mixing lighting cable sizes

[Perth]

Have got 2 lights in hall coming off a multi terminal junction box.
The switch is 1 gang 1 way also coming from that junction box.
I want to add a 3rd porch light cable into the junction box and put a 2 gang switch wired from the junction box with a 3 core wire so the 3 core will operate the 2 gangs 1 way. 1 gang for hall lights and 1 gang for new porch light.

However when I came to do this having run my new cable for porch light up to the junction box I realised that the new cable seems ever so slightly thinner than the other light cables.

I assume that either the other light cable is a different brand or it is 1.5mm and I have 1.0mm.
Is it safe if I have a smaller cable size in this situation or should I change it to 1.5mm (if that is what the existing cable size is)??

How can I tell the old cable sizing ( Crompton cables 300/500V) and if it is 1.0mm or if it is 1.5mm.
All lights in house are fed from 3 multi terminal boxes (approx 6 lights on each) into which the main feed arrives and all switch cables and light cables connect and fan out from there (the feed does not continue on to another JB)

New cable is copper cable company BS 6004H I.S.201 1.0mm

Thanks

 

[Damocles]

Probably. What is the rating of whatever is protecting your lighting circuit? If 6A then certainly, if 10A then probably. You did check that extra lamps would not overload the circuit?

Although it is not a good idea to this. someone in the future may see one or other cable and assume the whole circuit is this same size, and make changes on that assumption.

Best way to check would be to look at some in a DIY shop, or buy a bit of known size to compare.

 

[Perth]

Each of the 3 JB's which each feed 6-7 lights go back to the meter and meet their own 5A fuseholder.

I will check cable size in electic shop - there is such a slight difference that I just wondered if there was a definite way of working out if you have 1.0mm or 1.5mm rather than using eye guessing.

Unless i can know for sure what the existing cable size is then either way if I guess by eye and get it wrong adding there could be a mix of 1.0mm and 1.5mm radiating from the multi terminal JB.

I'll ask at the electric supply shop and see what they think - just wanted to know if it would be a death if they are mixed!

Is it safer for feed to be 1.5mm and radiating light/switch cables to be 1.0mm
or for feed to be 1.0mm and radiating light/switches to be 1.5mm?

 

[ban-all-sheds]

I just wondered if there was a definite way of working out if you have 1.0mm or 1.5mm rather than using eye guessing.

Yup - measure the diameter of one of the conductors with a micrometer or caliper gauge with good enough resolution for you to be able to tell the difference between 1.13mm and 1.38mm.....

 

[plugwash]

There are several considerations with mixing cables on a cuircuit

The first is making sure all the cables are suitable with the protective device as it is now.

The second is the possibility someone could uprate the protective device in future without realising the presence of the smaller cable.

1.0mm is fine with your cuircuit as it is now. If someone uprates to 10A then 1.0mm is still ok provided you aren't running it through thermal insulation

protective devices over 10A are very rarely used for UK lighting cuircuits anyway.

so overall i think using the 1.0mm is fine.

 

[Perth]

should elec cables in loft be to the outside of the loft insulation?

 

[ToolbeltDandy]

As I understand it, cables are supposed to be situated above insulation. Having said that, when I was in my attic, I noticed that wasn't the case. Still, it does get hot in the attic, when the sun is out, so maybe they're actually cooler where they are? According to my insulation packaging though, cables are supposed to be re-routed and not covered.


Also, with regards to wire gauge, I've got some lighting cable here which has it's specifications stamped into the plastic sheath at regular intervals. If you can find a stretch of the cable, and shine a torch along it, perhaps you can find the specs. Or perhaps not... :/

 

[Hibbo]

As I understand it, cables are supposed to be situated above insulation. Having said that, when I was in my attic, I noticed that wasn't the case. Still, it does get hot in the attic, when the sun is out, so maybe they're actually cooler where they are? According to my insulation packaging though, cables are supposed to be re-routed and not covered.


Also, with regards to wire gauge, I've got some lighting cable here which has it's specifications stamped into the plastic sheath at regular intervals. If you can find a stretch of the cable, and shine a torch along it, perhaps you can find the specs. Or perhaps not... :/

I think the fella might have finished his wee project by now mate...

 

[Taylortwocities]

 

[ToolbeltDandy]

As I understand it, cables are supposed to be situated above insulation. Having said that, when I was in my attic, I noticed that wasn't the case. Still, it does get hot in the attic, when the sun is out, so maybe they're actually cooler where they are? According to my insulation packaging though, cables are supposed to be re-routed and not covered.


Also, with regards to wire gauge, I've got some lighting cable here which has it's specifications stamped into the plastic sheath at regular intervals. If you can find a stretch of the cable, and shine a torch along it, perhaps you can find the specs. Or perhaps not... :/

I think the fella might have finished his wee project by now mate...

I figured! but I often get information from old threads so I thought the information might be useful to someone who searches and finds this thread in the future.