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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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    I suppose that limiting the number of unfused spurs from a ring protects cables from overloading. Having just one single OR one double 13 Amp socket connected to an unfused spur aids fault finding and prevents overloading. It would not be good to have ten double sockets connected on an unfused spur from a ring wired in 2.5mm2 T&E, as the cable could become overloaded if many appliances were plugged in and used at the same time. an unfused spur can run from the origin of the ring (consumer unit) OR from other places on the ring such as existing socket outlets or between  sockets via a junction box. We must remember that the spurs are protected by a 30 or 32 Amp protective device at the consumer unit. Historically the floor area serviced by a ring circuit was limited to 100m2. 


    433.1.204 requires that the current carrying capacity of the cable should be not less than 20 Amps., and if  under the intended conditions of use, the load current in any part of the circuit is unlikely to exceed the current carrying capacity of the cable (Iz) for long periods 433.1.1. is complied with.


    Z.




Reply
  • 0
    I suppose that limiting the number of unfused spurs from a ring protects cables from overloading. Having just one single OR one double 13 Amp socket connected to an unfused spur aids fault finding and prevents overloading. It would not be good to have ten double sockets connected on an unfused spur from a ring wired in 2.5mm2 T&E, as the cable could become overloaded if many appliances were plugged in and used at the same time. an unfused spur can run from the origin of the ring (consumer unit) OR from other places on the ring such as existing socket outlets or between  sockets via a junction box. We must remember that the spurs are protected by a 30 or 32 Amp protective device at the consumer unit. Historically the floor area serviced by a ring circuit was limited to 100m2. 


    433.1.204 requires that the current carrying capacity of the cable should be not less than 20 Amps., and if  under the intended conditions of use, the load current in any part of the circuit is unlikely to exceed the current carrying capacity of the cable (Iz) for long periods 433.1.1. is complied with.


    Z.




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