Filter
Top Products
76 RT-PRC031-EN
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 240-6, select the next lower
standard fuse rating.
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 240-6, select the next higher
standard fuse rating.
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 240-6, select the next lower
standard fuse rating.
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 240-6, select the next higher
standard fuse rating.
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.
Electrical Data