calculating max current through wire?

[Michael A. Terrell]

Yeah, a real smart system. Whats the next wire size larger than 0000 AWG?

The ))) type numbers were added long after the original system was
developed. How often do you wind a transformer with ))) wire, anyway?

I stand by my original comments, that circular mils are a stupid,
arbitrary and useless measure. WTF is wrong with conductor diameter?
Dude, R = Rho(T)*length/area, baby physics. Circular mils serve only to
complicate the matter unnecessarily.

Circular mils is very simple, if you think about it. You select the
rating you want: E.G.: 750 circular mils/amp * the current required and
take a look at the chart to select the wire, or a small range that will
work. Its worked for generations, whether you like it or not.

Even the "cookbook" approach becomes more complex, more stupid numbers
popping up everywhere, the almost complete lack of which is the main
advantage of the MKS system (hence the term "rational").

Use whatever you can wrap your mind around.

Another great example of stupid numbers is the penchant for using the
"transformer" equation. 4.44 is a pretty stupid number. E = wNBA is far
more meaningful.

I guess you would like to round pi off to 3.000? Personally, I just
write small programs to plug the numbers in and let it spit out the
answer. Do it once, and you're done. AWG wire is what is available to
me in the US. No matter how you feel about your metric wire gauges, its
irrelevant if I can't pick up a spool without ordering it from another
county.


--
Link to my "Computers for disabled Veterans" project website deleted
after threats were telephoned to my church.

Michael A. Terrell
Central Florida

 

[Terry Given]

Hi Michael,

The ))) type numbers were added long after the original system was
developed. How often do you wind a transformer with ))) wire, anyway?

if you deal with large currents, all the time

Circular mils is very simple, if you think about it. You select the
rating you want: E.G.: 750 circular mils/amp * the current required and
take a look at the chart to select the wire, or a small range that will
work. Its worked for generations, whether you like it or not.

It forces you to use a cookbook/ROT approach, starting with a current
density in circular mils per amp. What current density to use? That
depends entirely on the thermal environment of the wire. Odds on such a
design can be improved. Personally, I'd just do it right the first time.

Use whatever you can wrap your mind around.

very true.

I guess you would like to round pi off to 3.000? Personally, I just
write small programs to plug the numbers in and let it spit out the
answer. Do it once, and you're done.

whats rounded off in E = wNBA? NOTHING.

whats rounded off in E = 4.44fNBA? (note the hidden RMS)

4.44 <> 4.44288293817..... = pi*sqrt(2)


Personally, I do almost all of my maths by hand, with a pen and paper.
Admittedly I use an HP calculator for evil trig etc. I also use mathcad
and matlab (I keep trying to wean myself off mathcad, its slow and
buggy, but its so darned convenient),.

AWG wire is what is available to
me in the US.No matter how you feel about your metric wire gauges, its
irrelevant if I can't pick up a spool without ordering it from another
county.

Now thats a great reason to use AWG wire sizes. The abundance of US-made
gear means I have to be able to get it too (the lack of stuff made in US
nowadays means this problem will disappear in the next decade or so).

IMO Its still not a good reason to use circular mils, let alone in
conjunction with Rule-Of-Thumb current density figures. And yes, I
understand how to use circular mils. Just like I understand how to use
BTUs (Bloody Terrible Units), slugs etc. but of course never do.


Cheers
Terry