Spur off lighting circuit

[nitro23456]

In my loft I have a junction box which has been added so that the existing lighting circuit can supply a spur for a switched loft light.

Is it permissible to use this same junction box to add another spur for an outside security light?

Separately, what size drill bit would you advise for 1mm twin an earth cable through a cavity wall?

 

[flameport]

Is it permissible to use this same junction box to add another spur for an outside security light?

Probably.

Separately, what size drill bit would you advise for 1mm twin an earth cable through a cavity wall?

22mm.

You then fit a short piece of 20mm conduit through the wall and pass the cable through that.

 

[ColJack]

according to sources, 1.0mm² T+E is about 8mm x 4.5mm.. ( differs from manu to manu.. )

so anything about 10-14mm should do the trick.. oh and about 600mm long..