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How to derate a VFD based on Phase, altitude, and temperature

Here are the sizes for example:
1/2hp motor, 2.4 FLA 208/3/60 motor, 120/1/60 input
5.0hp motor, 15.5 FLA 208/3/60 motor, 240/1/60 input

Derating, in general, is a little misunderstood. If a motor and variable frequency drive is in the same relative environment, derating of the variable frequency drive is not required. If you have a 10hp motor and VFD at sea level and then move them to, say, 10,000 feet, they derate together, so they still work together.

In general, AC motors and drives are rated to 3300 feet in altitude and 40 degrees C. They both derate at about 3% for every thousand feet above that.

Operation above 40c also requires derating, usually 1% per degree above 40.

Using elevated carrier frequencies also requires derating because of the heat generated above minimum frequencies.

Single phase operation requires a derating factor of about 1.73 (square root of 3) because the INPUT current requirement goes up by not providing 3 phase power. If you are trying to operate a 5 hp motor and have single phase power, a 7.5 hp VFD drive would work marginally (1.5 times), a 10 hp VFD drive (2 times) would be preferred..

Check the user manual for the VFD you are using. They normally have charts for temperature and altitude derating.

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