"JoeJoe" wrote in message
o.uk...
On 07/12/2015 18:34, ARW wrote:
"Dave Plowman (News)" wrote in message
...
In article ,
JoeJoe wrote:
One of the sockets that I need is now hidden behind a chest of drawers,
so I want to have a new one only about 1m away.

My plan is to disconnect one of the two cables going into the socket
(it
is definitely part of the upstairs ring, not a spur), extending it to
reach the new socket, and run the return back to the original socket.

Why not simply spur from the original?


Because electricians and DIYers keep banging on about how much better it
is to extend the ring?

Where in the real world a spur is fine for almost every application.

First time I heard that from an electrician!

What about running the cable(s) through the celotex? Are there any rules?

Just wondering as it is likely to carry relatively high current.

It is not going to be carrying a relative high current. It will carry a
short term 10A load when your wife dries her hair

Would making the hole(s) slightly larger be enough?

It makes no difference if you extend the ring or use a spur. You should
ensure sure that the current carrying capacity of the cable does not drop
below 20A.

Appendix 6, table 6B of the OSG covers your proposed installation very
nicely.

The CCC of 2.5mm T&E without any derating is 27A.

Passing the 2.5mm T&E through insulation gives a derating factor (determined
by the length of insulation) as


100mm = 0.78 derating factor so your CCC is 21A.


--
Adam