Back box with 20mm center punch out

[wrightsonm]

Is it possible to buy a metal 1 gang back box that has a center punch out at the top rather than left and right punch outs?

I already have these:
https://www.screwfix.com/p/appleby-galvanised-steel-knockout-box-1g-35mm/52143

However the existing conduit in the wall is center aligned to the back box hole.

If i were to drill out a 20mm hole i'd end up with a huge gap as the punch outs either side give way and the grommit then surely wont fit properly

Thanks
Mark

 

[oldbutnotdead]

Have a look at these https://www.toolstation.com/axiom-metal-clad-20a-dp-switch/p60636 or similar- not sure if you can get the backboxes on their own but looks like they have lugs on all 4 sides. Might need to check the actual switch you're using, make sure the hole centres line up & be prepared to bin off the top and bottom lugs when they get in the way of the switch along with being very careful about no exposed copper outside the switch terminals.
EDIT Just looked on TLC, they have a Telco metalclad range which looks to have a centre single hole https://www.tlc-direct.co.uk/Products/AA3712.html or there's this little bargain here https://www.toolstation.com/axiom-metal-clad-blank-plate/p15062

Of course if you're working with conduit you could just put a coupler and a bush on, or a nipple and a nut (depending which way the stuff is threaded)- anything that gets you past the sharp edges

 

[rsgaz]

If you have the depth, some manufacturers have a centre hole (25mm usually) on their 47mm deep boxes...

 

[wrightsonm]

That is exactly what im looking for. Except 47mm is too deep. 35mm is ok though. Which manufacturer is that?

@oldnotdead - they look like surface boxes. Im really looking for recessed boxes.

 

[oldbutnotdead]

That is exactly what im looking for. Except 47mm is too deep. 35mm is ok though. Which manufacturer is that?

@oldnotdead - they look like surface boxes. Im really looking for recessed boxes.

They are designed as surface boxes, nothing stopping you setting them in the wall though

 

[rsgaz]

Which manufacturer is that?

That particular one is from here...

https://www.cdlmicro.co.uk/cdl-bb05...l-back-box-pattress-box-25mm-deep-1-gang.html

drill out a 20mm hole i'd end up with a huge gap as the punch outs either side give way and the grommit then surely wont fit

You could use a 'short bush' and lockring/locknut instead of a grommet. That would be able to grab what's left of the box, even if the knockouts either side snag and fall out when drilling.

 

[wrightsonm]

Maybe what ill try is putting a wooden support inside to minimise breakout, then drill, then fix with a bush as you suggest.

Or maybe I should just chisel out the back box hole left or right by an inch and then replaster!