Back box / Chasing

[morg]

Hi, looking for some guidance please,

I plan to install the back boxes and cutting out the chases in prep for the electrician - Complete re-wire, new CU etc etc, I'll be plastering over the cables as well.

Just wondering what's the preference these days, do we install 2 x 2.5mm T+E in the same 25mm KO - Or separate 20mm KO for each cable?

Internal wall 100mm, plan to use 35mm back boxes.

My gut feeling says they didn't provide the 25mm KO for nothing, but just thought I'd seek some advice thanks

 

[sparkwright]

NORMALLY, I would use one 20mm grommetted hole to accommodate two 2.5mm2 T+E cables.

 

[morg]

Great thanks for the help!

But ideally what would be preference from an electrician point of view?

as I'm doing the donkey work, want to make it easier for the sparky

 

[EFLImpudence]

Why are your cables only coming from above?

Surely most will be one each side - making your question unnecessary.

 

[morg]

Why are your cables only coming from above?

Surely most will be one each side - making your question unnecessary.

CU / Meter on ground floor.

Ground floor sockets and light switch cables will drop down from ceiling joists (ceiling plasterboard removed and joists are exposed on ground floor)

1st floor sockets would be bottom entry or side, light switch cables would drop down from attic.

Thanks for the help

 

[EFLImpudence]

CU / Meter on ground floor.

Errr - yes.

Ground floor sockets and light switch cables will drop down from ceiling joists

That sounds like an awful waste of cable for the sockets. Not all sockets need to do that.
Cannot the cable drop down once, then be installed horizontally around the room(s) until the last rises to the ceiling?

1st floor sockets would be bottom entry

Ok, but depending on the height the same applies in reverse.

or side,

Do you mean you will be doing what I am suggesting?

light switch cables would drop down from attic.

First floor, yes - but light switch cable drops are only one cable.

 

[morg]

Good point EFL many thanks

Yes, definitely we can do what you suggest - cutting some of the chases horizontally on the ground floor makes total sense.

On the first floor, sockets would be approx 450mm up from finished floor - So probably stick to vertical chases on all these sockets.

Thank you for the advice

 

[sparkwright]

Great thanks for the help!

But ideally what would be preference from an electrician point of view?

as I'm doing the donkey work, want to make it easier for the sparky

As I said - 2 2.5mm2 cables through one 20mm hole.

Reason? He is more likely to have 20mm grommets. And by using one hole, it will all line up with narrower chases, and 20mm oval conduit or 25mm capping.

Anything else, for me at least, would be more 'awkward'.

 

[morg]

Thanks for the help sparkwright

Will follow the advice given cheers

 

[chivers67]

Personally I'd Install deeper back boxes, 35mm as you won't be limited in the accessories you choose such as USB sockets or similar.

 

[chivers67]

I'd use deeper back boxes where ever you can so you're not limited on the depth of the accessories. The 25mm knockout is for larger cables - cooker for instance.

 

[ebee]

I tend to put 2 x 2.5 T & E cables thru the same hole if fed vertically and usually a middle hole at that - some metal boxes have three holes on the long surface and some have four. If I`m installing a ring final then often the two cables in one hole might be for the ring and the other hole (with one cable in it) might be for the spur. It sometimes aids identification (although I do tend to avoid spurs on new circuits and perhaps consider spurring only for later additions).

I usually use 25mm back boxes although with USB sockets etc there is a good reason for 35mmm boxes - for light switches , even 1 gang 1 way, I`d still use 25mm min and never 16mm, 16 is too cramped for wiring, especially if it might be altered in future or a traditional dimmer switch substituted - there again, for dimmers 35mm would be preferable