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<div class="moz-cite-prefix"><br>
Isn't Wikipedia wonderful ! That's one internet outfit that I
donate too...<br>
<br>
So, what I was confused about in Larry's posting of the wire table
was that they showed<br>
AWG/KCMIL and all that meant was that some values were in AWG and
some values<br>
were in KCMILs. <br>
<br>
Wire gauge to diameter and cross sectional area and the reverse<br>
operation are very handy little programs I have kept in my HP
calculator<br>
for many years... Uses some of those formulas of course shown in
your<br>
Wikipedia paste.<br>
<br>
I had heard there was a special "electricians" calculator years
ago...<br>
Does that have all these conversion in it too ?<br>
<br>
boB<br>
<br>
<br>
On 12/2/2014 5:45 PM, Jerry Shafer wrote:<br>
</div>
<blockquote
cite="mid:CAMUFgmU-4WRacFtL=asyvYzaYT8wr519hpGM9QGHT59v0RmuPw@mail.gmail.com"
type="cite">
<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
moz-do-not-send="true" 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 moz-do-not-send="true" 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 moz-do-not-send="true" 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 moz-do-not-send="true" 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 moz-do-not-send="true"
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 moz-do-not-send="true" 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
moz-do-not-send="true" href="mailto:boB@midnitesolar.com">boB@midnitesolar.com</a>
<span dir="ltr"><<a moz-do-not-send="true"
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 moz-do-not-send="true"
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:part10.01010301.06000000@midnitesolar.com"
alt=""><br>
On 12/2/14 3:54 PM, <a moz-do-not-send="true"
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>
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