Let's see if I can start a friendly flame war:
Should mounting boxes be round like the European, square like the British or rectangular like the American?
Square, but deep, unless the fitting is expected to contain some if volume of the box. Also, separate devices and covers, like American, may be go so far as to have a bare
device, which a custom toggle, knob, or plate is attached (but in a way that it is relatively safe without the plate or toggle.)
I also vote for deep & square.
We use square boxes in the USA also, with mud rings (a sort of frame tht bolts on the box) for one gang or two gang. It gives you more room for wires inside the box.
The device boxes in my apartment are all square, with one-gang mudrings.
I'll give my wife's answer to such a question:
Should mounting boxes be round like the European, square like the British or rectangular like the American?
It seems there is consensus on deep and square. Now, it just so happens that I was going to suggest a new deep and square standard (for Europe only). I it seemed like a good idea, but thought you might disagree.
How about a 70x70 mm box, 60 mm between screws, screws something like M3 or M4, gangable with 70 mm between the center of boxes? (I think both British and Continetal devices will fit into it, so there will be no changeover)
The thing is that the continental (round) boxes can be ganged with 70 mm between the centers. This means there are a lot of devices that fit into combination frames for this distance. Now, the single frames are usually square and the combination frames are always rectangular. The metal frame of the devices are square too. A square box offers more space than the round.
How deep shall we make it?
A deep box offers more space and any device can be fitted. What are the drawbacks with a deep box? Only Britain (and Ireland?) seems to use the shallow boxes.
The Swedish boxes are some 40 mm deep. American boxes are - was I told in another thread - 1 1/2 inch (38 mm) or more. How about the Belgian and Austrian boxes?
Would 40 mm be a suitable depth or is 50 mm better?
We generally use very similar, if not the exact same, boxes as the UK but deep ones are available.
Round boxes were quite common here in the past for switches (tumbler) and sockets (schuko) both surface and flush
A british box isn't THAT thin.
It's also worth noting that electric boxes are designed to fit into plasterwork rather than plasterwork being designed to fit deep boxes.
The current system used here is generally fine. You shouldn't be making complicated junctions behind switches anyway! and I've never come across a dimmer or other device that sticks out too far.
Square or rectangular, and deep.
One of my complaints about the boxes typically used in British installations is that they're not really deep enough.
The 16mm box might be just about acceptable for a single switch with a single cable entering, but that's about all. I've seen triple 3-ways crammed into boxes this shallow, and 5/8" just isn't enough room for all the wiring.
The common 25mm box used for sockets is barely big enough for two sets of 2.5 T&E cables on a ring or radial circuit.
I'd like to see deeper boxes specified as certain minimums, although the construction of walls in this country poses a small problem. While we're at it, I'd like to see timber used a lot more instead of brick.