Cable size

Just carry it on in 1.5mm. Never come across 1mm SWA. Assuming you've done the volt drop calculations for that cable length obviously

You can't do any harm (apart from expense) of using a larger cable size than required. So from that viewpoint, using 1.5mm² to extend a smaller cable is fine. The chances are the original cable is 1.5 too and you're just seeing a measuring noise. Unless the cable is an old Imperial one.


However if extending a circuit, you need to consider whether the earth fault loop impedance is still in spec, and what the voltage drop will be. If you don't know what these are, nor have the equipment to measure them, then you should really get in a sparky.

As far as I'm aware there's no such thing as 1mm² SWA - the standards usually start at 1.5mm² for anything 7-strand these days.


Why would you want 1mm² anyway - there's no problems extending a circuit in a larger c.s.a. cable after all.


   - Andy.

Thanks guys.


It is hugely frustrating! Volt drop isn’t an issue I’m using 20w leds.


I’m more concerned about extending a lower rated cable, 1mm2 with a higher one of 1.5?


I can’t imagine there being any issues but if there was, and you cannot account for Murphy’s law, then technically I could draw more than the 1mm should take?


I should add that I don’t want to use 1mm but it is old circuitry from the sparky who lived here before me. 3 core, Red, blue, and yellow.


Andy

If you are that bothered, you can get the CSA from a resistance measurement, if you know the length (given the values are low for short lengths - 1mm2 is about 16 ohm per kilometre, the reliable way is to look at voltage drop on a known heavy load).

Or just chain on the new stuff in in 1,5mm2 but set the fuse or breaker to be safe even  if it was less than 1mm - i.e. less than about 10Amps. There is no rule to prevent mixed sizes in one circuit, so long as  the protection is adequate for the thinnest section.


Is it old enough to be imperial perhaps? The newer stuff  (last 20 years or so) normally has it printed on the jacket, which makes life very easy.

Much more importantly, are the cores dry and shiny and is there any evidence of damage to the armour ? if not you may need to cut back and join onto it cleanly. And, when you have it all hooked up, please verify the earthing is continuous in the armour jacket.

Mike, you’re a star!


I’ve been looking, and trying to figure this out, for so long I couldn’t see the woods for the trees.


it is a lighting circuit originally so the protection is 6a, can’t see the woods for the trees!

also, if I had an extra brain it would be lonely, lol.


thanks again, hugely appreciated.


Andy

Although the question seems well resolved, the following might help anyone else trying to identify a conductor by mechanical measurements.


Wire sizes are specified by IEC60228 in terms of electrical properties (resistance), not directly in terms of actual cross-section. With the quality of copper normal in wires nowadays, the actual cross-section is smaller than the nominal value.  Around 1.25 mm² for nominal 1.5 mm² is similar to what I've noticed.

Great response thank you.


when I measured the core size and did the maths it did come out at 1.26? So maybe it is 1.5 after all? 


thanks again

Yes -  the 0.48 mm diameter of each of the seven cores definitely sounds like "1.5 mm2" wire that I've seen. Have a go at measuring some other 1.5 mm2 or other sizes of cables you've bought recently, to compare. The actual size that each manufacturer uses could vary a bit,  depending on the quality of copper. 


All of the few cases I've actually measured have had that sort of difference, like 1.25 versus 1.5, between the actual and nominal cross-section. (I got started on measuring these when I noticed the insides of the flex supplied with an ebay-mediated imported floodlight. The outside of the flex was marked as 1.0 mm2, but the copper was almost invisible compared to the plastic - not far off headphone cable. Its actual area was below 0.5 mm2. I doubt very much that they were using specially [impossibly] good copper! The dangers of direct-imported electrical things are given some attention, but not enough.)