Electrical conductivity in steel wire ?

In our local paper someone stole a 3500 foot spool of No. 4 copper wire that was worth $8500. No wonder people want to use steel fence wire. On the KLI/CMA this is the method used by the Neher McGrath paper to find DC resistance. Multipliers are used to convert to AC resistance or impedance. The paper was written in 1957 using feet and not meters. K for steel at 20 degrees C is 95.8 ohms per foot. To find the resistance at other temperatures the inferred temperature at zero resistance is required and the point slope equation is used to find the equation of the straight line. This is not entirely correct because the actual measured values of resistance are slightly off the straight line, but for most field applications it is good enough. Th N-M paper in PDF format is at:

I have no problem with the calculator per se. You have clarified the terms satisfactorily. It is based on knowledge that dates back to at least the time of Ohm (well before 1900). The 1957 reference apparently uses an older cookbook expression as part of dealing with ampacities of underground cables.-Unfortunately, I could not bring up the reference from your site but it is an AIEE paper dealing with ampacities of underground cables- a much more complex problem than simply finding resistance and voltage drops which can be found in any decent introductory circuits text. The resistance/ temperature relationship has also been around for a long time. Actual measured data do have errors which cause wobbles in the curve so least squares fitting is used.

The AC corrections do depend on frequency and wire size and the typical corrections for copper wire will be incorrect for iron wire (and for closely wound coils) because of enhanced magnetic effects leading to what is called "skin effect" (Rudenberg tackled this messy problem about 80 years ago (+/-)) .

Skin depth has the same functional, dependence upon permeability as it does for frequency or conductivity.

Bill

| In our local paper someone stole a 3500 foot spool of No. 4 copper | wire that was worth $8500. No wonder people want to use steel fence | wire.

Do we see a pattern here?