Only you would ask that question Sparky. Good on ya mate! Let me show my age, it used to be varnish, coils were finished in varnished cambric, the cambric being a linen cloth. I still mix my own when I wantsta builds one but when I tear up the sheets BOY does the missus get mad
They are made a LOT more resistant to heat by I'm sure some fancy polymer. Maybe some manufacturer is peering in, but may be unwilling to give up the company secret.
I guess my answer is: It used to be varnish, varnish works fine, a little hard to work with but they do use better stuff now.
BTW, Table 8 shows DC resistance, nice place to start but doesn't have a big basis in reality for AC calcs. You weren't wrong in your answer, but you were .05 ohms off.....shame on you.
[This message has been edited by George Corron (edited 05-01-2002).]
I guess I'm not smart, but if the conductor is coated with varnish or some other "polymer", then why is the resistance different? My Code instructor taught us that the coating was tin/nickel, therefore a change in resistance.
tin/nickel is a coating, but a conductive one, you cannot have a conductive path, but an electromagnetic path. the varnish acts as an insulator so that the entire ball of copper may be used. Look at all the provisos under table 8. It is really a VERY general table, and due to change from manufacturer to manufacturer. Remember the first article of the code (OK up until 2002) "This code is not to be used as a design or specification guide" that's why.
I'll try this from a bit earlier point of view. In NEC Ch.9 table 8, coated vs. uncoated refers to tin plating over copper. The difference in resistance comes from both types having the same OD, but tin is less conductive than copper. So why the tin in the first place? Used to be that rubber (like in RHH/RHW) had some sulfur compounds that would corrode bare copper. Tin would limit that problem. With modern polymers the sulfur is no longer of concern, but some wire like SIS is still tin plated.
[Table 430-149 for 2-phase motors still...1999 anyways.]