Confused with PI Xls' Cmils calculation
Hi,
I'm using PI Xls and I'm confused by the Circular Mil Area (Cmils) calculation on row 95. If I enter a wire diameter of 0.57mm, for 23 AWG, the conductor diameter is given as 0.50mm. This gives me a Cmils of 323.
From http://en.wikipedia.org/wiki/Circular_mil, I should be able to square the diameter in mils. 0.50mm = 19.685 mil, and 19.685^2 = 387.499. This calculation matches the table at http://www.interfacebus.com/Copper_Wire_AWG_SIze.html.
Obviously, 323 != 387.499. Can you please help explain to me how PI Xls calculates Cmils, and where I'm getting confused? Thank you.
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Thanks for the reply, Spock.
I'm working with TOP268, so the TOP-JX spreadsheet.
Your calculation matches the data in PI Xls, but it doesn't match the equation I posted above. I would have assumed all Cmils calculations would end up with the same number, but apparently not...
Can you comment on the equations I added above? Are they incorrect?
They are ultimately both approximations - so you have to take both numbers with a grain of salt.
I don't know if the Wikipedia one assumes bare copper diameter or not. Some wires are single coated and others are double coated for stronger insulation - you have to check what wire this is applicable to.
See http://www.powerint.com/sites/default/files/product-docs/an16.pdf
scroll to pages 20 -21 (thereabouts) for a slightly better discussion on this topic
Which (product) spreadsheet are you referring to?
In general the relationship between circular mils (CM) and AWG is given by
CM = 2^((50-AWG)/3)