Back box screw hole positions

[endecotp]

That’s supposed to be part of a cross-section of a wall lining with two layers of plasterboard (grey) with a gap between them (say 25mm) for cables, pipes etc. I’ve just seen builders next door constructing something very much like this.

Red thing is a back box for the switch (or socket) in green.

Looking at metal back boxes, they all seem to have fixing holes on the back, and near the front edge of the sides. In my sketch, I’d like to secure the box to the wooden batten (blue). But none of the holes is in the right place.

So do boxes in this sort of construction just get screwed into the back layer of plasterboard?

 

[Luckyphil]

Just use a Plasterboard Box , cut it it to suit & the Screw Tabs pull up to secure it

Phil

 

[Luckyphil]

 

[endecotp]

Yes, I’m familiar with those...

Some people worry they might pull out, or similar. They are useful mainly when fitting into an existing wall.

 

[Taylortwocities]

I have installed hundreds of those. Never ever had one "pull out, or similar"

 

[endecotp]

Well I’ve also fitted a few. But that wasn’t the question!

I’ve been watching a refurb for a few months, and the wall construction in at least kitchen and bathroom involves two layers of plasterboard with a gap for pipes and cables. I think they had fitted metal back boxes and run wires before adding the second sheet. (I guess you can push the PB up and it leaves impressions where you have to cut for the boxes?). Or maybe this was all in my imagination....

 

[oldbutnotdead]

Just drill some holes in the backbox where your bits of stick are.
Those drywall backboxes are fine in 12.5mm or thicker pb that has been fixed at recommended centres. 9mm board or big unsupported section maybe would wobble about

 

[Taylortwocities]

Note, plasterboard mounting boxes are 35mm deep, so make sure you have that depth to house the box.

 

[securespark]

You can't fix the metal box to the PB.

The metal back boxes have holes near the front (top and bottom) which you can use to nail or screw into the ''blue'' wood.

If these are in the wrong place then you can drill holes in a more suitable position.

 

[securespark]

https://www.wickes.co.uk/Wickes-Met...JzFpnPb8C5qnpsaMtP6isUbrY0HyhL8xoCtWAQAvD_BwE

These boxes just have one hole on each side but there are others (or at least were) who made boxes with 2.

 

[Adam_151]

If you need a hole where there isn't one, then just drill one. Try and use pan head rather then countersunk screws to avoid having a an edge to catch cables on.

Normally metal boxes are screwed through the back to either masonary or a wooden batten behind, I wouldn't be happy about a fixing straiht through back into plasterboard as it'll pull out after not very long at all (unless a batten is fitted behind that plasterboard and the screw goes right through). Adapt as you need to, if you have got wood below the box or to the side, then drill and fix as required

 

[endecotp]

Note, plasterboard mounting boxes are 35mm deep, so make sure you have that depth to house the box.

Aaarrgghh. I should have checked this more carefully. Yes I had about 37 mm, BUT:

I seem to have two different kinds of plasterboard backboxes. The one on the right, by Axiom from Toolstation, is 35mm deep. The one on the left, by Appleby from Screwfix, is also 35mm deep. The difference is that the left one needs at least another 10mm behind when fitting as the yellow bits stick out behind until you swivel them into place; the one on the right doesn’t need any extra depth. I think the blue one is also removable, whereas the yellow one would have to be destroyed to remove it once fitted.

Yet another job that has taken five times as long as it should have done....

 

[Sureitsoff?]

the yellow ones can be removed if needed. use a screwdriver to lever the yellow bits out, you might think they will break but i havent managed to break one yet! the blue ones if remember correctly actually require the blue bits to be pushed all the way to the back of the box before they will move to the centre to enable you to remove the box (i prefer the appleby ones) if you pull the yellow bits in to the centre they dont need any more room at the back and as you need to pull the yellow bits in anyway to get the box in the hole....

 

[endecotp]

the yellow ones can be removed if needed. use a screwdriver to lever the yellow bits out, you might think they will break but i havent managed to break one yet!

Levering out the yellow bit requires that the little arm at the bottom of that picture pops back inside the box; does that really happen without it breaking off?

the blue ones if remember correctly actually require the blue bits to be pushed all the way to the back of the box before they will move to the centre to enable you to remove the box

Yes, and it’s useful to know that! But that doesn’t cause anything to stick out behind the body of the box, so you don’t need any extra depth.

if you pull the yellow bits in to the centre they dont need any more room at the back and as you need to pull the yellow bits in anyway to get the box in the hole....

You can get it into the hole yes, but then you need to push them back before pushing them out, and it’s at this point that you need the extra depth:

 

[Sureitsoff?]

Levering out the yellow bit requires that the little arm at the bottom of that picture pops back inside the box; does that really happen without it breaking off?

yes as there is no slot for the "arms " to fit into, it seems brutal but it does work. and the yellow bits will be able to be pushed out with them level with the base of the box (i have just checked) one make of box had the securing lugs pivoted on pegs on the inside corner of the box but i dont think they are still available