MCA is 200% of FLA for condenser unit

[victor.cherkashi]

I need to supply power to a roof-mounted 5-ton Mitsubishi condenser unit, which includes one compressor with a FLA of 19A and two fans, each with FLA of 0.8A. The unit operates at 208/230V, single-phase, MCA = 40A and MOP = 45A. I was curious why the MCA is 200% of the FLA, so I reached out to technical support for clarification.

Mitsubishi's support explained that the compressor current listed in the specifications is based on standard operation at 230V. For operation at 208V, you should add 20% to the FLA. In extreme weather conditions (0°F for heating or 115°F for cooling), the current can increase by another 40%, which is why the MCA is set at 40A.

Since the building's system is 208V three-phase, I need to account for 34.6A per unit, calculated as (19 + 0.8 + 0.8) * 1.2 * 1.4 = 34.6A. Multiple units like these connected to the same panel will significantly increase the size of the feeder and panel.

This is the first time I've seen such a large discrepancy between MCA and FLA.
WHO gave them an idea for the exclusion of the 40% current increase from the FLA for extreme weather conditions.? What if 115°F temperatures last for 5 hours or more?

I would appreciate your thoughts on this matter.

 

[topgone]

My take on the matter:
The power draw of the compressor at 230V = 19 X 230 = 4,370 VA. The power draw of the fans at 230V will also be = 0.8 X 230 = 184 VA.
When used at 208V, the compressor draws = 4,270/(208 X 0.7PF) = 30A while each fan draws = 184/(208 X 0.7PF) = 1.26A, each (0.7 PF typical of 1-phase motors).
MCA= 1.25 X 30 + 2 X 1.26 = 40A. Hope I didn't muddle the situation.

 

[wwhitney]

The power draw of the compressor at 230V = 19 X 230 = 4,370 VA. The power draw of the fans at 230V will also be = 0.8 X 230 = 184 VA.
When used at 208V, the compressor draws = 4,270/(208 X 0.7PF) = 30A while each fan draws = 184/(208 X 0.7PF) = 1.26A, each (0.7 PF typical of 1-phase motors).

Your computation is correct only if the PF at 208V is 0.7 times the PF at 240V. If the PFs are the same, you can leave the PF out entirely, or you should include it in both calculations, where it will cancel.

Cheers, Wayne

 

[victor.cherkashi]

My take on the matter:
The power draw of the compressor at 230V = 19 X 230 = 4,370 VA. The power draw of the fans at 230V will also be = 0.8 X 230 = 184 VA.
When used at 208V, the compressor draws = 4,270/(208 X 0.7PF) = 30A while each fan draws = 184/(208 X 0.7PF) = 1.26A, each (0.7 PF typical of 1-phase motors).
MCA= 1.25 X 30 + 2 X 1.26 = 40A. Hope I didn't muddle the situation.

I've conducted online research, I believe the FLA rating on a motor's label incorporates power factor, efficiency, and applied voltage.
FLA = (HP × 746) / (√3 × V × PF × efficiency).

 

[victor.cherkashi]

The unit to be installed is a variable refrigerant flow (VRF) type. One reason I suspect the high MCA is due to the presence of an internal VFD. Low-quality VFDs generate significant harmonics, which can increase the current drawn from the building's system by dozens percent. Take a look at the attached screenshot of a VFD drive that was part of my project last year—you can see the difference between input and output KVA.

Another possible reason for the high MCA could be a game with numbers to achieve a higher 'Energy Efficiency' rating for energy code compliance.