Dropping a cable through cavity wall.

[Andrew Barnes]

Hi There

I need to drop an alarm cable down through a cavity wall. Any hint/tips about how to do this?

Thanks

Andrew

[Dave Plowman (News)]

Normal way is to use a 'mouse' - a small but heavy weight on string. Lead is best. Then fish out the string at the bottom using a wire hook.

[Andy Burns]

In practice brick ties can get in the way, one tip I've heard is to poke a large loop of net curtain spring wire in to your exit hole to act as a catcher ...

[Christopher Key]

Mungo Henning recommends attching a short piece of ferrous chain to the end of length of string, and a fishing it out down below with a magnetic, telescopic wand.

I've had excellent results with this technique, using some 'Kite String' I bought at a kite festival a while ago. It is ideal for this, as it is very light and smooth, so doesn't tend to catch, but is also really quite strong; certainly plenty strong enough to draw through something very much stronger.

It's also far easier job if you're careful drilling the holes so that they are exactly above one another, and if you have two people doing it.

Hope this helps,

Chris Key

[Brian Reay]

Accurate measuring to get the holes as near to vertically aligned as possible.

Small torch to shine into lower hole- often you find the line is exactly in the place it should be. If not, a little 'wiggling' will usually allow you to hook it with a bit of coat hanger wire etc.

I've also used an old flat retractable tape measure in the past. Fold in half and push the loop into the lower hole. It tends to 'spring out' in the cavity making a large loop you can 'drop' the weight into. When you pull the tape out, the string comes with it.

Always tie a spare string to the first and pull it through with the cable. If the cable comes adrift, you still have a string in place to try again.

If the cable in thick, make the first 6" more flexible by stripping the outer insulation, or it may snag, rather than "bend", into the hole.

[Andrew Barnes]

Thanks for all your help, i'll get a strong line and give it a go!

Thanks

Andrew

[Bob Eager]

Flexible tape measure works well and can conform pretty well to the edges of the cavity; make the loop big enough to circumnavigate the area at the bottom.

[Paul ( Skiing8 )]

My tip is to drill the top hole first and then use the string and weight as a plumb line to line up for drilling the bottom hole.

Paul

[Lurch]

On Tue, 1 Feb 2005 10:45:04 -0000, "Paul \( Skiing8 \)" strung together this:

Obviously only useful when doing it all in one room, I only really drop things in cavities when it's going over 2 storeys.

[Set Square]

All this discussion so far seems to have assumed that the cavity is full of fresh air!

Surely, everything built for a good few years now will have cavity insulation - and a good many older properties will have had the cavities insulated retrospectively.

Doesn't this make the job more difficult - if not impossible?

[Bob Eager]

Fairy nuff. I was thinking of internal walls - tho' with the term 'cavity' I perhaps should have thought otherwise.

[Lurch]

On Tue, 1 Feb 2005 13:22:20 -0000, "Set Square" strung together this:

There is that, I had assumed an empty cavity, if it's full of insulation then you're pretty much stuffed.

[Set Square]

Well, if you're talking about stud partition internal walls, you've got a different set of problems - because there are horizontal noggins which get in the way!

[Michael Chare]

If you attach the string to a piece of bent wire at the top you can swing the 'mouse' which may make it easier to find at the bottom.

[Bob Eager]

Yes...I was wondering why people hadn't mentioned them. Mind, in one case I was lucky enough to find no noggins! Quite a narrow bit of wall though..

[Gary Cavie]

I recently had to get a coaxial cable down a wall which was full of insulation. I used a set of cable rods, drilled the lower hole first, then carefully measured up in the loft. Pushed the rods down, keeping them tight against the inner skin, with a piece of string tied to the end. When I came down from the loft, and shone a torch through the hole, the rod and string were there!

I don't suppose I could do it again if my life depended upon it!