The use of Motor Capacitor"MFD" for microfarad is an older industrial marking, (usually withindustrial paints or inks) probably more common still with motor parts. the Greek mu will befound more often on modern audio and computer parts (silk screened or electrostatically printed).Part of the reason is that in older printing practises, special characters were rare and more expensive to set up. With modern printing (usually with computer generated graphics and fonts)there is no cost difference, or problems with availability of alphabets.

Millifarad Caps will be very large capacitors, and not always marked this way, but sometimes in Farads using decimal points. The important thing still with capacitors, even in motor applications is their duty voltage and surge voltage ratings, as well as making sure that the type of capacitor is the one recommended for the kind of job being performed in the circuit. Large caps tend to be electrolytics due to cost, but most electrolytics have fixed polarity and require minimal charging to form the insulating skin inside. A special breed of 'non-polar' electrolytic caps are made for audio (speaker) applications, usually simply by connecting internally a pair of caps in series with one reversed (+ve to +ve). This can allow the caps to handle A.C. signals without failures. 

In motors, current capacity and duty cycle is also important for prevention of failure. But if caps and motors keep blowing, it seems prudent to examine the load and the setup to see what is causing the failures

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