Re: AWG WIRE TABLE for Coilers (fwd)

---------- Forwarded message ----------
Date: Sun, 3 May 1998 17:56:01 -0700 (PDT)
From: "Edward V. Phillips" <ed-at-alumni.caltech.edu>
To: tesla-at-pupman-dot-com
Subject: Re: AWG WIRE TABLE for Coilers (fwd)

	Apparently the American Wire Gauge was defined by the
AIEE as early as 1893.  See the following:


	Charles N. Underhill

page 215:  (The rather quaint language is exact quote.)
"109. American Wire Gauge (B.& S.)

     This is the standard wire gauge in use in the United

States.  It is based on the geometrical series in which

No. 0000 is 0.46 inch diameter, and No. 36 is 0.005 inch diameter.

	Let n = number representing the size of wire.

	    d = diameter of the wire in inch.

	Then log d = 1.5116973 - 0.0503535 n,                     (187)

         - 0.4883027 - log d
     n = -------------------                               (188)

    n may represent half, quarter, or decimal sizes.

	If d represent the diameter of the wire in millimeters,

then    log d = 0.9165312 - 0.0503535 n,                   (189)

         0.9165312 - log d
and 	n = -----------------                                 (190)

	The ratio of diameters is 2.0050 for every six sizes,

while the cross-sections, and consequently the conduc-

tances, vary in the ratio of nearly 2 for every three sizes."

	In a reference on the following page these expressions are

attributed to the "Supplement to Transactions of the American

Institute of Electrical Engineers", October, 1893. 

     As for wire resistance, the resistivity at a constant

temperature can vary by several percent, depending on the purity

of the copper and its mechanical treatment, so the values 

for resistance given in the wire tables are approximations.

The resistivity of "pure annealed copper" is given as

1.584 x 10^-6 ohm-cm, while that of "hard-drawn copper" is given

as 1.619 x 10^-6 ohm-cm.

     I have no idea of the tolerance on manufactured wire

diameter, but can't imagine it being much better than a percent

for large sizes and worse than that for very small sizes, so the

above formulae have more precision than circumstances warrant.

I, personally, find the standard wire tables quite adequate.

     By the way, this book is now available from Lindsay

Publications, and I recommend it to anyone interested in the

design of solenoids or other electromagnets.

     The equations above are exact quotes from the original

and may get screwed up in transmission.

These should not:

     n = (-0.4883027 - log d)/0.0503535  (d in inches)  (188)

     n = (0.9165312 - log d)/ 0.0503535  (d in mm)      (190)


	Of course, nothing says the AIEE didn't have sheet metal
gauges in mind when they wrote the referenced material.