Which box to use with 25mm SWA glands?

[Fred_Fanackapan]

I wish to terminate SWA cable into a plastic CU and switch fuse. I'm using BW-25 glands which require a 25mm dia mounting hole.

I have some adaptable boxes but they only have 20mm knock-outs. Are there bigger metal boxes available? Cannot see any at TLC.

 

[Chri5]

http://www.tlc-direct.co.uk/Products/FXTHS25.html

 

[ban-all-sheds]

http://www.rapidonline.com/sku/Tool...ts/Circular-sheet-metal-punches/34566/86-5315

 

[ban-all-sheds]

Actually - neither a holesaw nor a punch will be much use for enlarging a 20mm hole to a 25mm...

Just poke out the 20mm KO and have at it with one of these

Or - some of the larger MK grid boxes have 25mm KOs (possibly so do the metalclad accessory boxes, but I'm not sure how easy it is to get those on their own). So if you can get a blanking plate for one....

Or - get a 25mm 2-way conduit box, a 25-20mm reducer and some 20mm flexible conduit. SWA gland in one side of the box, reducer in the other, flexible conduit to carry the SWA cores and earth conductor for the box into the CU. That might also give you useful flexibility in where you terminate the SWA.

Or - a short length of 50mm or 75mm metal trunking running along the bottom or side of the CU.

 

[electronicsuk]

I've never had any problems taking a 20mm knockout to 25mm with a holesaw. I can see how using a punch would be problematic, though.

 

[ban-all-sheds]

With no pilot, won't it skid around all over the place?

And with a pilot, how do you stop that from removing the KO as soon as you put any pressure on it?

Now, a stepped cone cutter.....

 

[electronicsuk]

With no arbor, won't it skid around all over the place?

Indeed it would. It only works if you haven't removed the KO!

And with an arbor, how do you stop that from removing the KO as soon as you put any pressure on it?

By using a sharp pilot drill before going through with the bit integrated into the arbor, such that you're not putting much pressure at all onto the knockout in the vertical axis.

 

[Monkeh]

Now, a stepped cone cutter.....

Or unstepped. Just put the earth tag around it.

 

[RF Lighting]

I've got a holesaw arbor with an extra long thread. It allows you to put two holesaws onto the same shaft, i.e. a 25mm holesaw with a 20mm holesaw inside it. It's great for opening existing holes up.

 

[Lectrician]

Sterrat do one like that marketed as an "oops arbour".

A cone cutter would do the job.

 

[Fred_Fanackapan]

Thanks for the suggestions so far.

The boxes I have have 2 20mm KOs per side and I would like the 25mm hole in the centre of the side. This would mean cutting into 2 20mm KOs. Would the hole cutters work in such a situation?

Thinking about it, I think BAS's suggestion of using conduit is a great idea. Now to look for some suitable conduit boxes.

 

[sparkiedave]

if the knockout is already missing just clamp a block of wood in the box for the pilot to locate into

 

[ban-all-sheds]

Thinking about it, I think BAS's suggestion of using conduit is a great idea. Now to look for some suitable conduit boxes.

Widely available.

http://www.tlc-direct.co.uk/Main_Index/Conduit_Steel_Index/25mm_Conduit/index.html

http://www.tlc-direct.co.uk/Main_Index/Conduit_Steel_Index/25mm_Conduit_Boxes/index.html

 

[Fred_Fanackapan]

So the gland would fit directly into one of those boxes?

 

[ban-all-sheds]

Yes - the threads are compatible.

As they are for the adapters on flexible conduit, hence my suggestion for a 25-20mm reducer, unless you want to use 25mm flexi.