When you get the call, “The motor won’t start,” you’d best have a logical and systematic plan in place to approach the problem. “Easter egging” just doesn’t work unless you happen to be very lucky!

In Part 1 of this two-part series, we presented a 3-phase, 480VAC motor circuit with its associated controls (Figure). We stepped through a logical, systematic approach to troubleshoot the main power ...

In the ac-induction motor-control system in Figure 1 , the servo loop is a PWM drive circuit. The circuit switches the MOSFETs, which in turn send current through the legs of the ac motor. A typical ...