What size cable do you use for new lighting circuits?

[Calebp43]

So im a third year apprentice and should be qualified next year (whoopee). One thing has always made me curious and that is what cable size should we be using to rewire or in a new build for lighting in 2021? OF COURSE this depends on the load and how it's installed etc but in general what size cable would you use?
Out of the three people I worked with only one of them used 1mm. I kind of levitate towards that side as well and I'll explain why right now -
1mm cable can handle 8amps when surrounded all sides with thick insulation. That's 8x230 so 1804 Watts. 16amps clipped direct, that's 3680 watts. If anything we are all gonna be seeing more and more LED's with low power consumption and even if we don't... Well we could still have 26, 70 watt bulbs in one circuit if the cable is surrounded in insulation... Which it rarely is. Usually it's ran on top of the insulation anyway. That doubles too 52 when clipped direct! I know the price difference isn't that much but it all adds up.
I would love to know the cable size you qualified electricians use and maybe if you have time a little comment explaining why. Like I said I should be qualified next year and want to evaluate everyone's opinions before I go ahead and make my own decisions in the future.

 

[nicebutdim]

Good point! The assumption that I (and probable most) made was the poll was about domestic lights.

I'd guessed it did relate to domestic, but added that comment as a response to points raised in the quoted post.

 

[SJD]

Since I've not seen it mentioned (domestic context), how about 1.5mm2 feed from the consumer unit to one light switch to the next. Then 1.0mm2 from each switch to the light(s). And none of this loop in at the lights nonsense!

 

[brianmoooore]

Since I've not seen it mentioned (domestic context), how about 1.5mm2 feed from the consumer unit to one light switch to the next. Then 1.0mm2 from each switch to the light(s). And none of this loop in at the lights nonsense!

You haven't read post 18, then.
It all depends on the calculations. I use 1.5 if it helps meet the regs, but otherwise 1.0,

 

[nicebutdim]

Since I've not seen it mentioned (domestic context), how about 1.5mm2 feed from the consumer unit to one light switch to the next. Then 1.0mm2 from each switch to the light(s). And none of this loop in at the lights nonsense!

Funnily enough I do see similar in NI - 1.5mm from one point to the next, with switch cables in 1mm. I think this house was done that way, but looped at lights.

 

[SJD]

You haven't read post 18, then.
It all depends on the calculations. I use 1.5 if it helps meet the regs, but otherwise 1.0,

Sorry, I'd missed that post. I've done this on a couple of large domestic new builds (3-storey mansion, CUs in basement plant rooms). I've quite got to like it even for more normal sized houses, and indeed it does mean you always know the feed in/out at a switch, though I'm sure someone will tell me I'm contributing to the rise in copper prices.

 

[brianmoooore]

Feed in and out at switch is the new normal way of wiring lights, if just one or so lights per room on a single switch point. Where things get more complicated, I favour the multi way junction box, fitted somewhere reasonably accessible, with sometimes as many as 20 cables coming to it.
Nothing to do with 1.0 or 1.5 though.

 

[ian.settle1]

Most lighting circuits I work on are 1.5 or occasionally 2.5mm

When I was at college many years ago one of the other apprentices told us that an electrician he worked with said when he wired lighting the minimum size was 2.5mm and sockets 4mm

 

[SJD]

When I was at college many years ago one of the other apprentices told us that an electrician he worked with said when he wired lighting the minimum size was 2.5mm and sockets 4mm

Lights in 2.5mm2 - are you sure this electrician wasn't really a builder?

 

[MJPD29]

1.5mm every single time. 1mm twin and earth is extremely rare in the north of Ireland and I'm yet to come across a property wired in it. Most wholesalers don't even stock it because no one buys it. Commercial and industrial applications I've used up to 10mm and street lighting applications 16mm.

 

[Pretty Mouth]

1mm for me, unless I'm wiring a palace.

• Cheaper
• Thinner, so can cram more into a busy backbox
• Easier to terminate: You get some tiny terminals on things these days - dimmer modules being a prime example. Getting more than 1 X 1.5mm in them can be impossible.

 

[LukeD]

1mm for me, unless I'm wiring a palace.

• Cheaper
• Thinner, so can cram more into a busy backbox
• Easier to terminate: You get some tiny terminals on things these days - dimmer modules being a prime example. Getting more than 1 X 1.5mm in them can be impossible.

THis is a issue .. terminal sizes are rubbish now

 

[UNG]

I hate fault finding on a lighting circuit wired in 1mm² cable you invariably end up spending more time fixing broken / snapped cables than finding the fault
Another argument for using 1.5mm² especially on the upstairs lighting is that it is quite often used to supply the aerial amp in the loft, although some of the newer aerial amps can be supplied though the co-ax using an inline power injector from a socket behind the TV