1mm or 1.5mm for all internal light runs ?

[Dustydazzler]

I guess in the older days of 1 lighting circuit for the entire property with say 15 x 100w bulbs on it then 1.5 for the circuit might have been better

but in 99.9% of modern builds you have at least 2 designated lighting circuits with minimal loading on each so 1.0 is absolutely fine

i honestly don’t know why people waste 1.5 on domestic lighting

 

[123]

I guess in the older days of 1 lighting circuit for the entire property with say 15 x 100w bulbs on it then 1.5 for the circuit might have been better

but in 99.9% of modern builds you have at least 2 designated lighting circuits with minimal loading on each so 1.0 is absolutely fine

i honestly don’t know why people waste 1.5 on domestic lighting

In these parts most (if not all) wholesalers don't stock 1.0mm T&E, 1.5mm is generally used for lighting & heating

 

[LastManOnline]

In these parts most (if not all) wholesalers don't stock 1.0mm T&E, 1.5mm is generally used for lighting & heating

I have never seen a coil of 1.0mm T&E. I am obliged to use 1.5mm here in ROI. However I am surprised that in NI you don't use 1.0mm as you are under UK regs.
I do agree though that 1.0mm is adequate, particularly with the advent of leds,and that the UK is correct in its approach. Gone are the days when a homeowner would have at least two, possibly three 500watt halogen security lights outside his house.

 

[pc1966]

In these parts most (if not all) wholesalers don't stock 1.0mm T&E, 1.5mm is generally used for lighting & heating

That is odd, maybe it is for ease of stock in both UK and ROI rules by the companies.

I can see some sense in stocking 1.5mm for the odd 16A radial circuit and its dual-use for lighting, but for many case I would just opt to use some 2.5mm in those cases as common with the usual RFC used here. Off hand I don't see a lot of 16A radials in use, odd immersion heater, maybe dedicated feed to a boiler or freezer?

However, it also seems odd the ROI does not permit 1mm for lighting like the UK does.

 

[nicebutdim]

In these parts most (if not all) wholesalers don't stock 1.0mm T&E, 1.5mm is generally used for lighting & heating

1.5 is all I've ever seen used for lighting over here, but oddly enough I spotted 1mm as strapper when finally righting the 2 way switch beside me, that was wired upside down. I don't have a great deal of experience in such matters, but it struck me as being unusual.

 

[LastManOnline]

However, it also seems odd the ROI does not permit 1mm for lighting like the UK does.

There are no electrical reasons why it should, nt be permitted. Is it a major issue?... No. But there are times, such as when doing rewires and space in older conduits is very very tight, that a smaller size T&E can make a world of a difference.
That said I have also made good use of a 1.5mm lighting circuit on a 10 amp mcb on occasion whereby small items of electrical equipment could be connected to same circuit (provided they are under 300 watt)