load calcs a/c

[normbac]

I was trying to figure load calcs for a 3 phase 208v a/c unit the only info I have is the MCA which is 65A can I use this as actual load, not sure how to do this as far as wattage per phase any info would be helpful since I am clueless about putting this to paper. :? TIA

 

[bob]

The MCA is the minimum circuit amps. This give you the conductor size for the unit. You should also have Max Breaker size listed.
What else do you need?

 

[normbac]

I was asked put to put load calcs on paper so I wasnt sure if you could use the mca as actual load On a b c column of load calcs I wasnt sure what to put as wattage in each column

 

[normbac]

might not be clear I know 208x65x1.73 but not sure if minimum circuit amps is correct to use for calculating a panel load I guess the word minimum is what is confusing me

 

[hmspe]

You really need the compressor running load amps and the outdoor fan and indoor fan full load amps to calculate what goes in the panel. Using MCA for the panel load will give an inflated panel load if there is more than one A/C or if the A/C compressor is not the largest motor on the panel. There is no way to calculate running load from the MCA and MOCP values.

 

[normbac]

You really need the compressor running load amps and the outdoor fan and indoor fan full load amps to calculate what goes in the panel. Using MCA for the panel load will give an inflated panel load if there is more than one A/C or if the A/C compressor is not the largest motor on the panel. There is no way to calculate running load from the MCA and MOCP values.

Thanks for info this is what I found on unit can you explain what numbers I would actually use Thanks again

[FONT=Times New Roman, serif]Voltage[/FONT]	[FONT=Times New Roman, serif]208V 3Ph[/FONT]	[FONT=Times New Roman, serif]SupplyFan FLA[/FONT]	[FONT=Times New Roman, serif]16.7 (amp)[/FONT]
[FONT=Times New Roman, serif]Frequency[/FONT]	[FONT=Times New Roman, serif]60 (Hz)[/FONT]	[FONT=Times New Roman, serif]CondensingUnit FLA[/FONT]	[FONT=Times New Roman, serif]4.8 (amp)[/FONT]
[FONT=Times New Roman, serif]System MCA[/FONT]	[FONT=Times New Roman, serif]65.0 (amp)[/FONT]	[FONT=Times New Roman, serif]CondenserFan Power[/FONT]	[FONT=Times New Roman, serif]830 (W)[/FONT]
[FONT=Times New Roman, serif]System MOCP[/FONT]	[FONT=Times New Roman, serif]80 (amp)[/FONT]
[FONT=Times New Roman, serif]Compressors RLA[/FONT]	[FONT=Times New Roman, serif]38.0 (amp)[/FONT]
[FONT=Times New Roman, serif]Cooling FLA Total[/FONT]	[FONT=Times New Roman, serif]59.5 (amp)[/FONT]
[FONT=Times New Roman, serif]Unit Oper Range-Nom Voltage[/FONT]	[FONT=Times New Roman, serif]+/- 10%[/FONT]

 

[jrohe]

Thanks for info this is what I found on unit can you explain what numbers I would actually use Thanks again

[FONT=Times New Roman, serif]Voltage[/FONT]	[FONT=Times New Roman, serif]208V 3Ph[/FONT]	[FONT=Times New Roman, serif]SupplyFan FLA[/FONT]	[FONT=Times New Roman, serif]16.7 (amp)[/FONT]
[FONT=Times New Roman, serif]Frequency[/FONT]	[FONT=Times New Roman, serif]60 (Hz)[/FONT]	[FONT=Times New Roman, serif]CondensingUnit FLA[/FONT]	[FONT=Times New Roman, serif]4.8 (amp)[/FONT]
[FONT=Times New Roman, serif]System MCA[/FONT]	[FONT=Times New Roman, serif]65.0 (amp)[/FONT]	[FONT=Times New Roman, serif]CondenserFan Power[/FONT]	[FONT=Times New Roman, serif]830 (W)[/FONT]
[FONT=Times New Roman, serif]System MOCP[/FONT]	[FONT=Times New Roman, serif]80 (amp)[/FONT]
[FONT=Times New Roman, serif]Compressors RLA[/FONT]	[FONT=Times New Roman, serif]38.0 (amp)[/FONT]
[FONT=Times New Roman, serif]Cooling FLA Total[/FONT]	[FONT=Times New Roman, serif]59.5 (amp)[/FONT]
[FONT=Times New Roman, serif]Unit Oper Range-Nom Voltage[/FONT]	[FONT=Times New Roman, serif]+/- 10%[/FONT]

Your calc would be (59.5 amps x 208 volts x sqrt(3)) + 830 watts = 22,265.9 VA (round up to 22,266 VA).

 

[normbac]

Your calc would be (59.5 amps x 208 volts x sqrt(3)) + 830 watts = 22,265.9 VA (round up to 22,266 VA).

Thankyou

 

[mull982]

Your calc would be (59.5 amps x 208 volts x sqrt(3)) + 830 watts = 22,265.9 VA (round up to 22,266 VA).

Is this because this 59.5 is given for the full load amps of all fans, motors, etc.. running in the cooling unit?

I guess you want want to use this kW (or VA) vaule in a panel schedule because the MCA has an additional factor on it that is not necessary to include in the load calculation of the panel but rather is just for correct sizing of the circuit to the A/C unit?

 

[jrohe]

Is this because this 59.5 is given for the full load amps of all fans, motors, etc.. running in the cooling unit?

Yes, the 59.5 amps is the sum of the 38.0 amp compressor, the 16.7 amp supply fan, and the 4.8 amp condenser fan.

I guess you want want to use this kW (or VA) vaule in a panel schedule because the MCA has an additional factor on it that is not necessary to include in the load calculation of the panel but rather is just for correct sizing of the circuit to the A/C unit?

Correct. Typically, the MCA is the full load current of the largest motor x 125% plus the full load current(s) of the remaining motors. Because the MCA adds 25% to the largest motor, the MCA is not indicative of the actual load of the equipment. The MCA is used strictly for sizing the conductors to the equipment.

 

[david luchini]

Yes, the 59.5 amps is the sum of the 38.0 amp compressor, the 16.7 amp supply fan, and the 4.8 amp condenser fan.

So why add 830 watts for the condenser fan if the 4.8A for the fan is included in the 59.5A? Wouldn't 59.5x208x1.732 = 21.436kVA be more accurate?

 

[jrohe]

So why add 830 watts for the condenser fan if the 4.8A for the fan is included in the 59.5A? Wouldn't 59.5x208x1.732 = 21.436kVA be more accurate?

Good call. When initially responsing, I did not realize the 4.8 amp condensing unit FLA and the 830 watt condenser fan power were one in the same. You would be correct that the more accurate answer would be 59.5 amps x 208 volts x sqrt(3) = 21,436 VA (7,146 VA per phase). Thanks for catching that.