# why circular mils



## HARRY304E (Sep 15, 2010)

123 said:


> Does anybody know why a circular mil area measurement was created,
> when square mil area would have been the logical choice of the times?


http://en.wikipedia.org/wiki/Circular_mil


*American wire gauge* (*AWG*), also known as the *Brown & Sharpe wire gauge*, is a standardized wire gauge system used since 1857 predominantly in the United States and Canada for the diameters of round, solid, nonferrous, electrically conducting wire.[1] The cross-sectional area of each gauge is an important factor for determining its current-carrying capacity.


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## cultch (Aug 2, 2011)

Cause the wire is circulur not squared?


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## bkmichael65 (Mar 25, 2013)

Much easier to square the diameter instead of dividing the diameter in half, squaring it and then multiplying by pi


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## Cletis (Aug 20, 2010)

bkmichael65 said:


> Much easier to square the diameter instead of dividing the diameter in half, squaring it and then multiplying by pi


How are the air pockets accounted for ?


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## HARRY304E (Sep 15, 2010)

Cletis said:


> How are the air pockets accounted for ?


If you have air pockets , then you need to make more money to fill them...:laughing:


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## 480sparky (Sep 20, 2007)

Cletis said:


> How are the air pockets accounted for ?


You just fly through them. :whistling2:


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## 123 (Oct 28, 2012)

bkmichael65 said:


> Much easier to square the diameter instead of dividing the diameter in half, squaring it and then multiplying by pi


In a pre-calculator world this makes sense.
But imagine during a high school math test calculating an area of a circle 1 inch in diameter,
instead of A = 3.14 x 0.5 square = 0.785 inches square I would invent a circular inch and do
A in circular mils is d square = 1 inch. What is the chance I would not fail? Even in 1750.
I have looked on the internet but could not find why such a measurement was created.
The decision to create circular mils was made long time ago, and I am interested if the
story behind it is known.


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## 480sparky (Sep 20, 2007)

Which number would you rather do the math with?


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## Magnettica (Jan 23, 2007)

Cletis said:


> How are the air pockets accounted for ?


They're there for air to pass through and cool the conductors. :thumbsup:


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## 123 (Oct 28, 2012)

480sparky said:


> Which number would you rather do the math with?


You can’t do math with circular mils using physics based formulas. The number has to be multiplied by
0.785 first to get the area in square mils.
There are interesting stories behind creating mathematical and physical measurements.
I can’t find any information on why circular mil was created and by whom.
Circular mils are used only in United states, and Canada.


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## Cletis (Aug 20, 2010)

123 said:


> Does anybody know why a circular mil area measurement was created,
> when square mil area would have been the logical choice of the times?


I think it was Everett Crosby around 1907 and an unknown mathmetician. not 100% on that yet though


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## Cletis (Aug 20, 2010)

YEs. It appears it was a quick and dirty convenience call the NEC made around 1907 because the area in circular mils equals the square of the diameter in mils anyhow, so, to uncomplicated things they just came up with circular mils/ft instead of the standard microohms x m (SI) units. just off the top of my head


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## 480sparky (Sep 20, 2007)

Cletis said:


> YEs. It appears it was a quick and dirty convenience call the NEC made around 1907.......


Negative. All my NECs back to 1895 have cmils.


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## Cletis (Aug 20, 2010)

480sparky said:


> Negative. All my NECs back to 1895 have cmils.


must have been brown and sharpe then in conjunction with the first president then (which quickly passed) to come up with quick easy formula to get the nec started and rolling with ampacity charts??


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## Cletis (Aug 20, 2010)

Magnettica said:


> They're there for air to pass through and cool the conductors. :thumbsup:


its called circle packing and it's a very serious subject


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## ponyboy (Nov 18, 2012)

Cletis said:


> its called circle packing and it's a very serious subject


I hope you get cancer


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## Cletis (Aug 20, 2010)

ponyboy said:


> I hope you get cancer


you have "issues"


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## ponyboy (Nov 18, 2012)

Cletis said:


> you have "issues"


You have cancer.


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## mbednarik (Oct 10, 2011)

I would assume that 250 mil stranded conductor has the same total cross sectional area in copper as 250 compact and solid. Probably take the area of the solid divide by 19, and that would be the area of each strand. Just a guess.


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