What does the acronym MCM stand for?

I assume you are looking for the meaning of this acronym.

M = thousands

CM = circular mils

CM is the cross-sectional area of wire whose diameter is measured in MILS

One MIL = One-thousanth of an inch

A lesser ussage is KCM, where K = thousand

Common MCM sizes in the electrical trade are 500, 350, 250 Additional Answer First of all, 'MCM' isn't an acronym; its an abbreviation. 'Acronyms' are words formed from abbreviations, so must be pronounceable which, clearly, 'MCM' isn't!

A circular mil (CM) is a figure that represents the cross-sectional area of a circular-section conductor whose diameter is one mil (i.e. one-thousandth of an inch).

It's important to understand that a circular mil doesn't actually measure cross-sectional area, it merely a figure that represents a cross-sectional area. This is because 'squaring a diameter' doesn't result in a unit of area unless the ratio 'pi' is taken into account (because area = pi x radius2).

To confuse matters further, 'M', in this rather-odd system of measurement, represent '1000' rather than the more-usual 'k'.

Interestingly, the circular mil is a measurement unique to North America. Elsewhere in the world, conductor sizes are measured in square millimetres.

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I suppose that MCM is the incorrect acronym for micrometer.

The micrometer is unit of length, with the symbol μm; the value is 0,000 001 m.