Mounting Boxes

[electricryan]

I'm going to be installing a lighting switch and a few sockets around the house, what size of mounting box do you recommend I use for the switch and the sockets?

 

[Inspector]

These come in standard sizes from an electrical wholesaler. The type I assume you'll need are single or double recessed metal (for block walls) or moulded plastic (for stud walls - they sandwich the stud wall between the back box and light switch / socket).

 

[Big_Spark]

I'm wondering if he is also asking about the depth of box to use as well?

Standard depth switch and socket boxes, single or double gang, are 25mm deep, and usually sufficient for 90% of needs.

However there are two other depths, 35mm and 47mm, but you should not need these in a domestic installation.

 

[electricryan]

What about the 16mm boxes, are they not used anymore?

 

[Big_Spark]

What about the 16mm boxes, are they not used anymore?

They are, but have you even tried to mount a decent dimmer switch on one..talk about a pain in the nether regions

 

[securespark]

here here, FWL.

My heart sinks when a customer says "can you just install a dimmer for me?"

Arrrrrrrrghhhhhh!

 

[evdama]

if the installation was really "clever" you could then have a triple gang 2 way switch.Thats a red and black/red and a red ,blue and yellow (and the two earths of course) all triplicated So theres 21 wires to go into your 16mm box.
Make sure its a cheap and nasty switch with small tunnels to make it more amusing and some of the wires should be cut a half inch too short to start with.
A headache or stiff neck is always a good start too.(well,youll have one or the other by the time youve finished.)
Lets do it all in 1.5mm as well.......

 

[AdamW]

Lets do it all in 1.5mm as well.......

Sounds like you've been there before evdama!

One thing though, I always do anything lighting in 1.5mm cable partly because I thought it is best practice to use the same sized cable all through one circuit. Do you recommend using 1.0mm to the switch then?

I realise being a switch it is unlikely to be carrying the full load of the lighting circuit (unless you are lighting an operating theatre perhaps).

 

[plugwash]

i did here of one sparky who always used 1.5 for the cuircuit cable and 1.0 for the switch cable so he could easilly see which of the wires he pused into the lampholder was the switch cable

 

[evdama]

Dependant on the length of cable run and of course load,but for the accepted maximum of 12 lamps per breaker and a domestic residence situation, then 1.5 for the supply and 1.0 for the switching is fine.

Identification is simple as you could easily tag each wire with written labels or colour coded insulation tape ,or as I have done, use normal red/black for supply and a red/red for the switch.The 2way cable is easily identified by its 4 wires anyway.

Sparkies will often just wire everything in 1.5 red/black because they buy it by the mile or light-year rather than in 50m reels like us mere mortals.
Really good sparkies wire the sockets in 2.5 though

 

[securespark]

And some less good ones wire lighting in 25...

 

[evdama]

We once had a 2bed victorian terraced place with the cellar light done in crumbly 12v bell wire stuck to the joists with rusty drawing pins.

 

[Big_Spark]

Most electricians only use black/red cored 1.5 because red/red cored 1.5 is horrendously expensive in comparison. The black core should always be sleeved in red LSF sleeving.

I have not installed 1.0mm T&E in about 15 years. If it doesn't warrant 2.5mm, then I always use 1.5mm, whether it be T&E, SWA, Singles or Pyro.

The exception being the use of flexs for certain things