Motor Class

This refers to the temperature rise of the insulation above ambient. The difference in temperature is the same in either degrees Kelvin or Celsius. The K does indeed mean kelvins.

As a sample, 90 deg Kelvin = minus 183.15 deg C. So this just cannot be. Tornado, pls re-evaluate. The K must mean something else. Cannot be kilo-ohms either. Assuming that K stands indeed for kilo, this would make 90K = 90000. This is neither here nor there. Anyway, classes of insulation for electric motors are well covered, including max permissible temp rise, in K or C, makes no difference. So why not just take it from there and be done with it.

The K is exactly what I said it was. It is about temperature difference, not absolute temperature from zero. Since 1K = 1°C precisely, this works just fine.

Incidentally, the term "degrees Kelvin" (or °K) is now obsolete. It is now just "Kelvins" (or K), with neither the word nor symbol for "degrees."

Yours sincerely--Editor Crankshaft

This little interchange with you, editor, was very illuminating and informative. Not quite what I expected, perhaps, but informative nevertheless.

It is already answered – here is additional clarification:

In terms of temperature difference:

1 K = 1 °C = 1.8 °F = 1.8 °R (all indicate same amount of change of temperature)

But in terms of temperature level (scale):

273.16 K = 0 °C = 32 °F = 0 °R (all indicate same level of temperature – freezing level)

See http://en.wikipedia.org/wiki/Kelvin or http://en.wikipedia.org/wiki/Celsius

Also note in the wikipedia link 'the kelvin is not referred to as a "degree", nor is it typeset with a degree symbol; that is, it is written K and not °K'.

So, 1 K = 1 °C, 65 K = 65 °C, 80 K = 80 °C, 90 K = 90 °C and so on ….

- MS