How do you size a circuit breaker for a VFD?

On VFDs you are required to have the feed conductors sized at a MINIMUM of 125% of the VFD’s maximum rated amps, the motor is NOT factorerd into it. So if you have a VFD rated for 100HP but it is connected to a 50HP motor, you MUST size the conductors for the max amp rating of the VFD, not the motor.

How is VFD size calculated?

Multiply the motor FLA by two and select a VFD rated for twice the motor’s FLA. For example, if you have a 10 HP motor with a FLA of 28 amps, you’ll need a VFD rated more than 56 amps and around 20 HP. For small shops or home use, keep in mind that VFDs are the number one power polluters on the planet.

Can you oversize a VFD?

An oversized VFD can be used for a smaller HP motor. The advantage of this application is that if the motor requirements increase, the VFD may be large enough to still handle the increased load.

How do you prevent VFD from tripping GFCI?

Another method is to disconnect the motor. If doing so prevents the GFCI from tripping the contributing source of leakage current is most likely from the output stage of the VFD. However, most often than not, the GFCI is tripping from a combination of the two and improvements on both the input and output will help.

Can you put a VFD on a single phase motor?

People often wanted to run the motors at reduced speeds so they asked, “Is it possible to add a VFD to my single phase motor?” In general, single-phase motors cannot be run with VFDs. However, it is possible to input a single-phase to a VFD and output variable voltage to a 3-phase induction motor.

What size breaker should I use?

How do I size a breaker? Generally, you should size a breaker for 125% of the load (or 25% extra capacity) and no less. Oversized breakers can allow wires to heat above safety levels without stopping the current. On the other hand, undersized breakers may continuously trip under normal operation.

Do VFDS have fuses?

Variable Frequency Drive manufacturers no longer include fuses inside their device to help protect their products. Without the protection of a fuse with your VFD, you run the risk of dealing with nuisance tripping or even outages.