MOCP 125% of MCA for HVAC Equipment??

[jobuTupaki]

Curious how the manufacturer came to these values, but I am trying to work out the calculations and verify. Below is for an AC system

Below is for a rooftop unit:


I am curious as I usually use the horsepower of the unit/motor to find the FLC, from there I calculate MCA = 1.25*FLC, and then size the breaker at FLC*2.25. However, none of the mechanical units I am dealing with reflect those calculations.

I am fine using the manufacturer's recommendations, but I usually crosscheck to make sure everything looks right.

 

[paulengr]

Curious how the manufacturer came to these values, but I am trying to work out the calculations and verify. Below is for an AC system
View attachment 2560916
Below is for a rooftop unit:
View attachment 2560917

I am curious as I usually use the horsepower of the unit/motor to find the FLC, from there I calculate MCA = 1.25*FLC, and then size the breaker at FLC*2.25. However, none of the mechanical units I am dealing with reflect those calculations.

I am fine using the manufacturer's recommendations, but I usually crosscheck to make sure everything looks right.

Compressors often require a lot of starting torque. So you will see goofy things like say a 100 HP compressor with a 150 HP motor or a “100 HP” motor but with a crazy nonstandard service factor like “1.40”. The latter is just so that end users see a “100 HP compressor”. Plus they have the actual known LRC.

So trying to predict name plate information on a compressor using article 430 is not going to work.

 

[infinity]

Curious how the manufacturer came to these values, but I am trying to work out the calculations and verify. Below is for an AC system

Looking at the fan FLA and the compressor RLA the MCA and MaxOCPD numbers seem to be too high.

 

[RWC/NC.]

Article 440.
440.22(A) Rating and setting of Individual Motor-Compressor.
A rating or setting, not to exceed 175 percent (it can be less than 175%)
* if not sufficient for the starting current of the motor, the rating or setting shall be permitted to be increased but shall not not exceed 225% of the motor rated load current or branch-circuit selection current, which ever is greater.

 

[jobuTupaki]

Thank you, all. Sometimes I think too hard.