Back boxes

22 Feb 2007
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United Kingdom
I am chasing my back boxes into the wall so the sockets are flush.

What do most electricians use 25mm or 35mm ?
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Depends on the type of socket / switch that you are going to, or could, use in the future. If you are using flat plate switches & sockets then the switches will need 25mm backboxes and the sockets will need 35mm. Otherwise for normal switches & sockets you can get away with 16mm and 25mm respectively except for dimmer switches which will need at least 25mm boxes.
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As one of our respected sparks Markie :eek: :LOL: has said 25mm is OK for sockets. You can sink a 25mm box in a bit deeper if you want another 5mm or so.
But it is a valid point about flatplate accessories & indeed the cable you wire in can affect the box depth too.

Back in my apprentice days, MK sockets needed two different box depths depending on the thickness of the plate. The "thin plate" socket needed 35mm & the "thick plate" needed 25mm.

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