# Re: Wire gauge calc? (why the weird sequence)

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> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Wire gauge calc?
> Date: Thursday, January 07, 1999 11:44 AM
>
> Original Poster: David Huffman <huffman-at-fnal.gov>
>
>
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> Antonio,
> Were did this definition of the exact diameter come from? It must also
> include a temperature at which it is true. It is interesting that many
> charts have different values for a given gauge.
> Dave
More than 100 years ago, wire gauges were set pretty much by how much you
could reduce the diameter of the wire in one step through a wire drawing
die. For a variety of reasons, each reduction is about the same ratio,
leading to the geometric sequence we now have. There was, of course, a lot
of difference between various manufacturers and what they could get in one
pass, depending on the tension they were willing to use (higher tension =
more reduction in one pass, but higher probability of breaking), the alloy
being used, etc.

Around the turn of the century, they (I don't recall who, it is in my notes
from last summer, but I can't find them) decided to standardize, based on a
straight geometric progression, rounded off to 0.1 mil. They took the
current gauge 10 and gauge 40 at that time, and interpolated accordingly.
Oddly, the gauges don't have any relation to how many feet you get from
some volume or weight of material, like sheet metal gauges, or how many
spheres you can make for a given amount of material, like shotguns. And, of
course, every country decided to make its own table and gauges, hence the
difference between AWG (American wire gauge) and BWS (British Wire
Standard), B&S is Browne and Sharpe, and others...

Why differences between tables? 1) Differing precisions of calculations; 2)
transcription errors (most were done in the days before computers, and
typos do, in fact creep in, proofreading long tables of numbers is tedious
and error prone); 3) iconclastic manufacturers

Another thing to consider is that the most important characteristic for
most users of wire is the resistance per unit length (or more importantly,
the current carrying capacity, but that is set by max voltage drop at rated
load: resistance). If you are wiring a house or factory, or winding a
transformer, etc, the precise dimensions of the wire are unimportant, but
the series resistance is.

You might also find that wire, particularly surplus wire that has been
respooled, may not be round. Copper is quite soft, and it is easy to squash
it to an elliptical cross section.

>

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