Size Backbox to use

[mojowaky]

Hi everyone,

Im not a very experienced sparky.
Im looking to replace several 2 gang 13A double sockets through out a house.
They are all surface mounted plastic pattress boxes on the walls.
Im looking to chisel the walls and have metal backboxes inside the walls.
I have no experience with chiseling and inserting metal backboxes in anything but plasterboard.
Im not sure whether to pick 25mm or 35mm metal backboxes.
The walls I need to work on range from about 75mm to about 90mm in total depth and are all solid walls (no plasterboard), Im pretty sure almost all are brick wall, I know for sure some are as there is building work going on and some walls are exposed in the edges.
I would prefer to use 25mm backbox throughout so I got enough space to put the box in and drill deeper to put in the drill holes for the plastic wallplugs to hold the retaining screws to hold the backbox in.
Question is do you think 25mm would be enough for electrical sockets bearing in mind they would of course have the standard 2.5mm cable and its likely there would be 2-3 sets of cable maybe even 4 ? Do I think I could I get away with 25mm backboxes, at the moment as the current plastic surface mounted patresses are 35mm, as I dont like the idea of using 35mm boxes ?
Also the building regs only let you chisel in to 1/6 of the depth for channels (cant remember if that was horizonal or vertical), does that mean you cant chisel more than 1/6 of the depth for the backbox as well or that does not apply ?

Thanks



Mohamed

 

[malcolmsanford]

Welcome to the Forum Mohammed or As-Salāmu `Alaykum

Well mate the old rule of thumb is, engineering bricks 25mm is more than enough, soft breeze whatever is lieing around in the van.

Seriously 25mm back boxes for sockets are normally more than enough, though a bit unclear when you say you can have 4 sets of cables in to a point, why would you have that many, on a conventional ring circuit or radial there are just 2 sets .

 

[DurhamSparky]

47mm back boxes....!!!

get the hammer and chisel out!

 

[SirKit Breaker]

47mm back boxes....!!!

get the hammer and chisel out!

You rotten *******

 

[telectrix]

47mm????? what you wiring in, 10mm? 25mm and sink 1/4" below finished plaster level. plenty.

 

[DurhamSparky]

i want him to work hard and get in to a sweat!

 

[ringer]

25mm backboxes should be fine. And yes, the recommendation re depth of chases relates only to channels. You can go deeper for individual points such as socket outlets and light switches.

 

[Rockingit]

47mm????? what you wiring in, 10mm? 25mm and sink 1/4" below finished plaster level. plenty.

I just love the assumptions made that everyone works in imperial and metric measurements fluently!! Only teasing, but you gotta admit.....

 

[telectrix]

i only use them foreign measurements when stuff is supplied, described in mm., like cable. hate metric. it'was a system devised by the french after they'd chopped the heads off everyone that could count past 10.

 

[Rockingit]

Tel, there's some thinking that you just can't fathom....... :joker:

 

[telectrix]

fathom, 6 feet.

11 fathoms = 1 chain. 10 chains = 1 furlong. back to the horses.

 

[Guest123]

25mm will suffice as long as you aren't planning on using flat pate accessories on 2nd fix.

 

[sedgy34]

47mm back boxes....!!!

Get the hammer and chisel out!

i agree 47mm boxes

 

[Lucas]

I'd fit 35mm just through personal prefrence. The extra 10mm is worth it in my eyes.

 

[Amp David]

I'd chase to 35mm then fit 25mm they're slightly cheaper:joker: