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#### mikewillnot

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Existing McMansion with 120/240 has 2 identical trane units, labels below. For a dwelling service load calc, I'm looking for one number (per unit). This is a little bit greek to me, as it's been a few days since I took my license exam. Not for exam purposes, but for estimating available service capacity, I'm thinking I'm good if I take the minimum circuit ampacity (18.0 x 240), round up (4.5kva), and multiply by 2 (2 units).... call it 9kva. How far off am I?

#### SWDweller

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Power distribution and controls
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Your going to estimate the capacity by just the air conditioning? Me thinks you do not have a clue on how to do a load calculation.

Hint call the power company and get a years bills, look at the high KW and work from there.

#### micromind

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motors and controls.........
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I don't know the exact code but the unit will not draw more than 18 amps at either 208 or 230 volts.

I don't see a need to multiply by 2 but as I stated, I don't know the exact code here.

#### mofos be cray

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I don't know the exact code but the unit will not draw more than 18 amps at either 208 or 230 volts.

I don't see a need to multiply by 2 but as I stated, I don't know the exact code here.
He's multiplying by 2 because there's 2 of them.

#### micromind

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motors and controls.........
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He's multiplying by 2 because there's 2 of them.
I missed that completely........

#### mikewillnot

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Your going to estimate the capacity by just the air conditioning?
No, that would be stupid. I just asked a question about HVAC nameplate data. Everything else, I do not need to ask questions about.

#### farmantenna

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I don't think you have to, you can, use the MCA because it has added 25% to the motor load

#### wiz1997

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If I remember correctly.
Take the units LRA (locked rotor amps) multiply by 1.25 (largest motor) then add the amperage of the 1/3hp motor (found in the code book).
That should give you the value you need for that unit in your calculation if that motor is the largest in the building.
For the second unit leave out the largest motor multiplier.
This calculation will give the minimum required by the NEC.
If this is a test question using the 18 amp circuit value could possibly result in an incorrect answer.
The incorrect calculation could add VA to the total service calculation causing an increase in the wire size.
When taking tests, they are always looking for the MINIMUM allowed by code.

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