Mechanical Load KVA

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Easy question first. For simple motors like your exhaust fan, 430.6(A)(1) tells us to ignore the nameplate and use one of the tables listed. For a 460 volt, 2 HP motor, table 430.250 gives us a full load current of 3.4 amps. There is some debate over whether the next part should use 460 or 480 in the calculation. I use 480 to be conservative. 480 volts times 3.4 amps times the square root of 3 gives a result of 2.83 KVA.

Now the trickier part. The term ?RTU? can mean several things. ?Return Terminal Unit? is one of them. But I think they mean ?Roof Top Unit.? Even so, that phrase can mean a simple fan or a complex system or packaged unit that includes several motors, and might even include equipment that runs a compression cycle. Given only the input information you have supplied, I would use the MCA value as the maximum current that the system would draw. The calculation would then be, 480 volts times 193.35 amps times the square root of 3 gives a result of 160.7 KVA.

 
Thanks Charlie. I appreciate your response which clarifies this significantly.

I reviewed other posts regarding the 460 vs. 480 debate (which you also posted great responses) but I still wasn't sure what to do with the Roof Top Unit.
 
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