Ring circuit and pattress Boxes

Having just had a partial damp course installed, I am taking advantage of the pause before the plasterers arrive to replace the rather old and dubious radial circuit that provides power to downstairs in our house with ring cicuit. Although I am happy with the details of the wiring itself, I am looking for advice on the type of pattress box to use. The choice seems to be plastic boxes that only have punch-outs for the cables at the rear or metal boxes with punch outs at the rear, sides, bottom and top. The plastic ones seem preferable as they do not have to be lined up exactly with the level of the (future) plaster but they are awkward to install because the cable has to enter from the back. Is there a reason why plastic boxes with cable entry at the bottom are not available? Could I just drill holes in the bottom of the boxes?
Thanks for any help
Martin
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The plastic boxes are for surface mounting (although metal surface mount are also available). The metal boxes are for burying in walls. You appear to want the metal ones.

Eh? I don't understand. Metal flush boxes do not need to be accurately lined up with the plaster. You'll notice that the accessories will even screw down until the metal box is well inside the level of the back face. It is intended that the accessory actually tightens against the plaster wall, rather than the box.
Christian.
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These sound like dry lining boxes - designed to be fitted in plasterboard, etc.

But dry lined boxes have a lip at the top which is designed to sit against the surface - anything else would look odd. Normal surface mount plastic boxes have side entries and I suppose wouldn't look that bad if they stuck out a bit, but your plasterer won't thank you for them.

The correct way would be to use metal boxes and sink them below the eventual level of the plaster. Leave the wires sticking out so you can find them again when the plasterer fills them in. ;-) You might also need longer screws if the brickwork is very uneven.
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Dave Plowman wrote:

Any fit the cable hole with a rubber grommet, a box of 100 does not cost much.
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Toby.

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If the plaster is off the walls, then go for metal back boxes straight to the brickwork, and leave the sockets off until the plasterer has done his thing. Then you can make the socket plates fit flush on top the new plaster because the spread will have taken the gunk right up to the edges of the new boxes.
You might find that the white surface boxes are to deep for the new plaster, so you'll be left with the sockets sticking out from the wall.
If the radial circuit is using 2.5mm csa' cable, then all you'll need to do is extend one end of it back to your consumer unit (fuse box). That way you don't have to remove any of the existing cable, just find the end where the circuit stops and add on to it.
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Buried in plaster you should be using the galv steel boxes. They are set to be just at or below the finished plaster depth. Good ones will have one of the face plate fixing lugs adjustable so you can get your sockets dead level. (I hope I'm not the only one who uses a spirit level when finally fixing accessories ;-)
Unless your brickwork is rock hard, I'd also recommend the 35mm deep versions over the 25mm ones. The extra depth makes final wiring a lot easier. Don't forget to grommet the cable holes.
Depending on your situation, also consider just fitting 20mm oval conduit for now, your can then run in the cables after the plaster work has been done. Depends on you arrangment with underfloor access etc. Don't expect to get more than one 2.5mm T&E in each conduit, so you'll need two drops from each pattress.
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Steven Briggs



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