Back box question URGENT

[andemz]

Hi all,

If i am having a 3 gang lighting switch will operate 2 way. How big is the back box to be a single or a double.

The bloke in the lighting shop said that 1 gang would be adequate. With 6 cables going into a 1 gang with the grommits on looks impossible.

Would you go for a double backbox like this.

I am chasing out tomorrow see.

 

[andy]

The bloke in the lighting shop said that 1 gang would be adequate.

nuff said

 

[andemz]

I must add that the lighting cable is 1.5mm2

so 3 x 1.5mm2 and 3x 1.5mm2 of 3 core

The 3 gang light will be dimmers so a 3 gang dimmer and when i went onto to TLC they put a 2 gang as a related item and not a 1 gang back box.

I'm just wanting to clarify a point.

 

[andy]

depends on the size of the switch. if its designed to go in a single box, then there is no point in puttin a double box in since ull just have to change it. make sure you know what size it needs first

 

[andemz]

Mmmm I've had a good look on the tlc website and a lot of the 3 gang dimmers are showing a double back box as a related item and not a single backbox.

My plan is to have 3 x 2 way switching in my living room. The one switch near the door entrance will be a normal 3 gang switch 2 way and the other will be a 3 gang dimmer.

My plan therefore will be to have a double backbox for the dimmer and a single back box for the normal switch

 

[TexMex]

As, has been pointed out already, wether you get a single or double gang back box, would depend on the patress that you are using.

I would suggest, however, that you use a deeper box than the one you have depicted. Although you can do the job with a 25mm back box, you will have to be very neat with your cabling to get the patress back in place with all those cables behind. It would be far easier if you use a 35mm, or perhaps even a 47mm deep jobbie.

 

[andy]

I would suggest, however, that you use a deeper box than the one you have depicted. Although you can do the job with a 25mm back box, you will have to be very neat with your cabling to get the patress back in place with all those cables behind. It would be far easier if you use a 35mm, or perhaps even a 47mm deep jobbie.

i wouldnt like to have to put all those wires in a standard 16mm box...

 

[dingbat]

Jeez! A three gang dimmer needs a two-gang back box- same size as for a twin socket-outlet. A standard 25mm back box will give you more than enough space for what you want. Just make sure that the dimmer you buy is capable of handling the load you subject it to.

 

[Lectrician]

I would go double 35mm - dimmers take up a lot of back space.

ALL 3 gang dimmers fit a DOUBLE box. All normal 3 gang plate switches fit a SINGLE box, unless you build them up out of grid (MK for example).

A 'pattress' is a surface box used when you donot wich to flush a box in, not the plate that forms the switch or socket.

 

[TexMex]

A 'pattress' is a surface box used when you donot wich to flush a box in, not the plate that forms the switch or socket.

But it rhymes with mattress, and I was very tired when I posted that.

 

[alertelec]

These are the back boxes that you require:

1g1/2w switch: 1g 16mm
2g2w switch: 1g 16mm
3g2w switch: 1g 16/25mm may give more room
4g2w switch: 2g 25mm
6g2w switch: 2g 25mm

1g dimmer: 1g 25mm
2g dimmer: 1g 25mm
3g dimmer: 2g 25/35mm
4g dimmer: 2g 25/35mm

In very rare cases there are 3g switches that take a 2g plate size but this RARE. Patresses are surface, backboxes are recessed. Its not personal preference, this is what matches what.

With 1.5mm T&E you will have sufficient room to wire a 3g2w dimmer with a 2g 35mm galv backbox.

 

[andemz]

Thankyou all very much i will go double back box for a 3 gang dimmer 35 mm and sinlge back box for 3 gang switch 25 mm.

That has cleared things up nicely.

 

[securespark]

Just to add that some dimmer mfrs recommend a deeper box if the rating is higher than normal so as to allow for efficient cooling. If in doubt, contact the dimmer mfrs!