Cable size

[hightower]

My brother wants his garage light converting to 2 way. It's currently wired 1 way in 1.5mm - for the 3 core to convert it is it permissable to wire in 1mm or does it also need to be wired in 1.5mm to match the existing wiring. 1mm will be able to cope with the current demands, just didn't know whether it was permissable to use smaller cable when 1.5 used for the rest of the wiring.

 

[davesparks]

The conductor size needs to be suitably sized for the ocpd. So assuming it's a 6A mcb then it is almost certainly fine to use 1.0mm 3core

 

[Hellmooth]

Why 1mm?

 

[hightower]

Why 1mm?

Frankly because that's what screwfix stock in 10m lengths.

So it's OK even though the rest of the circuit is 1.5 so long as it's suitable for the ocpd? I just want sure whether you could mix cable sizes halfway through a circuit, or on the switch cables in this case.

 

[davesparks]

To be honest it's a bit of a bone of contention.
It is not entirely unheard of to see circuits wired with 1.5mm feeds and 1.0mm switch drops, or 1.5mm twin used with 1.0mm 3core as a new installation.
Many of us don't agree with the practice of mixing cable sizes in s new circuit like that, but it is not forbidden.

The bottom line is that compliance with the regulations only requires that cable and ocpd coordinate and are appropriate for the load.

 

[APE37]

I personally don't like to mix sizes on lighting circuits, but at the same time I don't see it being a problem. The cpc is the same in 1 mm and 1.5mm T&E and as long as the live conductors are suitably sized for ocpd and load it is switching. I would say crack on with it.
merry Xmas to you.
regards
APE

 

[hightower]

I think I'll just invest in the 50m of 1.5mm - I'm sure it'll get used sooner or later.

Thanks for your comments guys, much appreciated.

 

[davesparks]

I wouldn't bother, I only keep 1mm on the van and have never yet worried about extending or altering a 6A 1.5mm circuit using it. 10A circuit I'll think about a bit harder and use 1.5 if needed

 

[richy3333]

Wouldn't the OP just keep 1.0 or 1.5mm as stock on his van or is he employed?

 

[Pete999]

The conductor size needs to be suitably sized for the ocpd. So assuming it's a 6A mcb then it is almost certainly fine to use 1.0mm 3core

What he said

 

[hightower]

Wouldn't the OP just keep 1.0 or 1.5mm as stock on his van or is he employed?

I'm just a trainee so don't have a van full of gear.

 

[mattg4321]

I'd go with 1mm too. In reality we all know this is going to be more than adequate in this instance.

Makes me laugh when I still see people wiring domestic lighting circuits in 1.5mm and then fitting about 20x 7 watt downlights on it.

 

[Guest77]

My brother wants his garage light converting to 2 way. It's currently wired 1 way in 1.5mm - for the 3 core to convert it is it permissable to wire in 1mm or does it also need to be wired in 1.5mm to match the existing wiring. 1mm will be able to cope with the current demands, just didn't know whether it was permissable to use smaller cable when 1.5 used for the rest of the wiring.

The only issue could be connecting a 1mm2 with a 1.5mm2 in the same terminal, the smaller core could become loose or even may not be clamped tight, that said if the cores are bent over then there should be no issue, as Davespark mentioned the OCPD if 6 amp makes it no real issue.

 

[uksparks]

I mix both sizes all the time on old installs.

ill be honest I never use 1.5mm any more, it's so much easier getting a load of 1mm twins in a back box. I used to hate people who used 1.0mm as it snapped easier, but now love it.

as others say, a 6A OCPD will be fine with 1mm

 

[Spoon]

I don't have the regs on me at the mo, but there is a section in there about minimum cable sizes for lights and power. I will try and find it somewhere. Just make sure 1.0mm is fine for lights.