Derate Three Phase VFD for Single Phase Power

There are many customers who want to derate their three phase Variable Frequency Drive (VFD) for single phase power.

Some manufacturers offer products that are designed for single phase input, three phase output. The products that are available for single phase input, three phase output max out at 3hp or 5hp. If the electric motor available is three phase and is larger than 5 horsepower, and only single phase power is available, you’ll have to derate the three phase VFD for single phase power.

The formula we use to derate variable frequency drives for single phase power is as follows: AC electric motor current multiplied by 1.73, then size three phase (vfd) variable frequency drive with the corresponding amps. Most times to derate a three phase VFD for single phase power can be done by going up one size. Typically, a 10hp three phase motor would need at least a 15hp or 20hp vfd in order to run off single phase power.

For example. Lets say I have a 7.5hp motor that pullsapproximately 23 amps; I want to use a vfd, however I only have single phase 230V line voltage. I need to multiply the 23 amps by 1.73 which gives me the new revised current (39.73 amps) Now I know I need a three phase 230V drive that is rated at40 amps or higher.Avfd that is rated at approximately 40 amps is about 15hp,and for this particular application would run a 7.5hp 240V driveperfect on 240V single phase power.

Precision Electric, Inc highly recommends contacting someone with experience to safely install variable frequency drives and/or electric motors. Call Precision Electric today to derate a three phase vfd for single phase power.


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