HVAC Actual Power Draw

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Outside the US, there is definitely full three phase power, particularly for large motors. Not common at all in residential, even for A/C AFAIK.
 
jaggedben said:
Sorry, but what exactly does '2-out-of-three phases' mean here? Do they have equipment that actually draws power from two L-L voltages and not a third, like ours? Or are we just talking about using two out of three available line conductors? I don't see how you get 4-phase from the former convention.

I've always maintained that conductors should be labeled L1, L2, etc and that 'phase" should be used only to refer to a combination of two line conductors. I recognize not everyone is on board with that. But as this example shows the alternatives just really don't make any sense.
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I used the term "2 out of 3" to distinguish it from "2 phase", because in other parts of the world, they use the term 2 phase to describe equipment that draws power from two L-L voltages. We do exactly the same here, but WE call it "single phase" (because it is). Using the term "2 phase" for this would be MORE confusing for us, because we actually HAVE a real "2 phase" system still in use. Not a lot, but it does still exist. So people here get confused when they see Europeans use the term "2 phase", because that term means something different to them than it does to us.
 
electrofelon said:
Or use 66% of the MCA 😉
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Well, close enough! If the built-in thermal protector of a "hermetic" compressor is set at 125% before it trips plus the provision of 125% in the MCA formula, you'll get 1.25^2 = 1.56. That would be the inverse of 0.64. Your use of 0.66 is on the safe side!
 
Unlike other section of the NEC, Section 440 deals with Hermetic Refrigeration Motor Compressors. That's makes it unique, the suction refrigerant cools the motor, which makes it more efficient. The label information on the HVAC unit must be used, and disregard other sections of the NEC.
 
mtnelect said:
Unlike other section of the NEC, Section 440 deals with Hermetic Refrigeration Motor Compressors. That's makes it unique, the suction refrigerant cools the motor, which makes it more efficient. The label information on the HVAC unit must be used, and disregard other sections of the NEC.
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The hard part for us is getting valid load information early enough in the project to do electrical load calculations. We can't wait until the nameplates are on the job site. If we use MCA as the load amps, we are being conservative and if there is a lot of equipment, too conservative. When your equipment sizes jump in intervals of 100, 200 or 400 amps, you don't want it to jump too soon.

It's not hard to get the RLA for compressors and FLA for fans. The hard part is knowing what to ask for, and finding someone who understands the question.
 
JoeStillman said:
The hard part for us is getting valid load information early enough in the project to do electrical load calculations. We can't wait until the nameplates are on the job site. If we use MCA as the load amps, we are being conservative and if there is a lot of equipment, too conservative. When your equipment sizes jump in intervals of 100, 200 or 400 amps, you don't want it to jump too soon.

It's not hard to get the RLA for compressors and FLA for fans. The hard part is knowing what to ask for, and finding someone who understands the question.
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Best to specify the details and take off data from the mechanical plans. I have done it and it never failed me.
Consider HVAC as a pump, a heat pump. Once you see the typical values of EER of all equipment in the market plus the cooling capacity as specified by the mechanical guys, you won't miss your estimates. The good thing is that HVAC sizing puts you on the safe side if you happen to undersize the unit you buy. The units will just run longer (longer cycle time) which in effect prevents the suspended water vapor from condensing at the coils thereby minimizing your problem of getting your units better drained of condensations.
 
To add to the confusion

  1. Three Phase, 4 Wire, 240 Volt, Delta Service:
    Three phase, 4 wire (grounded neutral), 240 Volt delta connected service is only allowed by special permission where two phase distribution is available. If three phase distribution is available, wye connected service must be taken.
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And that is straight from the PP&L website

Rule 2

Rule 2
www.pplelectric.com www.pplelectric.com
 
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