old cooker switch/socket

[bhoy70]

I dont use my cooker switch/socket,that comes straight from 45 amp fuse on fuse board.Was wondering if this is ok to do,I would like to take switch/single socket out,and replace with double socket,then add another 2 double sockets,thus making a radial circuit.I have 6mm cable coming from fuse to cooker switch,is it ok to leave this,and then use 2.5mm cable to other sockets i would like to put in.I also have been told i would have to change 45 amp fuse,to 30 amp.Any help and info on this would be great.cheers

 

[davelx]

2.5mm T+E is rated 27A max, so 30A fuse is no good (30A is ok for a Ring Final as you have 2 X 2.5mm cables).

Assuming we are talking BS3036 re-wireable fuses here, there is a derating factor of 0.725, so the best case current handling for 2.5mm (cable clipped direct to wall or equivalent installation method, ie no other derating factors) is 19.575 A - so you would need a 15A rewireable fuse on this circuit.

If you wire the additional sockets in 4mm, you could increase the fuse to 20A (again assuming no other derating factors other than that for the 3036 rewireable fuse).

If you use 6mm, then you could possibly use a 30A fuse, but getting 2 x 6mm cores in the socket terminals might be a problem.

If there are other de-rating factors due to how the cable is installed, then the fusing would have to be reduced accordingly.

(If you have MCBs rather than 3036 rewireables the situation is different as the 0.725 derating does not apply - but your mention of "30A fuse" suggests otherwise)

(NB: all figures from 16th Ed as I've not memorised the 17th Ed info yet)

 

[bhoy70]

Thanks for that dave.
I have rewireable fuses in place,in the near future, i will be getting it changed over,but thats what is there for now.So if i keep the 6mm cable from fuse to what will be first double socket,then use 4mm cable to other 2 sockets,a 20 amp fuse will be ok.I will be getting qualified sparky to do the work,but i like to know what is getting done beforehand.

 

[davelx]

There is also the issue that the regs now require all socket outlets <20A rating to be RCD protected. So your sparky will need to install an RCD on this circuit.

This could be done using a small enclosure next to the existing CU, but this requirement may influence your decision of when and how to rewire.

There's a number of approaches that you could take to make the future rewire easier/cheaper. Parts used for this initial modification could be re-used during the rewire, for example. Best to discuss with your electrician.