Motor MCA to HP 1

[mikefinn]

Can someone confirm if my calculations are correct?

I was given only the MCA of a chiller (571.3), it is applied at 480V and I want to convert MCA to HP.

I divided the MCA by 1.25 to get 457A (assume this is the FLA).

HP = V*I*eff*1.73*pf/746

I assumed eff=0.85 and pf=0.8 to get 345hp.

This is all new equipment. Thanks.

 

[dpc]

Assuming there is only one motor on the chiller skid, you are probably in the ball park. If there are multiple motors, the MCA will be the sum of all motors plus 25% of the largest, IIRC.

But as an electrical, you should just leave it in kW and leave the hp nonsense to the flangeheads.

"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)

 

[wareagle]

The MCA is the minimum circuit amps for the conductor. It is not the FLA of the compressor. You should also have the Minimum OC device listed.

 

[jraef]

You should also have the Minimum OC device listed.

Ahhh... if only that were true. I have seen numerous installations where there is in fact NO other information other than the MCA. Sometimes the end user will write down the motor RLA with a felt pen on the inside of the enclosure door, usually because they weasel it out of a chiller service tech. I don't know why they get away with not providing full disclosure of technical data, but for some reason the Chiller industry seems to. I think it's because they want to provide the servicing and replacement of components, so they tightly control the information, figuring that all the installing electrician needs to know is MCA to size the conductors and MOCP to size the circuit protection device.

But your formula is probably good enough, depending on why you want HP as a value (it's not something you would use in equipment selection for instance). I just looked at one where the 4160V motor was 43 RLA (a rare one where they provided it) and the MCA was 55A, so if you divide the MCA into the RLA, you get a value very close to what your formula would have provided.

But keep in mind, there is a difference between RLA vs FLA and actual maximum HP capacity of the motor (if it were stand alone) would be based on FLA, not RLA. RLA would be for the motor and chiller as a combo which, in the case of a chiller where they are usually integral, is probably more relevant to what you need for something like an energy study.

I'd be interested to hear why you want a HP value.


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[mikefinn]

Thank you all.

Jraef, you are correct all that is provided is the MCA value on the chiller.

I am performing a SC/Coor/AF study on the facility and my software requires a HP or kW rating. The chiler will slightly affect my SC results and could change an IE level in my AF analysis.
Thanks.