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I`ve been thinking

ebee
OK the title might startle some who know me.

Ring Final rules.

What is the intention behind the rule "no more spurs than points on the ring".

I think most of us who have run rings would almost exclusively put every point on a ring and no spurs at all.

Spurs are then usually just additions.

One spur max per point.

One spur allowed at origin.

If I saw a ring with say 12 points on ring and one ring per point and say 1 point at origin that would be 12 on ring and 13 spurs that would not worry me.

In fact if I saw say 5 points at origin it would not worry me either.

If I saw 12 on ring each with one spur then 5 spurs at origin then 11 spurs on joints between points woul I worry?

No I would not although this "golden rule" would have been well and truly broken.

I think the rule intention was purely good housekeeping to keep us all on the straight and narrow.

In fact some on here have mentionded a ring in a loft with junction boxes dropped dow to spurs. Therefore all spurs and not on ring.

Note I did not pick the number of 12 points on ring for any reason, I could have picked 5 or 50 or 5000.
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    But not a safe assumption when dealing with existing as earlier rules permitted two (single) sockets on the same spur - so two cables at one socket could still legitimately be a spur (never mind later instances with less legitimacy but just as much actuality).

      - Andy.

     




    Having just dusted off an old copy of the 14th Edition I.E.E. Regs dated 1976 in Reg. A.40 it requires that non fused spurs shall have a current rating of not less than that of the conductors forming the ring.


    Z.

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    Which would be 2.5 T & E ?
  • Former Community Member
    0 Former Community Member
    I'm just trying to recall which of the housebuilders back in the 80's used to run a ring around for upstairs then spur off at the "ring" sockets for all the downstairs points - at pretty well every upstairs socket you'd find 3 x 2.5mm2 T&E


    Regards


    OMS
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    ebee:

    Which would be 2.5 T & E ?




    I always assumed 2.5mm2, but "a current rating of not less than that of the conductors forming the ring" implies 5.0mm2 does it not?


    Z..

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    No, I think the intention is always that the spurs are wired in the same stuff as the ring, namely 2.5mm. IF you had 4mm radials the 2 socket limit would make no sense.


    In any case the rating of 2.5mmsq is 27A for surface wired or in plaster - which would have been the options when it was being dreamt up. Dont forget that part L and all this thermal stuff ony go t going after the 1984 revisions to the building regs - because until you have central heating the indoor and outdoor temps in all rooms without a fireplace are not so different.
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    Zoomup:




    ebee:

    Which would be 2.5 T & E ?




    I always assumed 2.5mm2, but "a current rating of not less than that of the conductors forming the ring" implies 5.0mm2 does it not?


     


     




     

    Not I`d say Zoom,


    Yes you could read that either way I admit. But you`d never say "I wired a ring in 5.0mm" would you? you`d say that it is wired  2.5mm even though it is fed two ways. So 2.5mm.


    Mind you, I kid you not, I was once told many years ago that a box tail from E terminal in 1.5 was undersize `cos ringed cpc was equivalent of 3.0mm therefore fuse would not blow in earth fault condition (back in the days when BS3036 was king). Yet that was for a socket on the ring. A spur was OK though in 1.5. Mind boggles dunnit?
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    mapj1:

    No, I think the intention is always that the spurs are wired in the same stuff as the ring, namely 2.5mm. IF you had 4mm radials the 2 socket limit would make no sense.


    In any case the rating of 2.5mmsq is 27A for surface wired or in plaster - which would have been the options when it was being dreamt up. Dont forget that part L and all this thermal stuff ony go t going after the 1984 revisions to the building regs - because until you have central heating the indoor and outdoor temps in all rooms without a fireplace are not so different.




    The 14th Edition updated to 1976 rates 2.5 T&E is rated at 21 Amps in Table 3M. Copper conductors P.V.C. twin and multicore cables, one twin cable with or without earth continuity conductor, single phase a.c. or d.c. Clipped direct to a surface  or on a cable tray and unenclosed.


     A couple of 3kW appliances run from a spur could warm that up a bit.


    Z.


     

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    The 15th edition up to June 1987 in Appndx. 5 clarifies things a bit.(Page 120).


    "The minimum conductor size of conductor in the circuit and in non-fused spurs is given in Table 5A. (2.5mm2).However if more than two circuits are bunched together of the ambient temperature exceeds 30 deg. C, the size of conductor is increased and is determined by applying correction factors from Appndx. 9 such that the size then corresponds to a current-carrying capacity not less than


    20 Amp for circuit A1 (ring) i.e. 0.67 times the rating of the overcurrent protective device)."


    A non-fused spur is allowed to supply only one single or one twin socket outlet or one permanently connected equipment in this edition of the 15th edition.
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    I altered a kitchen wiring of a rewire I did a few years previously, single sockets  for washer and dishwasher  with dp switches above worktop, all labelled.  one heavy load each spur not washer and DW in one twin. This gives easy switching of W & DW and negates the simplyawfull practice of sockets in cupboards. I`d never encorouge two such loads in one twin.


    Same reasoning I always use a 45A DP switch for cooker, not one with onboard socket, that is a throwback to the days of not many sockets per dwelling and OK for kettle now and again but how often do washers/dryers get a home there? Aghh.
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    ebee:

    I altered a kitchen wiring of a rewire I did a few years previously, single sockets  for washer and dishwasher  with dp switches above worktop, all labelled.  one heavy load each spur not washer and DW in one twin. This gives easy switching of W & DW and negates the simplyawfull practice of sockets in cupboards. I`d never encorouge two such loads in one twin.


    Same reasoning I always use a 45A DP switch for cooker, not one with onboard socket, that is a throwback to the days of not many sockets per dwelling and OK for kettle now and again but how often do washers/dryers get a home there? Aghh.






    Although a socket outlet mounted on a cooker panel may encourage misuse and the running of flexes over hot hobs, it is very handy for the customer to make us tea if we have the ring turned off.


    Z.

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