2 motors 2 AC units

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Bjenks

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East Coast of FL
I have two motors and two HVAC compressors (hermetically sealed) on a panel and trying to calculate the feeder. Would I do the 1.25% on the highest current of all 4 loads or would I do 1.25% of the largest motor and 1.25% of the largest compressor? I see some load calculation where it looks like the largest load rule is based on any motor load whether HVAC or a pump and others who destinguish between a pump/motor and a hermetic compressor.

Thanks
 
This could get tricky since the AC units will already have 125% added to their compressor load by the manufacturer on the nameplate. This will be listed as the minimum circuit ampacity. I'm unsure how you would factor that in to your calculation.
 
I would just add 25% to the largest motor or compressor.

Most AC units I've seen list both the amps they draw, and the minimum circuit ampacity. As Inifinity mentioned, the minimum circuit ampacity is just the ampacity of the unit with 25% of the largest motor current added to it. So you should be able to figure out which motor or compressor is the largest load.
 
msjeff said:
The answer to your question is in 440.33. It is not at all tricky.
Click to expand...

What if those motors are not associated with the AC units. Does 440.33 still apply? Say for example they are water pumps.
 
The article has no mention that the other loads- such as motors- need to be directly related to the operation of the compressors. There is an exception that states that if all the units are prohibited from running simultaneously then you can size the feeder a bit smaller. See exception no.1 for the exact wording.
 
msjeff said:
The article has no mention that the other loads- such as motors- need to be directly related to the operation of the compressors. There is an exception that states that if all the units are prohibited from running simultaneously then you can size the feeder a bit smaller. See exception no.1 for the exact wording.
Click to expand...

That is why in my first post I said that it can be tricky. Since he is sizing the feeder for a panel, does he use the MCA on each unit (which includes 25% for the compressor) or does he look at the FLA of the individual loads and size according to them?
 
You both are showing why I keep seeing it done both ways. A HVAC motor-compressor falls under 440 only if it is hermetically sealed, if it is not then the motor compressor falls under 430 which is for motors. I personally see 440.33 talking exclusively about motors as it pertains to a hermetically sealed motor-compressor. 430.24 is basically the motor equivalent to 440.33. The questions still remains should I include 430 and 440 loads together under 430.24/440.33?
 
I think the answer is treat the AC compressors just like a motor when doing a combination load, and add 25% to the biggest one. See 440.7 and its reference to 430.24.

It still isn't clear that a motor and a motor compressor are treated the same, but the exception helps to clarify that it does.
 
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