The above Ad will no longer appear after you Sign Up for Free!
Discussion in 'Question of the Day' started by derekleffew, Oct 11, 2008.
When discussing wire sizing, "kcmil" means the same thing as "MCM," correct?
That is correct.
MCM – Thousand Circular Mils. “M” for “thousand”. (Ah, the good old days, not “M” for “mega”, and when “MM” was “million”.) C for, well, Circular. And M for mil, or 1/1,000 inch. And it’s essentially an area concept, but with a unit of length. Now that’s an Imperial unit.
kcmil – “k” for “kilo” (1,000), “c” is still circular, and “mil” is still “mil” (1/1,000 inch). Metric prefix attached to an Imperial unit. Elegant.
1000 C 1/1000. One-thousand one-thousandths. Wouldn't that be ONE? But 500 MCM is not 500 square inches; I don't think it's one-half square inches either, though that's closer.
this web site:
MCM is thousand circular mils. Circular mils is a measurement of area:
1 CM = .000001 square inch.
1 MCM = .001 square inch.
So 500 MCM wire has an area of approx. 0.5 or 1/2 square inch, but according to the chart, it has a nominal diameter of 0.813 inches.
To answer your question, kcmil does equal MCM (one kilo of circular mills does equal 1,000 circular mills).
Like I said, it's a peculiarly defined unit: The mil is length, but MCM or kcmil is area. So you can't mutiply the M (1,000) by the 1/1,000 to get 1. Worse, I have two conversions for this, the one in the link that philhaney provided, but another in an engineering handbook. A circular mil is either 0.000001 square inch per the philhaney link, or 7.854x10^-7 (or 0.0000007854) square inch per Perry's Handbook. The latter rounds to the former, though.
From "engineeringtoolbox" website:
A circular mil is the equivalent area of a circle whose diameter is 0.001 (10-3) inch, or approximately 0.7854 millionths of a square inch.
Separate names with a comma.