nothing in the regs, per se, says that it is 'not allowed'. In fact, the regs, per se, say nothing about what is, and is not, allowed on on unfused spurs - we only have 'informative guidance', not regs, in relation to that.

Kind Regards, John
 
However, there is obviously also the requirement to design a ring circuit in such a way as to make it "unlikely that the CCC of any of the cable will be exceeded for long periods" - and the more load one has connected to one point on a ring (if that point is close to one end of the ring), the more likely is that 'overloading' to occur. However, that's nothing specifically to do with spurs - to, hypothetically have, say, two double sockets spurred off a ring socket with 4mm ² cable is essentially 'no worse' than having three double sockets side-by-side on the ring.
Theres an implied assumption in the whole design of a ring that large long duration loads will likely be "spread arround". If someone is using two 3KW electric fires or portable air conditioners in a domestic environment they are unlikely to put them in the same place*. The same assumption is seen in the facts that double sockets are not required to be tested at 26A and the fact that socket doublers are not required to be (and usually are not) fused.

Spurs (fused or unfused) can break this assumption by making the place where a load is plugged in different from the place it appears on the ring. Endorsing "fat spurs" would likely increase the temptation to create layouts that suffered badly from this problem.

I would assume the theory is that those who don't want to think too hard will follow the "informative" sections of the regs and more than likely end up with a reasonable result. Those who feel the need to ignore the informative sections can do so but they need to think harder about what they are doing.
 

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