by ericmark »
Tue Mar 10, 2015 12:13 am
Yes OK to sleeve. There was a big discussion over the over sleeving of an earth wire when using three core flex for items like cistern thermostats some thing which I would have considered a big no. But the Electrical safety council has it on there web site that even this is OK. With singles no not permitted but with twin and earth yes no problem with line and neutral to over sleeve. You could not over sleeve the bare cable to be anything but earth because it's not insulated the line and neutral is no problem.
However twin and earth cable in for inside use only so unless the garage is attached to the house in some way then twin and earth is not suitable it really does not matter what colour it is.
Cables used outside are normally black to resist UV from the sun. Normal would be SWA cable but there are other options.