Quick question about back boxes and running cables

17 Aug 2008
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United Kingdom

New extension shell complete, internal walls are cncrete 7n blocks. Inended to dot and dab with PB then skim coat.

I am going to sink back boxes for the electrician to save a bit of money but I am unsure how much i need to sink them by and what he will do with the cable.

Was assuming allow about 10mm for dabs and then thickness of pb and then sink the boxes by depth of box minus pb and 10mm for dabs? Would that be right or should I go a bit deeper just in case?

Also interested in what is standard practice for the professionals regarding running of the cables to these, will they just be attached to the wall and run in the gap behind the pb (i.e. the gap that the dabs create. I am going to pb myself so can put it on after the spark has done the fixing if that's better.

What would the pro's on here usually do? Its only single storey extension. I realize conduit may allow cables to be pulled through later? but if possible want to avoid as much chasing as possible as the extension breaks into existing house and dust goes everywhere.

Thanks in advance.
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Dot and dab plus plasterboard = 23 + 2mm for skim = depth of backboxes for all light switches and sockets.
Only need to dig in for the likes of cooker switch and or cooker connection unit which is normally 35/45mm deep or other larger cable sizes.
Cables can be clipped direct and dot and dab around them but they must run in the safe zones.
Many thanks Riveralt.

And yes aware of the safe zones thanks. Wont be cabling myself anyway but the position of the boxes has taken into account where the spark can run the cable from beneath the floor vertically to the socket, switch etc.

Much obliged.
That'll be fine for 25mm backboxes, but if you're planning on having the flat plate sockets and switches, they'll sit in better if you have a deeper box, so a 35mm box chased in by 10mm
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This may not apply if it's your own house and you are there all day - but it is always a good idea to keep a record of exactly where the various boxes are including measurements from the floor / ceiling / walls.

Some plastering people might accidentally forget to cut holes on the board or mistakenly plaster right over the backboxes, concealing them from view.
I would always use 35mm boxes for sockets now, had lots of issues with cable entry using 25mm ones.

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