Advice on fitting an external light

I'm in the process of fitting an external light (beside the front door) which will be controlled by a switch inside the front door. I was planning on picking up my power supply from the ceiling light inside the front hall. My main concern is with the routing of the cable through the exterior wall.

It was my intention to drill a whole through the external cavity wall and route the cable from the external light through the hole (The cable will not be directly exposed to the elements as the external light will be mounted on top of the newly drilled whole). The cable would then be routed up a channel cut into the plaster eventually coming out at the light switch.

The new light is 35watts so I was intending to use 1mm twin and earth lighting cable.

So my questions are...

1. Is my choice of cable suitable?
2. Is it OK to directly plaster over this cable where is has been internally routed?
3. My main concern. How do I preserve both the electrical safety and damp proofing where the cable is routed through the cavity wall?

With regard the question 3, to prevent moister tracking along the cable I was going to drill the hole at a slight upward angle. Should I use mastic to seal the external hole after the cable has been put in? Do I need to further protect the cable with some conduit inside the cavity?

Any other tips or tricks would be greatly appreciated.

Regards

BoxOfFrogs said:

1. Is my choice of cable suitable?

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Yes.

2. Is it OK to directly plaster over this cable where is has been internally routed?

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Yes, as long as it runs vertically in line with the switch. Don't forget it should be RCD protected though...

3. My main concern. How do I preserve both the electrical safety and damp proofing where the cable is routed through the cavity wall?

With regard the question 3, to prevent moister tracking along the cable I was going to drill the hole at a slight upward angle.

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Good Idea.

Should I use mastic to seal the external hole after the cable has been put in?

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You should.

Do I need to further protect the cable with some conduit inside the cavity?

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That isn't necessary, but:

i) it might be easier to thread the cable through if you've got conduit there.
ii) using conduit will mean no worries about plasticiser damage if you have cavity wall insulation installed later.

Any other tips or tricks would be greatly appreciated.

Click to expand...

You'll need some long drill bits, as the chances of lining up two independently drilled holes are approximately zero.

Drill the holes in at least 2 stages of increasing diameter - having gone right through both leaves in one direction widen the hole going the other way to minimise spalling on the outside surfaces.

Thanks for the promt reply.