I am connecting up an AC motor and was wondering if this labeling system was representative of something? Or just another set of letter like X,Y,Z?
I could not find any information regarding this in IEC 60034-8, Rotating electrical machines – Part 8: Terminal markings and direction of rotation or a brief search of google, forums etc.
Answer
The letters are "representative of something"
To assist in providing an international standard the International Electrotechnical Commission (IEC) created that IEC 60034-8 standard. "Terminal markings and direction of rotation"
An electrical machine compliant to 60034-8 will ensure that clockwise rotation of the drive shaft will occur for positive electrical phase sequence U-V-W.
Thus if you were to wire such a machine upto a distribution labeled A-B-C and these electrical phases were A leading B, leading C... you would have the expected mechanical rotation
is it "just another set of letters"? you could say they arbitrarily chose that sequence, a sequence that is just as good as any other BUT they assigned a specific meaning to it and a meaning that is internationally recognised.
MotorA from supplier A and MotorB from supplier B being compliant to this reg & meeting the customer requirements would be drop-in replacements that would minimise any unexpected mechanical rotation
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