Plasterboard and metal back boxes

[OldKettle]

Hi,
What is the best depth for a metal back box when installed in a batten and plasterboard wall?

Should the front of the metal box, ideally be flush with the front of the plasterboard, or slightly deeper/proud?

Does the ideal depth change if the plasterboard is to be tiled?

If the front of the box doesn't quite reach the back of the plasterboard (therefore leaving a gap) is that a problem?

Any thoughts would be much appreciated.

 

[RF Lighting]

The ideal depth is the deepest box you can use. Generally 35mm for standard accessories.

The box wants to be at most flush with the plasterboard surface before it is skimmed. If it is deeper it’s not a problem. If the box ends up more than 25mm below the plasterboard surface, you can buy extension pieces to make the box deeper.

 

[SimonH2]

Yes, tiling does change things - it gives you a bit more leeway. Other than that ...
As above, the box should be nearly flush with, but not proud of, the board surface. That way, when the wall is skimmed, the plasteter can work the plaster into the small gap around the box and as it's going off, remove the excess that will inevitably encroach into the box.
What you really, REALLY, do not want are huge holes in the board and the boxes half a mile (yes I know, I've been told millions of times not to exaggerate ) deep behind it. Seen that a few times (builder CBA to cut the boards accurately), and inevitably the plasterer can't fix that without a lot of effort he's not being paid enough to do. You end up with the accessories not covering the holes and pulling into the void when you tighten the screws.