Explain wire sizing to me please.

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fredrussell

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I've always been baffled by wire sizing and a recent thread on solar panel wire gauge has made me think I need to check my wires to regulator is correct size - my hunch is that its too thin.

So I'm using the following table on AWG from Wikipedia (scroll down page a bit:

https://en.wikipedia.org/wiki/American_wire_gauge

...and generally it all makes sense to me. Whats confusing me is this; I have a reel of Durite "Auto Cable". The label reads as follows:

Part: 0-943-08
Single Cable
Yellow PVC
28/0.30mm
50 Metres

Am I right to assume that a) what is measured is the conductor part of cable, and b) in the fourth line of that label, "28" refers to its AWG, and 0.30 refers to its diameter in mm?

Measured with my vernier gauge, the diameter of the conductor is approx 1.8mm, so where is this 0.30mm figure coming from?
 
fredrussell said:
I've always been baffled by wire sizing and a recent thread on solar panel wire gauge has made me think I need to check my wires to regulator is correct size - my hunch is that its too thin.

So I'm using the following table on AWG from Wikipedia (scroll down page a bit:

https://en.wikipedia.org/wiki/American_wire_gauge

...and generally it all makes sense to me. Whats confusing me is this; I have a reel of Durite "Auto Cable". The label reads as follows:

Part: 0-943-08
Single Cable
Yellow PVC
28/0.30mm
50 Metres

Am I right to assume that a) what is measured is the conductor part of cable, and b) in the fourth line of that label, "28" refers to its AWG, and 0.30 refers to its diameter in mm?

Measured with my vernier gauge, the diameter of the conductor is approx 1.8mm, so where is this 0.30mm figure coming from?
Click to expand...

The cable you describe is 2.0mm² "28/0.30mm" means 28 strands, .3mm each.

Better to work in mm² rather than AWG, which is an American measurement.
 
AWG - American wire gauge is simply how many turns of wire around a cylinder would lay next to each other in a 1" length of the cylinder. So the higher the number the smaller the cable size. ISO standards uses the total cross sectional area of the individual strands forming the conductor as measured in mm sq.
 
superheat6k said:
AWG - American wire gauge is simply how many turns of wire around a cylinder would lay next to each other in a 1" length of the cylinder.
Click to expand...

Thanks, that's interesting. I always assumed it was just a completely arbitrary number.

I'd suggest avoiding it in favour of square millimeters unless you're forced to use it for some reason (eg US-made equipment talking about how it should be installed). For one thing, the wire you buy on this side of the Atlantic will be in mm2 in pretty much every case.

Pete
 
prv said:
Thanks, that's interesting. I always assumed it was just a completely arbitrary number.

I'd suggest avoiding it in favour of square millimeters unless you're forced to use it for some reason (eg US-made equipment talking about how it should be installed). For one thing, the wire you buy on this side of the Atlantic will be in mm2 in pretty much every case.

Pete
Click to expand...
Surprising I suppose that they don't refer to it as British Wire Gauge after all they still refer to their preferred imperial system of measurements still as 'British' or 'English', whilst we metricated decades ago.
 
PaulRainbow said:
The cable you describe is 2.0mm² "28/0.30mm" means 28 strands, .3mm each.

Better to work in mm² rather than AWG, which is an American measurement.
Click to expand...

Just in case your high school maths is rusty - to get from diameter to cross sectional area

A = PI x r²

r = diameter / 2 = 0.3mm /2 = 0.15mm

A = 3.14 x (0.15 x 0.15) = 3.14 x ( 0.0225) = 0.071

28 x A = total = 1.98mm² So pretty much 2mm²

From your measured diameter: 1.8mm -- A = 3.14 x ( (1.8 /2 ) x (1.8/2)) = 3.14 x (0.9 x 0.9) = 3.14 x 0.81 = 2.54mm² - because your measured diameter includes gaps between the 28 strands. So if you are measuring multistrand wire diameter and calculating expect to over estimate

Sorry that may be completely unnecessary explanation but some people wont have done circle area maths for 40 years and so might have needed a quick recap.
 
superheat6k said:
AWG - American wire gauge is simply how many turns of wire around a cylinder would lay next to each other in a 1" length of the cylinder. So the higher the number the smaller the cable size. ISO standards uses the total cross sectional area of the individual strands forming the conductor as measured in mm sq.
Click to expand...

Thats not right. See https://en.wikipedia.org/wiki/American_wire_gauge
 
ShinyShoe said:
Just in case your high school maths is rusty - to get from diameter to cross sectional area

A = PI x r²

r = diameter / 2 = 0.3mm /2 = 0.15mm

A = 3.14 x (0.15 x 0.15) = 3.14 x ( 0.0225) = 0.071

28 x A = total = 1.98mm² So pretty much 2mm²

From your measured diameter: 1.8mm -- A = 3.14 x ( (1.8 /2 ) x (1.8/2)) = 3.14 x (0.9 x 0.9) = 3.14 x 0.81 = 2.54mm² - because your measured diameter includes gaps between the 28 strands. So if you are measuring multistrand wire diameter and calculating expect to over estimate

Sorry that may be completely unnecessary explanation but some people wont have done circle area maths for 40 years and so might have needed a quick recap.
Click to expand...

For the area of a circle my grandad just multiplied the diameter squared by .7857
seems that he reckoned the less figures involved the less chance of a mistake
But what did he know ? He left school at 11 yrs

1.8 * 1.8 * .7584 = 2.546

More than me because I typed 7857 first time- now edited !!!!!
 
Last edited:
Daydream believer said:
My grandad just multiplied the diameter squared by .7857
seems that he reckoned the less figures involved the less chance of a mistake
But what did he know ?
1.8 * 1.8 * .7587 = 2.546
Click to expand...

Thats OK, except he should have used 0.7854 which is simply pi/4
 
Daydream believer said:
Actually I thought it was .7854 but when i stuck it in a quattro spreadsheet it seemed to get the wrong answer so i did it again by division & came with the 7
that is why I edited my post. Thanks for correcting me
Click to expand...

" Spreadsheet" ? I use my trusted Texas Instruments Ti35 pocket calculator for all my arithmetic ...... probably nearly 30 years old and still going strong. :)
 
we never did actually go metric in a lot of engineering applications here, we merely added a metric equivilent to an earlier imperial fraction. Hence in my world we work with tubes with decimals of mm, for instance 33.7, 44.5, and sheet material in the same way, funny amounts of mm that are the old fraction or with AWG.
To bend a 33.7mm dia we use the correct tool from the US, which is only available in it imperial fraction measurement!

Our tube bending CAD software has an additional interface to cope with all that. The sheet metal bending software works in AWG, and gets buggy when you try to convert. It is simpler to stay yank with our stuff, and just order the materials in mm!
It is interesting that little has really changed in the last couple of hundred years but the way metal measurements are expressed. Hence the odd numbers with electrical wire too
 
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