Cable size 100amp switch to RCD Ask questions and find answers to many subjects relating to electrics and electrical work

[stefanm]

What cable size should be run between the incoming 100 amp switch and the RCD in the distribution box?

[ericmark]

25mm cable would be the norm but it really needs calculating and even if 10mm cable was used one could not without measuring and calculating say it was wrong.

Most people would fit 25mm to avoid any problems in trying to prove to the supplier it was big enough.

Although you say 100A switch you have not stated the size of protective device and of course one would likely still use a 100A switch on a 60A supply.

I am trying to be careful as it is so easy to add 2 and 2 and get 22 and so answers where all details are not given can very easy be wrong.

[stefanm]

Thanks for the reply ericmark - just to elaborate the RCD is 80A 30ms. Main switch is 100A and supply fuse is 100A. I need to replace the cable between main switch and RCD as I can see the bare conductor and the cable is too short to re-adapt. The existing cable looks to be 10mm and has the words 'Live Supply 80A max'. I thought about replacing with a 10mm core of twin & earth but this is not as flexible as the existing cable - so is there a different spec of cable used for this function?

[ericmark]

Yes special cable is used with double insulation. In general a wire is used where there is protection as inside conduit or trunking and where there is no protection than some form of double insulation is used. Twin and earth has the grey outer and this should not be removed unless it is inside some protective device like a socket box or consumer unit. 6181Y 25mm Cable 5m Brown/Grey and 6181Y 25mm Cable 5m Blue/Grey cost around £13.12 each so would not think £26.24 is really going to break the bank? (Screwfix price) they are listed as Meter Tails
PVC insulated single core Meter Tails (6181Y). For connecting CUs (Consumer Units) and switch fuses. Harmonised colours. So can't really make any mistakes getting right stuff.