cable size

[martysparky]

can anyone explain why if you spur off the ring to a f/c/u the spur must be 2.5 to supply a 1.5? when would the rating exceed that of the 1.5? is if f/c/u potential change to socket the only reason?

 

[martysparky]

can anyone explain why if you spur off the ring to a f/c/u the spur must be 2.5 to supply a 1.5? when would the rating exceed that of the 1.5? is if f/c/u potential change to socket the only reason?

anybody answering

 

[Deleted member 9648]

Because the ring will be protected by a 32a device at the CU.....not what you would want covering a 1.5mm.
The protective device at the CU should not exceed the current rating of the smallest conductor protected by it, yes I know a 2.5mm is not rated at 32a but the regs make an exception for spurs off a ring allowing a minimum 2.5 to be used.

 

[GKSElectrical]

Hi interesting topic, if you look at the logic behind the spur from the ring to a double socket. say if you loaded each outlet outley to 13 amp total + 26A 2.5 is rated as 27Amp method C clipped direct i now the others dont work out. If you say a 13 amp spur you can only pull 13amps 1.5 is 19.5 method C so it should be ok to feed spur from a ring. I checked the regs to see if it has change but i have installed smaller cables in the past to feed a spur from a ring. if you check out regulation 433.2 see if you or any one else can throw a light onto it, from this i think you can down size providing it is protected at the other end and no longer than 3mts.

 

[martysparky]

Because the ring will be protected by a 32a device at the CU.....not what you would want covering a 1.5mm.
The protective device at the CU should not exceed the current rating of the smallest conductor protected by it, yes I know a 2.5mm is not rated at 32a but the regs make an exception for spurs off a ring allowing a minimum 2.5 to be used.

yes clear discription and that applies to what I mean but what I'm saying is when an FCU is in the design supplying sockets for example.


so it would be: 2.5 / FCU / 1.5 - socket ( load side) as per picture in BRB.

Why not: 1.5 / FCU/ 1.5 - socket( load side) we know only one socket from an unfused spur but there is a potentialfor a DIY FCU change to socket?

If it where 2.5 / FCU / 1.5- socket (load side)/ onto FCU (from supply side) / 1.5 - socket ( load side) would that be acceptable clipped direct? or would it be better practice to extend the ring to the first FCU? I know what I would prefer to do but what is acceptable?

 

[martysparky]

Hi interesting topic, if you look at the logic behind the spur from the ring to a double socket. say if you loaded each outlet outley to 13 amp total + 26A 2.5 is rated as 27Amp method C clipped direct i now the others dont work out. If you say a 13 amp spur you can only pull 13amps 1.5 is 19.5 method C so it should be ok to feed spur from a ring. I checked the regs to see if it has change but i have installed smaller cables in the past to feed a spur from a ring. if you check out regulation 433.2 see if you or any one else can throw a light onto it, from this i think you can down size providing it is protected at the other end and no longer than 3mts.

That is pretty much the way I read it too, Providing there is no branches meaning other un-fused pull on the supply side.