We are building a system which will have 3 motors (2 hp each) operating off of one VFD. They will be about 100 - 150 ft. away from the VFD and I need to know if it is ok to only rely on the VFD for overload protection.

My goal is to run only one power cable out to the motor location and then split it at a junction box. Obviously, having separate overloads at the VFD control panel would require three separate power cables to the three motors. Relying only on the VFD to kick out for a overload situation is the simplest solution. Please advise...

 

> We are building a system which will have 3 motors (2 hp each) operating off
> of one VFD. They will be about 100 - 150 ft. away from the VFD and I need to
> know if it is ok to only rely on the VFD for overload protection.

No, if that worked, people would NEVER use one overload per motor, they'd just cover the entire panel with one overload relay.

> My goal is to run only one power cable out to the motor location and then split
> it at a junction box. Obviously, having separate overloads at the VFD control
> panel would require three separate power cables to the three motors. Relying
> only on the VFD to kick out for a overload situation is the simplest solution. Please advise...

It's simple because it doesn't have enough parts to do the job. How is the VFD going to know if only one of the motors gets jammed? If the other two are operating at FLA, that one is going to have to hit 175% to bring the total to 125% or whatever the limit is. It's even worse if the other motors are operating at part load or if one motor somehow becomes disconnected. Why couldn't you just put the correct number of overloads at the far end of the cable and run control conductors back?

Also, when running multiple motors off one VFD, you don't want to enable sensorless vector or any advanced control modes, because the multiple motors will confuse the control algorithm. Put it in the dumbest mode available.

 

If you are in the US, this would not meet code which generally requires individual overload protection for each motor.