Help on this oddball

[winnie]

This 3 phase 240 v motor runs at 12 amps and T 430.250 shows 15.2 amps

So if the motor draws 12 amps on 3 phase then what would the draw be on the feeder which is single phase. Is this what @Dzboyce is talking about. The feeder would be drawing 28 amps based on 5 hp single phase motor?????

The VFD is a pretty efficient power converter, likely better than 95%. So the current into the VFD will pretty much be whatever is necessary to supply the true power consumption of the motor. The VFD supplies any reactive power needed by the motor.

Basically the input current to the VFD is almost completely disconnected from the current being consumed by the motor. Think 'transformer' where the primary and secondary current can be radically different, but with a VFD the transformation ratio can change.

If you are asking what the NEC requires, the circuit to the VFD must be rated based on the input capacity of the VFD, not any sort of calculation based on the connected motor.

Jon

 

[Dennis Alwon]

Thanks Jon, I was just trying to see if I do a vd calculation would I use the 15 amps or base it on the 28 amps of a single phase motor. It sounds like you are saying that I should use the 3 phase amperage.... 15 amps from the t. 250.150

 

[winnie]

You size the input circuit to safely supply 46A. This is the input rating of the drive.

You have two different voltage drop calculations: for the supply to the VFD, and from the VFD to the motor.

From supply to VFD you have a single phase system, sized on the basis of the current necessary to supply the power you expect the system to use.

For VFD to motor you use the 3 phase motor current.

Grundfoss probably has a table that tells you what size conductors to use.

-Jon

 

[Dzboyce]

Full load amps on the grundfos 5 hp 3 phase motor at 230 volts would be 17.4 amps. A single phase motor at 230 volts would have 25.7 full load amps. The vfd being used has an input rating of 46 amps.

Here's a link to the Grundfos Submersible Motor Guide. It has charts for wire size and distance to to allow for voltage drop. All the major sub motor manufacturers have equivalent manuals.

MS

Submersible motors for wells 4" and 6" diameter. Deep well applications for lifting and pressurizing water supply.

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