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why is the US not Metric
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Dek:
I use ft and inches for doing rough arse stuff i.e. "about 1 3/4" is near enough.
I use metric when undertaking something needing a jot more precision "that's exactly 44.450mm"
 :box:
 ;)
Dek
Zero999:

--- Quote from: KL27x on January 21, 2020, 12:08:41 pm ---
--- Quote from: Zero999 on January 21, 2020, 10:34:44 am ---That sounds very complicated and only reaffirms my point: it's much easier to use physical dimensions such as cross-sectional area or even diameter. Take a step back. Suppose you've never heard of AWG or SWG. If you saw a drawing with cable cross-sectional area specified, then it would be obvious what it means. No need to look anything up. We're not even talking about metric vs imperial here, but simply defining a physical property vs some complex system. Even wire diameter in inches or thou would be much easier to use.
--- End quote ---
Easier to use...for who, though?
Have you ever had to spec an SIL/DIL PCB connector that comes in multiple numbers of connections? And then you have to use some formula of (n+1)*dimensions/pins/pads on the footprint mechanical drawing to even create the PCB footprint? Wouldn't it be "so much easier" if they just listed the footprint for every single size of connector? (Heck, wouldn't it be easier if they even showed the entire footprint for just one of these components, say the smallest one, just for reference?>:D) But they don't usually do this. And there are communication/clarity/future-proofing reasons for this decision, as well as efficiency/brevity.
--- End quote ---
Fairly simple, because they already give you the pitch, so there's no point in a drawing. I don't have to faff around looking things up. A bit of arithmetic isn't hard and CAD software does most of it for me.


--- Quote ---If I had never heard of or seen AWG? I would look it up and RTFM. How would that be any worse than just guessing what diameter of wire I need? Or do you suppose you just learn the conductance of copper per square mm per meter in high school and remember it ever after? And then have to do algebra to figure out the minimum diameter you need, including heat dissipation and ambient temp and temp coefficient, and then still have to look up the closest size? (And still not know the actual legal/lawyer ampacity?)
--- End quote ---
More often than not, it's unnecessary to worry about the ampacity, because the current is way below the limiting factors of volt drop and insulation temperature rating.


--- Quote ---You seem to be concerned with "ease of use" for Jack and Jane, specifically. In America, perhaps we are more concerned that our brighter bulbs have as much info as could possibly be useful to them in making an informed decision and not so very much concerned if Mary Sue Arduino-noob easily can begin to calculate for herself the cheapest possible wire to theoretically do some job and hopefully do it right. We will forgo this 0.0013% of the wire market to better serve the vast majority.
--- End quote ---
How is a weird gauging system somehow more straightforward than simply specifying a physical dimension?

There are other wire gauging systems than AWG. Suppose a drawing specifies 19SWG, I'd have to Google it, but if it simply said a diameter of 40 thou (I had to look that up), I'd immediately know it's just over 1mm. Not having to refer to charts or Google everything makes designing things such as PCBs much easier.


--- Quote ---
--- Quote ---Here in the UK we use a stupid system for shoe sizes. I wish we'd move over to something more straightforward, based on simple dimensions.

--- End quote ---
You mean more sizes/shapes/combos? Or just a more intuitive way to name them?  The former, yeah. The latter? Well, most people only have to figure that out so many times until their feet stop growing.  >:D

--- End quote ---
In the old days it was less of an issue, since one would go into a shoe shop and get their feet measured, but nowadays people more often than not order online, so will have to measure at home. Yes you're right, it's less of an issue for adults, but getting the right size shoes for children is always fun.
KL27x:

--- Quote ---How is a weird gauging system somehow more straightforward than simply specifying a physical dimension?
--- End quote ---
I didn't say it was more straightforward. I implied/contended that it has the benefits of ease and clarity of communication, that it conveys more and potentially useful information/data to potential customers, and that it may provide future-proofing.

1. Ease of communication: When I run low of "bodge wire," I buy more "30 AWG Kynar." I don't have to remember "0.0231 mm^2" (made up number). If I search for "0.0220 mm^2 wire," and nothing comes up, then I just go up by a thous and try again, 60-70 times?  If I search for a specific type of "0.0231 mm^2 wire," and I get no hits, is it because no one makes the wire in this size, or did I enter that physical dimension/name incorrectly? Does India make 0.0231, or is 0.0233 their standard? The people who enter the wire market can list under the most appropriate gauge, then give the actual physical dimensions of this specific product in the description. Same seller might sell several products of the same gauge wire but with slightly different actual dimensions. Even among American manufacturers, you can expect some variations due to different die manufacturers and die and tool wear and human inputs, let alone manufacturers in different countries.   

2. Conveys more data: I know all the sizes that are available. I know the size of the steps between between each size.

3. Future-proofing: The AWG standard is not dependent on a measuring system. It is equally accessible to either metric or USC. And it will be equally accessible to metric 2.0, whatever that is and whenever that day comes. :)
Zero999:

--- Quote from: KL27x on January 22, 2020, 11:06:03 am ---
--- Quote ---How is a weird gauging system somehow more straightforward than simply specifying a physical dimension?
--- End quote ---
I didn't say it was more straightforward. I implied/contended that it has the benefits of ease and clarity of communication, that it conveys more and potentially useful information/data to potential customers, and that it may provide future-proofing.

1. Ease of communication: When I run low of "bodge wire," I buy more "30 AWG Kynar." I don't have to remember "0.0231 mm^2" (made up number). If I search for "0.0220 mm^2 wire," and nothing comes up, then I just go up by a thous and try again, 60-70 times?  If I search for a specific type of "0.0231 mm^2 wire," and I get no hits, is it because no one makes the wire in this size, or did I enter that physical dimension/name incorrectly? Does India make 0.0231, or is 0.0233 their standard? The people who enter the wire market can list under the most appropriate gauge, then give the actual physical dimensions of this specific product in the description. Same seller might sell several products of the same gauge wire but with slightly different actual dimensions. Even among American manufacturers, you can expect some variations due to different die manufacturers and die and tool wear and human inputs, let alone manufacturers in different countries.   

2. Conveys more data: I know all the sizes that are available. I know the size of the steps between between each size.

3. Future-proofing: The AWG standard is not dependent on a measuring system. It is equally accessible to either metric or USC. And it will be equally accessible to metric 2.0, whatever that is and whenever that day comes. :)

--- End quote ---
There are standard cross-sectional areas for commonly used wire sizes. You don't often get 0.52mm2, but convenient sizes such as 0.5mm2, 0.75mm2, 1mm2, etc. unless it's AWG or SWG, converted to meaningful SI units.

AWG does not convey more data than simply stating the cross-sectional are. It means nothing, without looking up the dimensions, unless you're so familiar with it you can remember them. AWG just makes things more difficult. Writing a computer program to work out the resistance of a piece of wire specified by cross-sectional area is easy. Doing the same for SWG or AWG is a PITA. It would require a look-up table or a monster switch case statement.

AWG is not future proof, compared to SI units, which will never go away. Some European suppliers are moving away from AWG, in favour of cross-sectional area. Most suppliers use both in their search engines, but the section of the RS Components catalogue linked below, only lists cross-sectional area.
https://uk.rs-online.com/web/c/cables-wires/wire-single-core-cable/automotive-wire/
KL27x:

--- Quote ---There are standard cross-sectional areas for commonly used wire sizes. You don't often get 0.52mm2, but convenient sizes such as 0.5mm2, 0.75mm2, 1mm2, etc. unless it's AWG or SWG, converted to meaningful SI units.
--- End quote ---
What makes you think these are the only sizes you will encounter outside of the US? Is there one die maker to supply all the wire manufacturers? Or is this the catalog of standard sizes that every country and every manufacturer within each country outside of the US have decided upon and adhere to within a proscribed tolerance limit, resulting in a standard chart which you have conveniently memorized?

These dimensions are nicely truncated on purpose. Cuz someone made those decisions and everyone agrees. (Like how some countries have 700mL bottle for hard liquor, while others use 750mL; that is sarcasm). If the actual dimensions of the wire match these artificially truncated standards, then you necessarily made your wire manufacturing less efficient by deviating from the 10.5% diameter reduction per die.

E.g., from your link, the list of sizes by cross section is significantly longer than the AWG list. Even though there are essentially an equal number of products (1826 vs 1824; out of 2000 total, so over 90% of wires are happily listed under both categories) between the ones sortable by AWG and those by metric. You will notice lots of sizes that are very close, in the dropdown menu, like 0.22, 0.23, 0.24, 0.25, 0.26 mm^2. Those are less than 5% increases in area each step up. Vs 26% between each AWG size through that same range (through the entire range). This occurs again in several spots on the cross section drop down menu.

And... considering the traffic jam, here, would you confidently design a spec for "0.26mm^2" wire, wondering if that will be an available size in 40 years? Maybe the metric market will consolidate on 0.25mm^2 as a standard to absorb some of those other sizes? America AWG system kinda planned this all out to cover the entire range, efficiently, and in a way that you don't have those questions.


--- Quote ---Writing a computer program to work out the resistance of a piece of wire specified by cross-sectional area is easy. Doing the same for SWG or AWG is a PITA. It would require a look-up table or a monster switch case statement.
--- End quote ---
Then don't do that. Firstly, you could input the actual dimensions for the wire, whether you buy it by cross sectional area or AWG. The actual dimensions and tolerances will determined by the actual product/datasheet, not by the name/standard it falls under for classification. If you make software that goes by gauge, I think the metric version of the software should also have a look-up table, too, so there's  dropdown list of the available metric sizes that are apparently standardized worldwide by every other nation? That increases the utility, no?

The software side is the least of your worries. We're talking a wire manufacturing and distribution and marketing machine. The software is just a tiny afterthought. The ease of use is not a major factor. It's the very few customers who make large repeat order who you want the crystal clear communication and standardization in order to serve. The rest just have to deal with it.
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