I've often wondered why why CSA is used rather than diameter, perhaps it goes back 100 years to when wire was sometimes drawn into square section strands. Then there's AWG and SWG to contend with. Perhaps what is needed is digital callipers with a button to do the pi r ^2 thing...
elecrical cable guage / dia / area FAQ
Nov 20, 2024
Last reply: 1 year ago
10 Replies
When people refer to 1.5 mm cable I take it that's the area of the cross section, sometimes seen as 1.5 mm2 ??
So if the copper appears to be slightly wider in dia than 1mm it's probably 1mm wire? and 1.5mm wire actually is about 1.5mm dia. Is that how it works?
How do you tell them apart? Is it just experience? By feel.
TW
On T&E it also stamped into the outer sheath every so often.
CSA is useful in calculations for resistance. From diameter you have to go via pi*(d/2)^2 which is a bit more annoying. Also the area numbers are easy to use - 1, 1.5, 2.5, 4, 6, 10, 16, 25 which you don't get from diameter. eg you know that a 25mm2 has 10/25 = 40% of the resistance per metre than a
10mm2. The same goes for weight, which is linear with CSA.That seems to be because there's no round number in actual units so they just invent a round number and say it's a 'standard'.
It gets rather embarassing that they have to define 0000 AWG when they run out of numbers.
Possibly, although I'm not sure many people are actually measuring things. Also they aren't accurate enough for smaller wire sizes.
Theo
Why not? I've got a tape measure where the reverse side of the blade is marked in pi.cm, for measuring diameters.
Surely the diameter is different for the same CSA, between solid and stranded cores, due to the airspace between strands?
Yes, for stranded you switch to diameters, e.g. 7/0.1 for lightweight signal wires, 3/026 and 7/026 for old domestic imperial wiring sizes.
Yup
Yup. See the table here:
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By feel[1], and you can also look at the outer sheath of the cable - sizes in the table are approximate but usually near enough. Also the outer jacket may have the CSA printed or embossed on it.
[1] and also how much of a bastard it is to get neatly dressed and into terminals!
But less useful if you're stuffing higher frequencies down that cable/wire. Then it's the circumference that matters.
If it's a high frequency cable it's usually some kind of twisted pair or coax, which are sold by insertion loss over a frequency range not by cable area. Domestic mains wiring tends not to worry about that. OK, Homeplugs try stuffing high frequencies down it, but the results are unsurprisingly awful.
Theo
Just don't mention Litz wire.
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