Electrical Data
Electrical Service Sizing
To correctly size electrical service wiring for a unit, find the appropriate calculations listed below. Each type of unit has its own set of calculations for MCA (Minimum Circuit Ampacity), MOP (Maximum Overcurrent Protection), and RDE (Recommended Dual Element fuse size). Read the load definitions that follow and then find the appropriate set of calculations based on unit type.
Note: Set 1 is for cooling only and cooling with gas heat units, and set 2 is for cooling with electric heat units.
Load Definitions: (To determine load values, see the Electrical Service Sizing Data Tables on the following page.)
LOAD1 = CURRENT OF THE LARGEST MOTOR
LOAD2 = SUM OF THE CURRENTS OF ALL REMAINING MOTORS
LOAD3 = CURRENT OF ELECTRIC HEATERS
LOAD4 = ANY OTHER LOAD RATED AT 1 AMP OR MORE
Set 1. Cooling with Gas Heat Air Handling Units
MCA = (1.25 x LOAD1) + LOAD2 + LOAD4
MOP = (2.25 x LOAD1) + LOAD2 + LOAD4
Select a fuse rating equal to the MOP value. If the MOP value does not equal a standard fuse size as listed in NEC
Note: If selected MOP is less than the MCA, then select the lowest standard maximum fuse size which is equal to or larger than the MCA, provided the selected fuse size does not exceed 800 amps.
RDE = (1.5 x LOAD1) + LOAD2 + LOAD4
Select a fuse rating equal to the RDE value. If the RDE value does not
equal a standard fuse size as listed in NEC
Note: If the selected RDE is greater than the selected MOP value, then select the RDE value to equal the MOP value.
Set 2. Cooling with Electric Heat
To arrive at the correct MCA, MOP, and RDE values for these units, two sets of calculations must be performed. First calculate the MCA, MOP, and RDE values as if the unit was in cooling mode (use the equations given in Set 1). Then calculate the MCA, MOP, and RDE values as if the unit were in the heating mode as follows.
MCA = 1.25 x (LOAD1 + LOAD2 + LOAD4) + LOAD3
The nameplate MCA value will be the larger of the cooling mode MCA value or the heating mode MCA value calculated above.
MOP = (2.25 x LOAD1) + LOAD2 + LOAD3 + LOAD4
The selection MOP value will be the larger of the cooling mode MOP value or the heating mode MOP value calculated above.
Select a fuse rating equal to the MOP value. If the MOP value does not equal a standard fuse size as listed in NEC
Note: If selected MOP is less than the MCA, then select the lowest standard maximum fuse size which is equal to or larger than the MCA, provided the selected fuse size does not exceed 800 amps.
RDE = (1.5 x LOAD1) + LOAD2 + LOAD3 + LOAD4
The selection RDE value will be the larger of the cooling mode RDE value or the heating mode RDE value calculated above.
Select a fuse rating equal to the RDE value. If the RDE value does not equal a standard fuse size as listed in
NEC
Note: If the selected RDE is greater than the selected MOP value, then select the RDE value to equal the MOP value.
GENERAL NOTE
Note: The selected MOP value is stamped in the MOP field on the nameplate.
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