Sizing input protection for VFD converting single to three phase.

[blackbart10]

I am installing a Yaskawa VFD to drive a 3ph 208/230V centrifugal pump. Power source is single phase 240V. The VFD is rated for 42A 3ph. 240V load. The actual load is 18.4A 230v 3ph per motor tag. According to the manufacture chart for using the VFD as a phase converter I need AWG #6 copper conducter protected by a 80 amp slow blow fuse or a 100amp cb for the derated load for the input lines.
If I take the 3ph. load amps x 1.732 I get approx. 32 amps single phase. Do I actually need to the 100A cb or does a 40A sufffice?

 

[blackbart10]

https://www.yaskawa.com/delegate/getAttachment?documentId=AN.AFD.15&cmd=documents&documentName=AN.AFD.15.pdf

Here is the document. The chart is on page 9 of 12.

 

[ptonsparky]

I am installing a Yaskawa VFD to drive a 3ph 208/230V centrifugal pump. Power source is single phase 240V. The VFD is rated for 42A 3ph. 240V load. The actual load is 18.4A 230v 3ph per motor tag. According to the manufacture chart for using the VFD as a phase converter I need AWG #6 copper conducter protected by a 80 amp slow blow fuse or a 100amp cb for the derated load for the input lines.
If I take the 3ph. load amps x 1.732 I get approx. 32 amps single phase. Do I actually need to the 100A cb or does a 40A sufffice?

You can try the 40, it can’t more than not work. 42*1.73=72.6 is what you should use though.

 

[bwat]

Well for the conductors to the VFD, they need to be large enough to satisfy this:

430.122 Conductors — Minimum Size and Ampacity.
(A) Branch/Feeder Circuit Conductors. Circuit conductors
supplying power conversion equipment included as part of an
adjustable-speed drive system shall have an ampacity not less
than 125 percent of the rated input current to the power
conversion equipment.

And then there's also this to consider:

430.128 Disconnecting Means. The disconnecting means shall
be permitted to be in the incoming line to the conversion
equipment and shall have a rating not less than 115 percent of
the rated input current of the conversion unit.

 

[blackbart10]

You can try the 40, it can’t more than not work. 42*1.73=72.6 is what you should use though.

The 42A is the max rating for the VFD. Because of the required single phase derating I only have a 18.4A actual load

 

[ptonsparky]

The 42A is the max rating for the VFD. Because of the required single phase derating I only have a 18.4A actual load

Go for it. It may work. Nothing says you have to use the max.

 

[Dzboyce]

Been there, done this. Is this a 5 hp 230v/3ph motor? Your amperage doesn't quite meet 430.250 amperage. It will not run except under a very light load with a 40 amp breaker. You will need the 100 amp breaker for full load amperage. An Pentair Intelidrive or Franklin subdrive set up for 240 volt single phase in, 240 volt 3 phase out only needs a 60 amperage breaker. The yaskawa DOES need a 100 amperage breaker to accomplish the same thing. I have learned this the hard way.

 

[blackbart10]

Been there, done this. Is this a 5 hp 230v/3ph motor? Your amperage doesn't quite meet 430.250 amperage. It will not run except under a very light load with a 40 amp breaker. You will need the 100 amp breaker for full load amperage. An Pentair Intelidrive or Franklin subdrive set up for 240 volt single phase in, 240 volt 3 phase out only needs a 60 amperage breaker. The yaskawa DOES need a 100 amperage breaker to accomplish the same thing. I have learned this the hard way.

It is 7.5hp 230/208 3ph 3600rpm. The amperage is taken from the motor nameplate for 208v. Does this VFD run extremely inefficient or how/why does it use 100 amps 240v single phase to output 18 amps 208 3 phase?

 

[LarryFine]

Didn't Bwat answer this in post #4?

 

[Dzboyce]

You need to be using the amperage for 230 volt, not 208 volt. I've been there with a 5 hp submersible. I used a yaskawa because it was a few hundred dollars less expensive than a subdrive. This was for a pump for a mobile home and 5 acres of cherries. Everything was fine until they started irrigating. Then the 60 amp breaker kept tripping. 60 amps was what the subdrive would have required. The wire to the pump house from the mh pedestal was big enough for the 60 amp breaker. After 3 service calls, ended up pulling new wire from the mh ped to the pump house and installing the 100 amp breaker. Yeah, its that inefficient. I don't know if Franklin's Cerus VFD'S are as inefficient. I'm a Preferred Pump customer, not Headwaters.

Biggest I've installed like this is a 15 hp 230 volt 3 phase submersible set 6-700 ft deep. No three phase power available. They had to upgrade the entire service and main panel to accommodate the VFD.

Yaskawa is my vfd of choice for the Ag market. But I mostly use them 3 phase in/ 3 phase out. Most ag applications have 3 phase available. Its the residential applications that can be a problem.

 

[ptonsparky]

IIRC, I had a Problem a few years ago that when the original drive failed the replacement required a larger breaker. Something to do with the capacitors being used changed. 1Ph in 3 Ph out.