EC&M Tech Talk — Variable Frequency Drives — VFDs from Operation to Installation and Maintenance

In this EC&M Tech Talk, electrical code and safety specialist Randy Barnett takes a look at variable frequency drives – what we commonly call VFDs. The NEC, however, specifies requirements for adjustable speed drives (ASDs). An informational note in the Code definition explains that VFDs are one type of ASD. The terminology in the field is discussed including the concept of the motor soft start device. Understanding where the VFD fits into the world of motor controls is key for correct installation.

To perform installation and maintenance electrical workers should understand how the VFD works. While of great benefit for many applications, the VFD can also cause problems on both its input and output sides. These are discussed and what can be done to overcome these effects. Pay attention here and minimize spurious shutdowns!

Article 430 addresses motors and electronic motor controllers. Each subsection of Part X on ASDs is summarized and its intent explained. The Tech Talk wraps up with an overview of maintenance requirements found in the NFPA 70B, Standard for Electrical Equipment Maintenance. While maintenance is mandated by the standard, electronic drives are not directly mentioned in the standard but fall under motor controller maintenance requirements. Practical maintenance items are discussed.

VFDs are reliable and energy efficient devices meeting many specific motor control needs in industry. They must be installed per code and manufacturer’s instructions and maintained for maximum energy efficiency and to minimized downtime. This Tech Talk helps explain those requirements.