heat pumps

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normbac

Senior Member
when calculating feeder for six 3 phase 12000 watt roof top heat pump/ac units is the feeder based on the total load of all units combined reading 220 & 430 I see that I must calculate at 125 percent and rate the branch circuit according to load but I am unsure how the feeder is calculated. I am installing a separate 3phase panel to feed all 6 units. All input appreciated TIA
 
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4SPARKS

Member
Location
New Jersey
From 2008 NEC
220.16 (A) Motor-Operated and Combination Loads. Where a
circuit supplies only motor-operated loads, Article 430 shall
apply. Where a circuit supplies only air-conditioning equipment,
refrigerating equipment, or both, Article 440 shall
apply. For circuits supplying loads consisting of motor operated
utilization equipment that is fastened in place and
has a motor larger than 1⁄8 hp in combination with other loads,
the total calculated load shall be based on 125 percent of the
largest motor load plus the sum of the other loads.
Also check
220.82 (C)
220.83 (A)
for dwelling units not sure if this helps
 
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benaround

Senior Member
Location
Arizona
normbac said:
when calculating feeder for six 3 phase 12000 watt roof top heat pump/ac units is the feeder based on the total load of all units combined reading 220 & 430 I see that I must calculate at 125 percent and rate the branch circuit according to load but I am unsure how the feeder is calculated. I am installing a separate 3phase panel to feed all 6 units. All input appreciated TIA
Click to expand...

Norm, Think of it this way, if it was -20 deg. F. for 2 solid weeks, how much ampacity

would the six units require.
 
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