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Housing - New Build: Electrical box, galv or dry lining...

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  1.  
    ...ok so only vaguley green building in that its a query about my house which is a very green building.

    We have a timber frame + non loadbearing inner frame, plasterboard lining (for fire... ask the BCO..), Intello membrane, 38x63mm battens, then later some plasterboard + skim or clay plaster depending...

    option A

    35mm metal box fixed to top of batten, board and skim over, find box again

    option B

    no box (yet), clip cables in location, board and skim over, find cables, cut hole, use plastic dry lining box

    I prefer A as I can locate the boxes and my electrician can wire into them, leaving me to do the 2nd fix and I'm always worried about wobbly dry-lining boxes but convention dictates option B...

    ...thoughts...

    J
    • CommentAuthorbarney
    • CommentTimeJun 19th 2012
     
    Fix the back box with the edge flush with the inner face of the internal plaster board (if you use 25mm boxes, then perhaps a pad of 12mm ply behind the box fixed between the battens or if you use deeper boxes, side fixed to the battens. Board over and either mark the board or smack a rough hole through it as you are fixing.

    Clean out after surface finishes with stanley knife or pad saw - second fix.

    Personally speaking, I would avoid dry lining boxes (on sockets at least) - any vigerous flex action tends to make then more than a tad wobbly

    Regards

    Barney
    • CommentAuthorfinny
    • CommentTimeJun 19th 2012
     
    As above, don't use patresses unless using a stable dry lining dense board like fermacell,
    either way, whats to gain by not installing cables and box first fix?
    • CommentAuthortony
    • CommentTimeJun 19th 2012 edited
     
    ....clip cables, fit p-board, fit plastic dry lining box, clay plaster, QED
  5.  
    Posted By: tony....clip cables, fit p-board, fit plastic dry lining box, clay plaster, QED


    Clay plaster over dry lining box...?

    J
    • CommentAuthortony
    • CommentTimeJun 19th 2012
     
    yes why not, not much different from finish plaster.
  7.  
    Ok. I can see that. The thicker clay would set the drying box more solidly that a skim,

    J
    • CommentAuthorbarney
    • CommentTimeJun 19th 2012
     
    Dry lining boxes are lipped - any plaster over that cracks off and looks awful. It's up to you, but personally i would wire and fix metal flush boxes - then finish and second fix.

    As I mentioned, a dry lining box stays in place simply due to the tightening of a 3.5mm set screw into a flimsy hinged plastic pad - it relies entirely on the strength of the raw edge of a bit of plaster board. If it was my house, I know what I'd be doing.

    regards

    Barney
  9.  
    Good to see some support for plan A, to be honest, the ability to set the box positions 1st (ie sockets where we want them not where the electrician thought best and the fact that the wiring is more advanced by the time I get to it seemed like a no brainer, its just that everyone in the trade seemed to assume I would fit drylining boxes

    (anything else being another of james wacky-architect-ideas, that'll never work, thinks he knows how to reinvent the wheel, what does he know etc etc...)

    J
    • CommentAuthorbarney
    • CommentTimeJun 19th 2012
     
    I used to be a spark - I put stuff generally where it was easier for me - not for the client. I used dry lining boxes because they are quick - which equals money when you are on a price.

    When i did my own house I used flush metal boxes, and put the stuff where it suited me or lined up nicely with such things as wall units. I put the switches at identical distances from doors (or actually the architraves). That takes time (and effort and planning) - if the spark is on a price, you'll get it quick and rough - trust me.

    Plan A is where I would go

    Regards

    Barney
    •  
      CommentAuthorSteamyTea
    • CommentTimeJun 19th 2012
     
    Don't forget that there are places that electrical stuff can go and where it cannot.
  12.  
    Don't worry, I am safe zone / part M guru...

    :wink:

    J
  13.  
    Why skim your plasterboard? Just tape and finish the joints. The galv boxes over here have indents to align them to the studs etc. so that the surface of the box will be flush with the front surface of the plasterboard - you cut out the hole as you're screwing in the board and then it's all flush when you're done.

    Paul in Montreal.
    • CommentAuthorCWatters
    • CommentTimeJun 20th 2012
     
    If you wire and fix metal back boxes, coil the wire in the back box. Then you can use the box to mark the back of the plasterboard "cookie cutter" style.. Just offer up the plasterboard and give it a thump roughly where the box is. It will leave marks on the plasterboard to show you where to cut out the hole.
  15.  
    Posted By: Paul in MontrealWhy skim your plasterboard? Just tape and finish the joints.


    Indeed, as I've specified on many commercial jobs however your average domestic plasterer seems to think this is more hocus pocus and as a result rarely do it.

    Having said that, as we are boarding the skim will cover a multitude of sins...

    J
  16.  
    Posted By: CWattersust offer up the plasterboard and give it a thump roughly where the box is. It will leave marks on the plasterboard to show you where to cut out the hole.


    Ok. so with that (and my 38mm deep battens and 12.5mm board) I guess I would use the luxurious 47mm boxes which would sit proud about 9mm in order to provide the cooker cutter cutting edge...?

    J
  17.  
    James, have you used tapered-edge boards? If so, even fairly rough joints can be filled OK. I no longer use paper tape, but use adhesive glass-fibre scrim instead, and it works well. Even on end-to-end (non-tapered) joints a bit of feathering results in a good finish. Not great if you want to go over every surface with a straight-edge, though!
    • CommentAuthorbarney
    • CommentTimeJun 20th 2012
     
    Don't put the box flush with the outer face of the board - plasterboard is incombustible and forms a perfect;y acceptable part of the enclosure

    Don't try and cut out the box before fitting the sheet

    As I said, fix the box flush with the rear of the board

    Mark and make a small hole in the board to identify the box location behind. Offer up the baord and fix in one operation - don't bother with "cookie cutter" ideas - they just waste time and effort.

    Trust me, I'd did this for a living - safe zones are fine, but you'll be having RCD protection anyway. Fixing heights for part M are flexible enough so you get what you want, excepting sockets that are at "skirting" level

    regards

    Barney
  19.  
    Posted By: Nick ParsonsNot great if you want to go over every surface with a straight-edge, though!

    Will have to check that with the QA coordinator.... ( :wink: )


    Thanks Barney, excellent advice from someone who's done it once or twice...:wink: (but appreciate the lateral thinking Colin :bigsmile:)

    J


    J
    • CommentAuthormarktime
    • CommentTimeJun 20th 2012 edited
     
    Nick, you're suggesting glass-fibre scrim, (that the adhesive mesh tape?) in place of paper tape. What made you arrive at that decision? Apologies if slightly OT.
  21.  
    Marktime, I had a number of instances of the paper tape lifting off and forming bubbles on the joints. I thought I'd try conventional skimming scrim, to see if I could get a good joint without it showing through. It's fine - never a problem.

    Nick
  22.  
    Posted By: barneyDon't put the box flush with the outer face of the board - plasterboard is incombustible and forms a perfect;y acceptable part of the enclosure


    Over here, you're "supposed" to have the box end up flush with the front of the plasterboard - there's even box extenders available for those cases where the box ends up more recessed than you'd like. That said, I can't say I've always done this, but I do try - you screw most of the plasterboard in place and then just cut around the outside of the box - they're easier to locate if they're going to end up flush anyway.



    Posted By: marktimeNick, you're suggesting glass-fibre scrim, (that the adhesive mesh tape?) in place of paper tape. What made you arrive at that decision? Apologies if slightly OT.


    I ended up making the same decision. It makes ceiling joints much easier to you as you stick the tape in place first rather than having to futz around with wetted paper tape that has a tendency to bunch up if you're too rough with the joint compound knife. And there is the propensity for it to bubble. For the 1st coat with mesh tape, you have to use a setting-type compound, rather than a drying one. Even with butt joints you can feather the compound out on each side to give a visually flat end result.

    Paul in Montreal
    • CommentAuthorjamesingram
    • CommentTimeJun 20th 2012 edited
     
    Most use scrim/mess tape for dry lining , though skimming gives a much stronger quality finish for plaster board , unless your using fermacell etc.

    I use both options , I do find PB back boxs a pain , but you can always fix them in with a bit of decorator caulk
    behind the lip to sturdy them up a bit, certainly quick and easier than Galv BB
    • CommentAuthordjh
    • CommentTimeJun 20th 2012
     
    Posted By: Nick ParsonsNot great if you want to go over every surface with a straight-edge, though!

    Or if you have wall-washing lights, presumably?

    Posted By: Paul in MontrealOver here, you're "supposed" to have the box end up flush with the front of the plasterboard

    Plaster may be incombustible, the same as metal, but it isn't an electrical conductor. So perhaps the difference in regs/common practice regarding boxes is due to some difference in the earthing requirements?
  25.  
    Posted By: djhPlaster may be incombustible, the same as metal, but it isn't an electrical conductor. So perhaps the difference in regs/common practice regarding boxes is due to some difference in the earthing requirements?


    Over here, if you use metal boxes, they have to be grounded. Obviously plastic boxes cannot be. Also over here, metal boxes are cheaper than plastic if I recall correctly and are just better in my humble opinion.

    Posted By: djhOr if you have wall-washing lights, presumably?
    That's always the acid test of a good plastering job ... when you're taping and jointing plasterboard, a "trouble light" held at a low angle will help find these problems before you're finished.

    Paul in Montreal.
    • CommentAuthorbarney
    • CommentTimeJun 20th 2012
     
    "Over here, you're "supposed" to have the box end up flush with the front of the plasterboard - there's even box extenders available for those cases where the box ends up more recessed than you'd like"

    I don't disagree Paul, except insofar as your recepticle design differs from UK pattern 13A sockets - and you also use a differing cable type (romec or similar by code from memory).

    UK national wiring codes don't make such a clear requirement - only that terminations are enclosed in ideally non combustible materials. The slightly recessed back box takes care of most of it - as i mentioned plasterboard in incombustible. If you think of it along the lines of back boxes in traditional render and set wall construction, they are rarely so acurately positiond that the finish plaster is flush with the box - it's usually deeper. Even more so with tiled wall finishes.

    regards

    Barney
  27.  
    Posted By: barneyI don't disagree Paul, except insofar as your recepticle design differs from UK pattern 13A sockets - and you also use a differing cable type (romec or similar by code from memory).


    I think the reason for the flush-with-the-surface rule here is the predominance of timber framed construction. You don't want sparks coming out of the box and hitting the studwork. Even with tiled surfaces you're supposed to add box extensions to keep things flush. Our cable is definitely different - brand name is Romex. The conductors are black for hot, white for neutral (handy for people who are colour blind) and often the outer sheath (which is nylon, not PVC) colour is used to indicate the current rating. White is the default 15A, red is 20A. Some people use blue to indicate that the circuit has an arc-fault circuit breaker etc. It's a fairly recent thing, but makes it easier to understand the wiring. Typically, over here, way more breakers are used than in the UK. My kitchen alone has 10 breakers and I think I have around 35 in total (and the panel can fit 48 single pole devices).

    Paul in Montreal.
    • CommentAuthordjh
    • CommentTimeJun 20th 2012
     
    Posted By: Paul in MontrealTypically, over here, way more breakers are used than in the UK. My kitchen alone has 10 breakers and I think I have around 35 in total (and the panel can fit 48 single pole devices).

    That difference is because we have fuses in the plugtops, I think. And ring circuits.
  29.  
    Posted By: djhThat difference is because we have fuses in the plugtops, I think. And ring circuits.
    The fuse in the plug is to protect the wire of the device, that's all :) And ring circuits provide "too much" current to be safe for the device wire (esp lamps etc - hence the 3A fuse). Most of our breakers are 15A which isn't that different from a 13A fuse. Spurs are good because it gives you more control when you're working on something - and there's been a requirement for all bedroom circuits to use arc fault circuit interrupters now for a few years - harder to do with a ring I think. As to whether AFCIs are good or not is another debate - apparently a lot of fires are started by arcs in broken device wires that are behind furniture - not enough current to trip a regular circuit breaker, but enough sparks to cause a fire. AFCIs detect this apparently.

    Paul in Montreal
    • CommentAuthorbarney
    • CommentTimeJun 20th 2012
     
    Romex - that's the stuff.

    It's a while since i had to deal with NEC codes and the like, but it's all coming back.

    I'd agree on "sparking" risks in timber frame but the 110V system will have a greater preponderence to arcing due to the higher current for the same power delivery.

    I guess you guys still haven't finally got your heads around that fantastic british invention of the "ring main" !!

    Personally i was always a fan of many more circuits to deliver the installation demand - some of the UK custom and practice for domestic wiring really doesn't stack up when yo examinie it closely

    Regards

    Barney

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