<div dir="ltr">To All Here is the math from wikipedia<br><p>By definition, No. 36 AWG is 0.005 inches in diameter, and No. 0000
is 0.46 inches in diameter. The ratio of these diameters is <b>1:92</b>, and
there are 40 gauge sizes from No. 36 to No. 0000, or 39 steps. Because
each successive gauge number increases diameter by a constant multiple,
diameters vary geometrically. Any two successive gauges (e.g. A & B )
have diameters in the ratio (dia. B ÷ dia. A) of <img class="" alt="\sqrt [39]{92}" src="http://upload.wikimedia.org/math/f/d/0/fd0576bc7a7c22e7f482efa1de034f92.png">
(approximately 1.12293), while for gauges two steps apart (e.g. A, B
& C), the ratio of the C to A is about 1.12293² = 1.26098. The
diameter of a No. <i>n</i> AWG wire is determined, for gauges smaller than 00 (36 to 0), according to the following formula:</p>
<dl><dd><img class="" alt="d_n = 0.005~\mathrm{inch} \times 92 ^ \frac{36-n}{39} = 0.127~\mathrm{mm} \times 92 ^ \frac{36-n}{39}" src="http://upload.wikimedia.org/math/f/6/d/f6d1ec86b3acdec9d5af9282a34a7f0c.png"></dd></dl>
<p><small>(see below for gauges larger than No. 0 (i.e. No. 00, No. 000, No. 0000 ).)</small> or equivalently</p>
<dl><dd><img class="" alt="d_n = e^ {-1.12436 - 0.11594n}\ \mathrm{inch} = e^ {2.1104 - 0.11594n}\ \mathrm{mm} " src="http://upload.wikimedia.org/math/b/f/a/bfa87cffe117d988403267ea4e1537d8.png"></dd></dl>
<p>The gauge can be calculated from the diameter using</p>
<dl><dd><img class="" alt="n = -39\log_{92} \left( \frac{d_{n}}{0.005~\mathrm{inch}} \right)+36 = -39\log_{92} \left( \frac{d_{n}}{0.127~\mathrm{mm}} \right)+36" src="http://upload.wikimedia.org/math/a/4/a/a4a6e74e48825a2d5de74baf1aa4ada8.png"> <sup id="cite_ref-3" class=""><a href="http://en.wikipedia.org/wiki/American_wire_gauge#cite_note-3"><span>[</span>3<span>]</span></a></sup></dd></dl>
<p>and the cross-section area is</p>
<dl><dd><img class="" alt="A_n = \frac{\pi}{4} d_n^2 = 0.000019635~\mathrm{inch}^2 \times 92 ^ \frac{36-n}{19.5} = 0.012668~\mathrm{mm}^2 \times 92 ^ \frac{36-n}{19.5}" src="http://upload.wikimedia.org/math/0/1/f/01f2a8866588007b257186f3fb14878d.png">,</dd><dt>Do you want more</dt><dd>Jerry<br></dd></dl><br></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Dec 2, 2014 at 2:20 PM, <a href="mailto:boB@midnitesolar.com">boB@midnitesolar.com</a> <span dir="ltr"><<a href="mailto:boB@midnitesolar.com" target="_blank">boB@midnitesolar.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<div><br>
The only thing I can think that AWG/KCMIL means is that it is a
ratio ?<span class="HOEnZb"><font color="#888888"><br>
<br>
boB</font></span><div><div class="h5"><br>
<br>
<br>
On 12/2/2014 4:18 PM, <a href="mailto:boB@midnitesolar.com" target="_blank">boB@midnitesolar.com</a> wrote:<br>
</div></div></div><div><div class="h5">
<blockquote type="cite">
<div><br>
I'm pretty sure that Daniel Young's explanation of surface area
explains the discrepancy.<br>
<br>
The surface area of a larger wire does not grow as fast as its
cross sectional area so<br>
it does not cool as well. It can carry more current but its
surface and temperature<br>
rise is going to be higher if you simply put more amps through
it proportional<br>
to the wire area. <br>
<br>
But the wire table does not show multiple wires in parallel
and/or the distance<br>
between them. Or is there such a table ? If the distance
between them are high<br>
enough so that the heat can be dissipated, then you ~should~ be
able to get<br>
3 times the ampacity of all 3 wires in parallel ? Shouldn't he
?<br>
<br>
What exactly does the title of that column mean ? AWG/KCMIL ?<br>
AWG and KCMIL are different. AWG goes higher as the wire gets
smaller.<br>
KCMIL (area) gets higher as the wire gets bigger.<br>
<br>
boB<br>
<br>
<br>
<br>
<br>
On 12/2/2014 3:32 PM, Larry wrote:<br>
</div>
<blockquote type="cite">
<div>Hey boB,<br>
<br>
This is the reference table I was using. They show 325 AWG and
325kCM refer to the same diameter cable but I should have used
kcm for clarity. <br>
<br>
If all insulation/temp rating is the same we are back to my
original question. Anyone else able to explain this? To be
safe I am leaning toward using the combined CM number to size
for current rather than 3 times the ampacity as that just
makes no sense to me. <br>
<br>
<img src="cid:part1.09020901.01090104@midnitesolar.com" alt=""><br>
On 12/2/14 3:54 PM, <a href="mailto:boB@midnitesolar.com" target="_blank">boB@midnitesolar.com</a>
wrote:<br>
</div>
<blockquote type="cite">
<div><br>
The "area" of the conductor will be 3 times and you would
think that the NEC Ampacity would also be 3 times<br>
that of one conductor. But one LARGE conductor with the
same area might not be as high as you think<br>
because of insulation. I would think that ampacity of 3
cables in parallel would be 3 times. But probably<br>
not when you take a single cable of the 3X area out of the
NEC table. (I haven't looked at this to verify)<br>
<br>
Also, Larry, 325 AWG 750 AWG (gauge) wire is a bit too
small for this, don't you think ?<br>
<br>
I know... You mean circular mils...<br>
boB<br>
<br>
<br>
</div>
<blockquote type="cite">
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