Conductor Labels

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The difference has to do with the age of the person using the descriptions. :grin:

Actually, they are the same thing. Both mean "1000 circular mils." I suspect that the "M" in "MCM" comes from the French word for one thousand. "MCM" is more familiar to the older generation (i.e., old guys like me :grin:).
 
Jack Winburn said:
Hello all:

Could you tell me the difference between MCM cable and KCMILL?

thanks
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There is none.

A few years back someone noticed the KCM means 1000 circular mils, when it should have been 100,000 circular mils ...and so MCM came to be.

Now my knowledge of roman numerals may be off, but that is the jist of it.


Here is real poop from the NECH:
The term MCM was defined as 1000 circular mils (the first M being the Roman numeral designation for 1000). Beginning in the 1990 edition, the notation was changed to 250 kcmil to recognize the accepted convention that k indicates 1000. UL standards and IEEE standards also use the notation kcmil rather than MCM.
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celtic said:
A few years back someone noticed the KCM means 1000 circular mils, when it should have been 100,000 circular mils. . . .
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Why would that be? :-? The "K" means 1000, the "C" means "circular," and the M" means "mils." So where would 100,000 come into the picture?
 
celtic said:
A few years back someone noticed the KCM means 1000 circular mils, when it should have been 100,000 circular mils ...and so MCM came to be.
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In 1990 the NEC decided to start using SI (international scientific notation), for all of its dimensional measurements. In effect this put the NEC on the Metric system, which uses Greek numerals for its prefixes, such as K (or sometimes k) meaning 1000 times.

So in AWG terminology "CM" meant area of the wire in circular mils, but this could easily be confused with the Metric system cm, or centimeters, meaning length (note the difference between capital and small letters). The correct SI abbreviation for the area of wire is "cmil", so the now the NEC uses Kcmil.

Of course you could choose to be like me; someone who says MCM but writes kcmil.:grin:
 
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Thanks for the insight. We are running some 350 as a main feeder and we have left-over spools of both MCM and Kcmil. I guess I am safe using both.....
 
For what it is worth, most people are pronouncing kcmil as a single word, kay'-cee-mill. By the way, in Hawaii, all the vowels are pronounced. It really seems strange for a while but you get used to doing it that way very quickly. Hawaii is pronounced ha-wah'-e-e. :smile:
 
Actually, it should be square mils instead of circular mils.
250 MSM is 11/16"
350 MSM is 13/16"
500 MSM is 15/16"
750 MSM is 1 5/32"
1000 MSM is 1 5/16"

~Peter
 
peter said:
Actually, it should be square mils instead of circular mils. . .
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I don't understand,
  • 110.6 states, "Conductor sizes are expressed in American Wire Gage (AWG) or in circular mils."
  • Table 240.92(B) A = conductor area in circular mils
  • Table 8 in Chapter 9 has a column header of circular mils
 
As is often the case, the Code [and in this case, the entire electrical industry] is in defiance of the rules of geometry and has it all wrong.
From the handbook:
"The circular mil area of a conductor is equal to its diameter in mils squared (1 in. = 1000 mils)."
Can you think of any ordinary wire that is square instead of round? I thought not. The formula is area = pi()*R^2. As an engineer, you should know that. I am right and everyone else is wrong.
~Peter
 
peter said:
From the handbook:
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peter said:
"The circular mil area of a conductor is equal to its diameter in mils squared (1 in. = 1000 mils)."
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Does the handbook really say that? If so, it gives us another good reason to not consider the handbook to represent truth. :rolleyes:

The McGraw-Hill Dictionary of Scientific and Technical Terms defines a circular mil as, "A unit equal to the area of a circle whose diameter is one mil (.001 inch)."

The area of that circle would then be given by Pi times (0.001) squared divided by 4 (in units of square inches).
 
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