1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Spur sockets and ring mains

Discussion in 'Electrics UK' started by morpheus83uk, 24 Feb 2015.

  1. morpheus83uk

    morpheus83uk

    Joined:
    4 Sep 2014
    Messages:
    516
    Thanks Received:
    5
    Location:
    Manchester
    Country:
    United Kingdom
    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
     
  2. Sponsored Links
  3. securespark

    securespark

    Joined:
    11 Jan 2004
    Messages:
    36,901
    Thanks Received:
    1,271
    Country:
    United Kingdom
    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.
     
  4. ban-all-sheds

    ban-all-sheds

    Joined:
    27 Aug 2003
    Messages:
    69,782
    Thanks Received:
    2,858
    Location:
    London
    Country:
    United Kingdom
  5. morpheus83uk

    morpheus83uk

    Joined:
    4 Sep 2014
    Messages:
    516
    Thanks Received:
    5
    Location:
    Manchester
    Country:
    United Kingdom
    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
     
  6. Taylortwocities

    Taylortwocities

    Joined:
    28 Jul 2006
    Messages:
    20,453
    Thanks Received:
    2,116
    Location:
    Oxfordshire
    Country:
    United Kingdom
    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?
     
  7. EFLImpudence

    EFLImpudence

    Joined:
    7 Jul 2010
    Messages:
    37,082
    Thanks Received:
    4,160
    Location:
    Retired to:
    Country:
    Portugal
    For clarity.

    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'.

    I take it you mean incorporated into the ring?
    Obviously no point having a spur which is not connected.

    Junction boxes raise other concerns regarding accessibility.
    Can you not do what you want using the sockets themselves?
     
  8. plugwash

    plugwash

    Joined:
    28 Mar 2004
    Messages:
    9,530
    Thanks Received:
    374
    Country:
    United Kingdom
    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.

    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.

    You thought incorrectly.
     
  9. JohnW2

    JohnW2

    Joined:
    28 Jan 2011
    Messages:
    48,157
    Thanks Received:
    3,142
    Location:
    Buckinghamshire
    Country:
    United Kingdom
    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
     
  10. Sponsored Links
  11. EFLImpudence

    EFLImpudence

    Joined:
    7 Jul 2010
    Messages:
    37,082
    Thanks Received:
    4,160
    Location:
    Retired to:
    Country:
    Portugal
    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?
     
  12. JohnW2

    JohnW2

    Joined:
    28 Jan 2011
    Messages:
    48,157
    Thanks Received:
    3,142
    Location:
    Buckinghamshire
    Country:
    United Kingdom
    That would be my view - although how many would feel comfortable about their 'backsides' if they did that might be a different matter!
    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
     
  13. securespark

    securespark

    Joined:
    11 Jan 2004
    Messages:
    36,901
    Thanks Received:
    1,271
    Country:
    United Kingdom
    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.
     
  14. JohnW2

    JohnW2

    Joined:
    28 Jan 2011
    Messages:
    48,157
    Thanks Received:
    3,142
    Location:
    Buckinghamshire
    Country:
    United Kingdom
    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
     
  15. EFLImpudence

    EFLImpudence

    Joined:
    7 Jul 2010
    Messages:
    37,082
    Thanks Received:
    4,160
    Location:
    Retired to:
    Country:
    Portugal
    Or you could say there used to be restrictions - but not any more. :)
     
  16. JohnW2

    JohnW2

    Joined:
    28 Jan 2011
    Messages:
    48,157
    Thanks Received:
    3,142
    Location:
    Buckinghamshire
    Country:
    United Kingdom
    Quite - there used to be restrictions, but now only silence (other than 'guidance').

    Kind Regards, John
     
  17. plugwash

    plugwash

    Joined:
    28 Mar 2004
    Messages:
    9,530
    Thanks Received:
    374
    Country:
    United Kingdom
    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.
     
Loading...

Share This Page