Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics.

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ah, forgot to add the second part..

Posted by jneutron (A) on January 23, 2007 at 13:29:54

In Reply to: that is for a wire pair..not a single conductor, and it's kinda high. posted by jneutron on January 23, 2007 at 13:10:36:

cj: ""
"The self-inductance of a ROUND COPPER straight wire is on the order of 0.4 micro-henry/ft & is relatively UNaffected by the diameter or length of the wire".""

For a wire pair, the external inductance is dependent on the log of the ratio of distance to diameter...so to arrive at an inductance per foot, one needs the wire diameter..

For a #12 wire pair, a spacing of 1 inch gives very close to .4 uh per foot for the wire pair.

cj: ""
Also, your post gave me the impression that copper & silver share the same self-inductance. Please substantiate.""

The prev equation cited μ₀, as it was the derivation for a material which had a relative permeability of 1.

If you substituted steel for the conductor, with a relative permeability of 100, then the internal inductance would be larger by a factor of 100..in fact, this is what Hawksford did in that '85 paper, he substituted steel for the copper...Note, JC gave me the "100" number for the steel's permeability.

If you substitute silver for copper in a wire geometry, keeping the spacing and conductor diameter the same, you will be unable to measure a difference in inductance between the two constructs. This statement will fall apart as the frequency climbs towards a megahertz, as skinning will begin to reduce the silver's internal inductance slightly as a result of current re-distribution at the wire center. Given a wire pair inductance of 200 or so nH, the 30 total that can be removed by infinite frequency could only take the inductance down to 170 nH per foot.

Most cannot measure that accurately at the onset of the current redistribution regime..

Cheers, John

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