"Grant" wrote in message
...
Hi,

I want to extend the ring mains in my (1930's) house to add two double
sockets to a room. I've got the floorboards up and know where the new
cable needs to go. However, the thing that's stopping me going ahead is
the fact that the existing cable appears to be ever so slightly thicker
than the 2.5mm^2 that I was going to use. It is also multi(6)-stranded
instead of single-stranded. Is this to be expected with older wiring (I
believe a rewiring was done in the 70's)? There is a 32A MCB at the fuse
box so I thought that 2.5mm^2 would do the job but having seen the
existing wire I now have doubts. I don't want to weaken the installation
by using wire that is too thin.

After a bit of Googling it seems that 4mm^2 cable might be used in a
radial installation but I disconnected the wire between two sockets in the
room and they both still worked - does this allow me to conclude that I
have a ring mains? Also, 4mm^2 cable doesn't seem to be available from
B&Q, etc. - the next size up is 6mm^2.

Maybe the fact that I'm having to ask these questions suggests that I
should get in an electrician?!


It sounds like 7/.029 cable which was the forerunner of 2.5 solid conductor
and ws usually tinned copper conductors.
A simple solution of just using 2.5mm T&E to extend it is possible but
ignores the ramifications of cicuit protective conductor sizing (earth
conductor) and fault currents. However I suspect most of the run of the mill
sparkys might do just that.
4mm cable is readily available from half decent suppliers and some
wholesalers might even be willing to cut lengths for you.
For a fuller answer we would need to know what earthing arrangements apply
to your installation and an idea of possible cable lengths involved. You
have already advised us that you have a 32A MCB but can you tell us if it a
type B or otherwise? If the protection is problematic it might be possible
to use a 32A RCBO but we need answers first