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<p>Yes, T2 is the conductor temp. I use 25C for wire in underground
conduit that around here is close to earth temp, 15C. Just
depends on how much current is flowing, but the idea of doing volt
drop calcs with the wires running at max temp seems over kill in
many cases. 75C means that you are 1C away from exceeding the
temp rating of many of the connector lugs. </p>
<p>Ray Walters<br>
Remote Solar</p>
<div class="moz-cite-prefix">On 3/22/2026 8:06 PM, Corey Shalanski
via RE-wrenches wrote:<br>
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<div>Hi Ray,</div>
<div><br>
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<div>RE. the <i>NEC</i> Chapter 9 Table 8 resistance adjustment
formula: I believe temperature T2 is the operating temperature
of the conductor - not necessarily ambient temperature...
unless I'm mistaken?</div>
<div><br>
</div>
<div>Corey Shalanski</div>
<div>Jah Light Solar</div>
<div>Portland, Jamaica</div>
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<div dir="ltr" class="gmail_attr">On Sat, Mar 21, 2026 at
7:20 PM Ray Walters <<a href="mailto:ray@solarray.com"
moz-do-not-send="true" class="moz-txt-link-freetext">ray@solarray.com</a>> wrote:<br>
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style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">
<div class="msg-7238687081896949649"><span
style="font-family:"Times New Roman",serif;font-size:12pt">I
remember doing some measurements on a long wire run, and
being surprised that the actual voltage drop was much
less than the calculations. That's when I found a small
note at the bottom of the NEC Table 8 conductor
properties used for official VD calculations. The
resistance is listed at 167 F (75C), so if you use the
adjustment equation in Note 2, it is much less VD, and
corresponds to reality. For underground conductors, I
might use 25C. Use common sense. </span><br>
<div>
<p>The formula is R2=R1 (1+ a(T2-75))</p>
<p>I made a spread sheet about 15 years ago, that uses
that formula for doing wire sizing. Happy to share,
if anyone is interested.</p>
<p>Ray Walters<br>
Remote Solar</p>
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