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Though not a great lover of the OSG there are some good guides in it and one is the 1/8 one (Page 68 Section 7.2.3) , that an unfused spur length off of a ring should not exceed 1/8 of the furthest point of the ring.
The 3 metre ruling would not apply to a RFC simply because
1) Your concerning yourself with the overload side of things, or you should be. The earth fault protection should still be provided by your 32amp protection device provided that the spur would not exceed that Zs value for that device. Which is why the 1/8 rule is pretty good, if you ensure this there is very little chance your spur will fail on Zs
So it is more the over load side your concerned with, that is a single 2.5mm cable being protected by a 32amp PD. Well that is where I agree with you concerning a spur should only connect into a BS 1363 accessory, because these accessories all are limited to 13amps and you therefore conform to reg 433.2.2
This is why I always say to guys who ask can I spur of a ring final into an enclosure and just put 6amp for lighting and a 10amp for socket no. IMO it is a bad design and opening the design up to abuse
Yes in theory you can, that 16amp load will not stress a 2.5mm cable. But even in a domestic situation there could be a chance that you may have a problem with a socket(s), you may have a fridge/freezer on it and a washing machine and it may just trip occasionally when the heating element is on and the fridge starts up, so what happens ,the MCB is increased to perhaps a 16amp or even more.
By designing a spur into a non BS 1363 accessory is opening up that circuit to abuse in the future and IMO bad practice.
The 3 metre ruling would not apply to a RFC simply because
1) Your concerning yourself with the overload side of things, or you should be. The earth fault protection should still be provided by your 32amp protection device provided that the spur would not exceed that Zs value for that device. Which is why the 1/8 rule is pretty good, if you ensure this there is very little chance your spur will fail on Zs
So it is more the over load side your concerned with, that is a single 2.5mm cable being protected by a 32amp PD. Well that is where I agree with you concerning a spur should only connect into a BS 1363 accessory, because these accessories all are limited to 13amps and you therefore conform to reg 433.2.2
This is why I always say to guys who ask can I spur of a ring final into an enclosure and just put 6amp for lighting and a 10amp for socket no. IMO it is a bad design and opening the design up to abuse
Yes in theory you can, that 16amp load will not stress a 2.5mm cable. But even in a domestic situation there could be a chance that you may have a problem with a socket(s), you may have a fridge/freezer on it and a washing machine and it may just trip occasionally when the heating element is on and the fridge starts up, so what happens ,the MCB is increased to perhaps a 16amp or even more.
By designing a spur into a non BS 1363 accessory is opening up that circuit to abuse in the future and IMO bad practice.
