Industrial Engineer · phase 9 of 16
Variable Torque Rating
Drive duty rating intended mainly for centrifugal fan and pump loads whose torque demand falls rapidly with speed.
The Explain card
- Plain English
- The variable torque rating is the drive's rating for centrifugal fans and pumps, whose torque demand falls with the square of speed. Because those loads never need heavy overload, the drive is allowed to run at a higher continuous current.
- Example
- The same drive that carries 40 amps constant torque is rated 50 amps variable torque. On a cooling tower fan that only ever starts unloaded, the 50 amp rating is honest.
- Why it matters
- Variable torque is the cheaper way to buy a drive for a fan or pump, and the wrong way to buy one for anything that can stall or start loaded. Ask what the load does at low speed before you take the discount.
- Hook
- A lighter duty for loads that go easy on the motor.
Where it sits in the deck
Phase 9: VFD Ratings, Sizing, and Motor Data
Nameplate arithmetic, where the currents, voltages and duty ratings decide whether a drive can actually run the motor you bolted it to.
