UL508A Supply Ratings Question

[CADMonkey]

In my searches I have found many answers that are not really answers.

In a multiple motor control panel using VFD's, do you use the VFD Input rating or the Motor FLA for calculating total FLA?
This panel is not my design but is a customers design.
Here are the "loads": (All are 460VAC 3-phase other than the CPT which is line to line on two of the legs)
VFD1=246A running a motor with 135 FLA
VFD2=106A running a motor with 45 FLA
VFD3=46A running a motor with 23 FLA
AC Unit=3.14 FLA
Control Power Transformer 3000VA @ 460VAC=6.52 FLA

UL508A states that in all calculations involving amperes, calculations resulting in fractions shall be rounded to the nearest whole number.

Is the "total FLA" of this panel 408FLA or 213FLA?

To me it makes sense to use the VFD Inputs because there is no guarantee to me that they will actually use the motor(s) that is(are) on the drawing or that they won't upsize the motor(s) at a future time if they discover that it(they) is(are) not strong enough for their application.

I would ask that you don't dance around the question with hypotheticals or irrelevant questions. This seems like simple math to me and there should really only be one answer unless there is a clear and concise description as to why it would need to be more complicated.

 

[petersonra]

49.2 The full-load ampere rating of the panel shall, at a minimum, include the sum of the ampere ratings
of all loads that are able to be operated simultaneously plus the primary ampere rating of all control
transformers connected to the input voltage.

Seems pretty clear that you need to use the input rating of the VFDs.

 

[CADMonkey]

Seems pretty clear that you need to use the input rating of the VFDs.

I think my customer would argue that the actual load is what the motor is drawing which, in this case, is significantly less. What section of the UL508A could I use to refute that argument?

 

[petersonra]

I think my customer would argue that the actual load is what the motor is drawing which, in this case, is significantly less. What section of the UL508A could I use to refute that argument?

Look at 49.2. clearly says use RATINGS of loads, not actual loads.

 

[Jraef]

Look at 49.2. clearly says use RATINGS of loads, not actual loads.

Yes, but I’ve always interpreted that to mean that you cannot use the actual measured current draw of a motor (something people try to do all the time), you must use the rated FLA on the motor nameplate.

To me, the VFD is not a load, it is a controller for a load. If you had a 125HP motor, would you use the max amp rating of a NEMA sized 5 contactor that is based on a 200HP motor? No, you would use the FLA of the 125HP motor.

You can’t be held responsible for what a user might do in the future. If your nameplate says 213A, that is based on the load it was designed for. If they someday decide to increase the sizes of the motors, they would have to change the OCPDs, feeder circuit etc. and would thereby be ignoring the listing and labeling of the panel, which would be a 110.3(B) violation.