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that is for a wire pair..not a single conductor, and it's kinda high.

As such, it depends heavily on the actual wire spacing. The best one can hope for is zero thickness insulation and about 160 nH, or .16 uH per foot, for a wire pair. Nobody uses zero thickness insulation of course.

The terman equation is best for calculation of a wire pair inductance, but that also has a component of the equations which has the 15 nH per foot internal (or self) inductance number I quoted..
Here is the self (or internal) inductance for a cylindrical wire:

Albert Shadowitz, "the electromagnetic field", Dover, 1988, pages 216-217..

Note, I can't put the integral equations here, suffice it to say he completed the derivation, the formula I'll give is the end result..

The total inductance for a single cylindrical conductor is:

Lint = μ0 / 8 π.

μ0 = 4 π times 10-7 henries/meter.

This becomes (4 π /8 π)times 10-7 henries/meter

or, 1/2 times 10-7 henries/meter

this is 5 times 10-8 henries/meter

or, 50 times 10-9 henries/meter

50 nanohenries per meter.

12/39.4 = .304 feet/meter.

50 times .304 = 15.2 nanohenries per meter.

(Ok, so I rounded the .2 off)

Cheers, John



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