mm/swg/awg copper wire

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Tubetec

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Nov 18, 2015
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Im just going through a few finer grades of wire with a micrometer and digital vernier and comparing results with the tables here

https://www.rapidtables.com/calc/wire/awg-to-mm.html

Is there a difference in what were quoting between awg swg and mm , I have a roll of old UK made magnet wire , solderable , marked 36swg and 0.20mm  , measures right with the vernier ,when  I strip off the insulation  I measure 0.16mm diameter copper, when I try to use the calculator to get the resistance of 1 foot and compare the reading with the LCR Im a good bit out .
Does awg and swg refer to the diameter of the copper ,while the mm value is over all outside diameter including insulation ?
 
Tubetec said:
Does awg and swg refer to the diameter of the copper ,while the mm value is over all outside diameter including insulation ?
No, of course not. There are various coatings that also differ in thickness to comply with different temperatures, voltages, and environments. Diameter is always the copper.
 
wire gauge charts are good for getting you in the ballpark but matching up new wire to old wire can sometimes only be done by experimentation.

you might take apart a transformer and rewind it with wire of the same diameter only to find that the DCR is different.  maybe they used a single build insulation and you get wire with a heavy build. since your new wire has a smaller cross section of actual copper, the DCR will be higher.

or the other way around. they use a triple build, you match the diameter with a single build, now your DCR is lower.

since insulation has gotten better over the years, a single build today might measure smaller than the same gauge of a single build from 1950.  so if you measure wire from  1950 and order the same gauge according to diameter, then again, your DCR will be lower.

also, it is hard to tell single from heavy build on a piece of old wire, so if you do not have the original blueprint, you are pretty much guessing at the insulation used.

so,it can be trial and error. but it is not a bad thing to have a lot of different spools on hand for new projects. 

there are a million wire charts online and they all vary a little bit as to what gauge measures what. and the diameter can vary even as you de-spool the wire. that is why you will often see min, max and nominal specs.

you can notice this while you are winding, you wind two coils, and the second one has less room for the lams because the wire at that part of the spool was thicker.  that is of course if you keep the same tension and winding speed.

  if you are trying to wind a coil to match up  with a vintage coil, and the vintage coil is wound so that the window is completely filled, then variations can cause problems. if your wire starts running big, then you will run out of room. but as you wind more coils, you can get a feel as when this is about to happen and maybe use more tension to buy you some space.
 
Cheers CJ ,

I had been noticing some minor variations even in wire from the same batch ,  the 12.99 digital vernier out of lidl seems better than  my old micrometer  for checking the gauge. Thin wires above 40 are hard to strip the insulation from to get a meaningfull reading , flame tends burn the insulation and the copper oxidises as well .
 
I delved a little into the history of magnet wire . Turns out the Connolly Bros of Manchester were the first to perfect  insulated magnet wire in 1905 .

This particular roll  must be quite old as Connolly Bros were taken over in 1928 by BICC,  that would later become known as Essex  wire . 

Its marked 36SWG .0076  , all my measurements point to it being in fact 36 AWG

outside diameter including insulation is 0.2 mm(0.008in) , bare wire is 0.16mm (.0065in),
even the spool  is made from what looks like  wood fibres hot moulded with phenol formaldehyde resin,
it still has its charachteristic odour despite not being far off 100 years old .


 
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