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[amps88]

Whats the difference between Kcmil and MCM?

 

[infinity]

Nothing. The Kcmil is a replacement for MCM. The use of the letter K to represent 1000 is more prevalent than the use of M so the term Kcmil became the new abbreviation.

 

[charlie b]

No, there is a difference. If a person writes or says ?MCM,? it means he or she is an old geezer, like myself. :grin:

I may be mistaken on this, but I think the ?M? in ?MCM? comes from the Roman Numeral System, in which that letter stands for 1000. If that is not right, my next guess is that the ?M? stands for ?mille,? the French word for 1000.

 

[celtic]

Here's a blast from the past:
MCM/KCM ~ [FONT=Verdana, Helvetica, sans-serif] posted December 19, 2005 12:09 AM[/FONT]

 

[NoVA Comms Power]

... I may be mistaken on this, but I think the “M” in “MCM” comes from the Roman Numeral System, in which that letter stands for 1000 ...

Correct, it's roots come from Latin "mille" -- for 1,000.

Today's most commonly used derivations use the "little m" for 1/1000th: millimeter, milliamp, milliliter, etc.

 

[danickstr]

latin does not use a "K" (all other letters but K) so kilo can't be latin, but IDK what language it comes from.

 

[infinity]

Here's what Wikipedia says:

"kilo-" means "thousand", coming from the Greek word χίλιοι ("khilioi") with that exact meaning. Examples of mostly rather commonly used words with the prefix "kilo" meaning a thousand times the unit are , kilocalorie (unequal to the nowadays rather used kilojoule), kilocycle aka kilohertz, kilogram aka kilogramme, kilolitre/kiloliter, kilometre/kilometer, kilostere for volumes of wood, kiloton aka kilotonne, kilovolt, kilowatt.

 

[NoVA Comms Power]

... "kilo-" means "thousand ...

Don't get me wrong, I'm of the opinion that the "correct" notation should be "k" ... I was just confirming Charlie's hunch about the roots of "M".

"k" is the generally accepted international metric "standard" for 1,000 ... while "little m" (milli) is properly used to represent 1/1,000th.

I suspect that when the NEC was "going metric" ... some well-meaning researcher confused "Latin" w/ "Metric" and used the "M" for 1,000 rather than the more correct "k"

Maybe I'll submit that as a proposed change for 2011. :wink:

Jim

 

[infinity]

The capital letter M was probably never correct (unless we're using Roman numerals) since it's an abbreviation for mega which is used to represent 1,000,000.

 

[NoVA Comms Power]

... it's an abbreviation for mega which is used to represent 1,000,000 ...

Absolutely right.

Here's the "correct" list of prefixes according to NIST ... and NIST is about as "authoritative" as it gets in the U.S.

Edit to add: I also thought that this official definition of an ampere was interesting:

[FONT=Myriad Roman,Syntax,Gill,Gill Sans,Arial,Helvetica]The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 x 10-7 newton per meter of length.[/FONT]

Jim