More and more often, variable frequency drives (VFDs) are used for control of fans and compressors in HVACR systems. The benefits are well documented and industry acceptance is such that most electric ...

A Variable Frequency Drive (VFD) regulates the speed of a 3-phase AC electric motor by controlling the frequency and voltage of the power it delivers to the motor. These devices, also known as ...

All questions and answers are based on the 2011 NEC. Q. What is the Code rule for motor control circuit overcurrent protection? A. Motor control conductors that aren’t tapped from the branch circuit ...