Drill size for lighting cable

[Jupiter01]

Hi,

I need to push 1.5mm cable through a cavity wall and wanted advice on the size of the hole so that I can buy a long bit accordingly.

Also, will it be okay to drill from the inside (will be a lot easier for me). Or will the hammer drill damage the brick on exit?

thanks

 

[sparkwright]

Typically you would drill a 10mm hole.

On a cavity wall I have found it more favourable to carefully measure - and drill a hole from inside to the cavity. Then drill a hole from the outside to the cavity. No damage this way.

Then use an unfolded wire coat hanger to locate the route through, and tie the cable to this, then draw through.

For this process a 20mm hole is much easier, on one side of the wall at least. Otherwise it will be a struggle.

 

[Iggifer]

10mm will be fine for a single 1.5mm²

As to drilling in/out. It really depends were you're drilling to/from. If you're drilling out of the back of a backbox etc, you've got to drill out.

If you're drilling elsewhere, and can measure it well enough, drill outside in.

You're gonna blow out inside if you drill in, but you can patch plaster much easier. If you have to drill out, try and work out when you're getting close to the end of the hole and ease off on the pressure a bit

 

[Iggifer]

On a cavity wall I have found it more favourable to carefully measure - and drill a hole from inside to the cavity. Then drill a hole from the outside to the cavity. No damage this way.

That's a good tip! But I don't think my measuring's up to that!

 

[sparkwright]

On a cavity wall I have found it more favourable to carefully measure - and drill a hole from inside to the cavity. Then drill a hole from the outside to the cavity. No damage this way.

That's a good tip! But I don't think my measuring's up to that!

I do it a lot now, as I hate damaging plaster, render, brickwork.

It's quite easy to do, especially if you have something like a window that you can use to measure off from, both inside and out.

With largish holes, say 20mm, the wire coat hanger should find it's way through both holes, even if they are about an inch out of alignment.

 

[Jupiter01]

thanks all. Very helpful as always.

 

[PrenticeBoyofDerry]

I drill inside to out with a pilot, if you measure the total wall depth, then take the drill from hammer to rotary/percussion for the last inch, this will reduce potential damage. I then drill from both sides inwards towards the cavity with the drill sized required for the hole.

 

[DaveHerns]

Don't do it the way Virgin Media did it on my house. SDS hammer drill, blunt drill and lean on the drill with all your weight so half the brick blows as it bursts through. Then silicone one of those ugly plates to the wall.

 

[ban-all-sheds]

I need to push 1.5mm cable through a cavity wall

Why?

Where will the cable go one it's outside?

Also, will it be okay to drill from the inside (will be a lot easier for me). Or will the hammer drill damage the brick on exit?

As said, it will spall whichever way you go, and damage inside will be easier to make good, particularly if there's going to be an accessory like a switch or FCU there.

PBoD's method is best.

Don't forget to angle the hole downwards (in -> out).

 

[Screech20]

please make sure whichever way you do it, that there is nothing the other side of the wall that you're drilling.
Got called out last week after a plumber drilled his 10mm pilot bit inside to out, smack bang (literally) into the main service cable!

 

[ban-all-sheds]

That will be the flip side of the time I drilled through a pipe. Fortunately not the incoming main though...

 

[OwainDIYer]

Drill right the way through the wall with a thin bit to establish the position with minimal breakout. Then drill from each side 20mm and push through a 20 mm plastic conduit.

 

[Spark123]

I'd go with the pipe idea too, then your cable will be protected in the cavity from any falling debris or if polystyrene insulation is present.

 

[Jupiter01]

Is a conduit necessary? How do most people pass cables through a cavity? I'm getting the sense that they just push the cable through.
Also, since I am first fixing at the moment and not connecting the exterior light, is it okay to leave the cable dangling out (exposed to the weather) with some insulation tape on the end?

 

[sparkwright]

In the real world no one bothers with conduit passing through the wall.

You could tape up the end for the time being, though there's a chance it will become live then you should blank the end of better than that.