Earthing Q - new pattress won't fit original metal conduit

[sparkwright]

I've got an old imperial coupler and bush here at home (I save things like that, you never know mother) and a box with a 20 mm hole, and they scarcely touch when you connect them together - so you need to think about drilling smaller holes with a step drill.

You may be lucky and find a box where the holes are similarly spaced apart, and the bushes each just about make good enough contact - placing a lock ring in between may help - but new holes are by far best.

 

[333rocky333]

Thanks all.

Get a different make of box, or try it upside down. It's the 25mm knockout that's cocked you up.

Sadly not the case re the 25mm knockout - if only it were that easy.

Pretty sure some dont have the 25mm knockout, just 4 x 20mm ones spaced different, as far as i know hole spacings have been pretty standard for years

Post a pic of the bush, metric ones usually have a slit cut in the head

 

[RF Lighting]

It's the old half inch imperial conduit, so it's never going to connect to a modern box with 20 mm knockouts SUCCESSFULLY.

As I said, you can drill new holes in a new box, but the main problem is the pre-formed knockouts might open out as you're drilling. Can be done with care though.

Never spotted that! Yes it's ½" conduit, not ¾" as I'd assumed, so drilling out a blank box is the only way to do this properly.

 

[blackworx]

I've got an old imperial coupler and bush here at home (I save things like that, you never know mother) and a box with a 20 mm hole, and they scarcely touch when you connect them together - so you need to think about drilling smaller holes with a step drill.

You may be lucky and find a box where the holes are similarly spaced apart, and the bushes each just about make good enough contact - placing a lock ring in between may help - but new holes are by far best.

It's 3/4" conduit, so the 20mm knockouts on the new back boxes are marginally smaller rather than way too big.

There was a pair of lock washers used on each entry, which I will either replace (if I can find ones to fit) or clean up and reuse. My original pic didn't show these as it was just to illustrate the spacing issue.

 

[bernardgreen]

This may not comply with regs,

Remove most of the side box where the conduits are,

Use the bushes to fix banjos to each of the conduits, Clean the conduit ends to bright metal to ensure good contact with the banjos.

Link the banjos together to provide earth continuity between conduits and extend the connection to the box's earth terminal and the socket's earth terminal ,

 

[sparkwright]

3/4 inch eh?

Ah, that's different.

You may be able to get a box to fit with a bit of modification.

I take it there are some brass bushes as well somewhere, not shown in the pic?

 

[OwainDIYer]

It really would be easier just to drill a new box to fit ...

 

[sparkwright]

Can you get 'plain' boxes?

 

[Adam_151]

3/4" is just a nats over 19mm. Cutter bits tend to make a baggy hole anyway, so a 20mm hole might not be sound.

both 19mm hole saws and 19mm punches seem to be available (If trying to use a box that already has knockouts, you might get on better with the punch)

 

[OwainDIYer]

Can you get 'plain' boxes?

MK K830 ALM

 

[sparkwright]

Can you get 'plain' boxes?

MK K830 ALM

Apologies for being dense, and I may be looking at the wrong item, but the nearest I can find is surface mounted (ie no good) boxes which presumably have knockouts.

 

[333rocky333]

best MK does is a 25mm 862 ZIC or a 35mm 886 ZIC, unless reystyled these used to have just two knockouts on the underside and scope to drill either side of them

EDIT
looks like the 862 now has 4x20 knockouts
and the 886 now has a combo of 20 and 25 like you have.

 

[333rocky333]

Can you get 'plain' boxes?

MK K830 ALM

Apologies for being dense, and I may be looking at the wrong item, but the nearest I can find is surface mounted (ie no good) boxes which presumably have knockouts.

That part is a surface box with no knock outs, generally used to mount MK logic sockets when using surface mounted 25mm galv conduit