As you most likely know about every European country has got its own switch boxes for installing flush-mount switches, outlets,... Now some manufacturers don't seem to think this is enough... they market their own proprietary boxes!
I stumbled over this yesterday... I work for an electrical planning office and a work mate had some trouble with one project. The architect had specified a super low profile series of switches that needs special boxes. It can be mounted in regular 58mm round switch boxes, but the it protrudes pretty far from the wall. The manufacturer doesn't state this anywhere and the electrician put in regular boxes . Now they realized the switches and outlets don't fit... and the walls are extra hard exposed architectural concrete...
So it looks like in the future we're in for a lot of fun!
Yeah, Good point Ragnar!. Over here in NZ, we have the standard depth mounting block, which by memory is 23mm deep. If you need any more depth than that, I think the deep one is 57mm deep. Of course, with any sort of concrete walls (not block walls) everything has to be either chased into the wall (not a thing I've ever been keen on) or run in exposed conduit (ugly, if it's not done properly). Pretty much here, if you want to create a "white elephant" product, design it with a box that is different to the standard size one here. There was a line of light dimmers here a couple of years ago that seemed to disappear off the face of the earth after a couple of months, reason being, it didn't fit into a standard box, because of the size of the heatsink and quite frankly, there would be no way I would be having a device that large on any of my walls, this thing was HUGE, compared to the size of a standard switch-plate here.
These boxes not only need to be deeper but also have a rabbet run around the front (about 1cm deep) to accept the extra-flush devices. Without the rabbet the switch will protrude from the wall, exposing a black plastic side instead of the brushed aluminum designed to be visible.
Where there's new exposed concrete work, usually all conduits and boxes are set into the forms before the concrete is poured, so no trenching. In this case the electrician missed this though and put regular round 58mm boxes in the forms... and we're talking a big building here... Austria's fanciest "museum" of modern art (stuff like holograms and whatever, really high techy).
Some architects also started forcing electricians to use Italian rectangular boxes in Austria a few years ago, so I guess we'll end up with quite a lot of different box types here (an Italian 3 module box is pretty much the same size as a US single gang box, I think using metric screws a US duplex receptacle or switch would fit).
On top of this you might encounter old 2 and 3 gang boxes that were smaller than new ones... namely shorter. You can fit a new double gang switch to an old box, but I don't think there's a way to cram a 3 gang into an old box. I think it's about 5cm shorter.
The standard 1- or 2-gang metal boxes here come in depths of 16, 25, 35 and 47mm.
16 is usable only for light switches with just one or two 1.0 or 1.5 T&E cables. 25mm is regarded as the norm for most other fittings such as sockets, fused spurs, and so on, although personally I prefer 35 wherever possible. 47mm is generally used for things like stove and shower isolators where you need to run 6mm or larger cables.
The main incompatibility problem with these is when fitting replacement new accessories to pre-1970-ish boxes, since the new mounting bolts are a 3.5mm metric thread while the old ones are 4BA (which look practically identical, but aren't).
Surface mounting boxes tend to be more an issue when it comes to aesthetics, trying to match up square corners versus rounded corners, etc.