Variable frequency drives can present a shock hazard to workers and users.
When a drive is energized but disabled, and the motor is stopped, it’s NOT open…there is no air between the line voltage and the motor leads. To safely work on the motor, the line input to the VFD must be opened. Some newer drives have a feature called “safe torque off,” which also is NOT a contractor. When the “safe torque off ” is active and the motor is stopped, the power connection is NOT open…there is no air between the line voltage and the motor leads. To safely work on the motor, you must open the line input to the VFD. “Safe torque off ” simply interrupts the gate power to the output transistors so that rotation is not possible. The transistor and the diodes still connect the
motor leads to the line voltage, which can cause a shock hazard unless the line input to the VFD is opened.
At Invention House we take great precaution when building and working on VFDs because of these conditions.
Consult the users guide, website FAQ page or the help center of your VFD manufacturer before working on any VFD.
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