socket box depth

[JohnW2]

Come on John; sometimes I wonder. ... Mentioning that it would increase the Zs was apparently a foolish thing to include.

As I said, I agree with virtually everything you wrote, but genuinely don't fully understand your comment about Zs, at least as a generalisation. Sure, if one uses some spurs, then the ring itself will be shorter, hence sockets etc. 'on the ring' will have a lower Zs (as compared with the situation with everything 'on the ring'). However, that has to be balanced against the fact that those sockets which are on spurs may well have a higher Zs than they would have done if on the ring.

FWIW, I certainly don't personally subscribe to the view that it is 'wrong' (at least, 'bad practice') to design a ring final with spurs.

Kind Regards, John

 

[EFLImpudence]

However, that has to be balanced against the fact that those sockets which are on spurs may well have a higher Zs than they would have done if on the ring.

Not if there are several such spurs and consequently a considerably shorter ring.

FWIW, I certainly don't personally subscribe to the view that it is 'wrong' (at least, 'bad practice') to design a ring final with spurs.

It is obviously not, but some people say it would be better with all sockets on the ring - just in case; it wouldn't.


Not to scale.

 

[JohnW2]

FWIW, I certainly don't personally subscribe to the view that it is 'wrong' (at least, 'bad practice') to design a ring final with spurs.

It is obviously not, but some people say it would be better with all sockets on the ring - just in case; it wouldn't. <diagram of ring arrangement, with and without spurs>

It may not be possible/practicable/efficient in terms of cable routing, but if that is not a problem, it is often possible to modify the topology of a ring such that having everything 'on the ring' uses little/no more (maybe even less) cable than does your arrangement with multiple spurs - see red lines added to your diagram:

Kind Regards, John

 

[EFLImpudence]

No. That's not possible. Several separate rooms.

I wouldn't have been daft enough to spur sockets which would be better on the ring.

I did say it was not to scale and, of course, the sockets are not on the floor.



I think you are taking my original statement a little too far,

 

[JohnW2]

No. That's not possible. Several separate rooms.

OK - but unless you show me where the room boundaries are, I can't consider whether there might be a viable 'all on the ring' option! Mind you, the fact that sockets are not all in the same room does not necessarily preclude a ring which 'jumps between rooms' (if they are adjacent, horizontally or vertically)!

Kind Regards, John

 

[EFLImpudence]

It doesn't really matter.

Whatever you do, and even what you have drawn (red line), will lengthen the ring, won't it?
I agree that this may not matter but that is the point I am making.


Ok. so the whole diagram is one kitchen, the top and bottom lines are above worktop ring and the spurs are appliance below.
However the two centre sockets, on horizontal spurs, are actually in rooms to the left and right (drawn like that for ease).

 

[deadshort]

There must be an awful lot of unnecessary work carried out.

In the time you have debated i could have fitted a 47mm box in granite

DS

 

[EFLImpudence]

Yes, it turned out more complicated than I intended.

I knew what I meant.

 

[deadshort]

Well, that's all that matters !

DS

 

[flameport]

For the original question:

16mm boxes are the work of Satan and must never be installed.
25mm is fine for the majority of light switches, even flat plate dimmers.
May be desirable to have 35mm for light switches where wiring is looped at the switch box rather than the ceiling light.
35mm for all socket outlets, since it's almost inevitable someone will want to put flat plate or USB outlets in there despite them stating they only want white plastic.
Cooker switches can be fitted into 35mm boxes, but it is certainly easier with 47mm.
Shaver sockets must have 47mm.

 

[JohnW2]

Whatever you do, and even what you have drawn (red line), will lengthen the ring, won't it?

Not necessarily. When printed out on A4, my 'red line' is around 980 mm in length, in comparison with your black line (ring with multiple spurs) at about 1000 mm - i.e. virtually identical.

Ok. so the whole diagram is one kitchen, the top and bottom lines are above worktop ring and the spurs are appliance below. However the two centre sockets, on horizontal spurs, are actually in rooms to the left and right (drawn like that for ease).

Fair enough - although I would probably question the wisdom of having one circuit (of whatever configuration) supplying a kitchen (including 6 below-counter double sockets 'for appliances') plus three or four other rooms.

However, I don't think that anything is to be gained by debating details. I have already agreed with you, both explicitly and by implication, that I agree that it can be appropriate to design a ring with spurs - and I certainly agree that one should not avoid using spurs "just in case someone wants to add spurs in the future". Most of the rings in my house have had multiple spurs ever since they were first installed (and have undoubtedly gained a good few subsequently!). The only real downside I can think of is that the spurred sockets do not benefit from 'CPC redundancy', but I know that you (and probably I !) do not regard that as very important.

Kind Regards, John

 

[JohnW2]

For the original question: ... 25mm is fine for the majority of light switches, even flat plate dimmers. May be desirable to have 35mm for light switches where wiring is looped at the switch box rather than the ceiling light.

Bearing in mind that this is a DIY forum, I would be inclined to suggest to the OP that, if it's not too difficult to install, it might be worth his using a 35 mm box for his 3-gang switch - since, even without looping, there are quite a lot of cables and conductors for a DIYer to cope with in a shallower box.

Kind Regards, John

 

[Iggifer]

Shaver sockets must have 47mm.

I don't disagree obviously, as this is just a given. But invariably, you end up with the box so far back in plaster+tile+adhesive you probably could have put a 25mm in! Thank god for extension studs.

 

[seasickstevie]

Cooker switches can be fitted into 35mm boxes, but it is certainly easier with 47mm.

No doubt it's possible but personally, I wouldn't even consider a cooker switch or cooker outlet plate in anything less than a 47mm box.

Edited in accordance with JohnW's requirements

 

[JohnW2]

No doubt it's possible but personally, I would even consider a cooker switch or cooker outlet plate in anything less than a 47mm box.

I think you may wish to revisit some of the typing there!

Kind Regards, John