RT-SVX073A-EN
53
Set 2: Rooftop units with Electric Heat
To arrive at the correct MCA and MOP values for these
units, two sets of calculations must be performed. First
calculate the MCA and MOP values as if the unit was in
cooling mode (use the equations given in Set 1). Then
calculate the MCA and MOP values as if the unit were in
heating mode as follows. (Keep in mind when determining
LOADS that the compressors don't run while the unit is in
heating mode).
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.
Notes:
• 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.
• On 90 to 150 ton rooftops, the selected MOP
value is stamped in the MOP field on the unit
nameplate.
Service Sizing Data
Table 21. Electrical service sizing data
Fixed Capacity Compressors
Nom Tons
Compressor Nominal Voltage
Size
No per Unit
460 V 575 V 380 V
RLA (ea.) LRA (ea.) RLA (ea.) LRA (ea.) RLA (ea.) LRA (ea.)
90 250 4 38.1 215 30.4 175 38.4 215
105 184 6 28.9 160 23.1 135 29.1 160
120
184 4 28.9 160 23.1 135 29.1 160
250 2 38.1 215 30.4 175 38.4 215
130 240 6 36 215 28.8 175 36.3 215
150 250 6 38.1 215 30.4 175 38.4 215
Table 22. Electrical service sizing data
Nom Tons
Compressor Nominal Voltage
Size
No per Unit
460 V 575 V 380 V
RLA (ea.) LRA (ea.) RLA (ea.) LRA (ea.) RLA (ea.) LRA (ea.)
90
170 1 44.6 N/A 35.7 N/A 54 N/A
169 4 26.2 160 20.9 135 26.4 160
105
170 1 44.6 N/A 35.7 N/A 54 N/A
169 3 26.2 160 20.9 135 26.4 160
227 1 36.1 215 28.9 175 36.4 215
120
170 1 44.6 N/A 35.7 N/A 54 N/A
169 2 26.2 160 20.9 135 26.4 160
227 1 36.1 160 28.9 175 36.4 215
285 1 47.5 260 38 210 48 260
130
170 1 44.6 N/A 35.7 N/A 54 N/A
227 3 36.1 215 28.9 175 36.4 215
346 1 57.1 235 45.6 187 57.6 235
Installation
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