22
Figure 9
Electrical Wire Sizing and Protection Device Equations
To correctly size the main power wiring based on MCA (Minimum Circuit Ampacity), use the appropriate equation listed below.
Read the definitions that follow and then use
Calculation
#1
for determining MCA (Minimum Circuit Ampacity), MOP (Maxi-
mum Over current Protection), and RDE (Recommended Dual Element fuse size) for TC (Cooling Only) units and YC (Cooling
with Gas Heat) units. Use
Calculation
#2
for TE (Cooling with Electric Heat) units.
Load Definitions:
LOAD 1
= CURRENT OF THE LARGEST MOTOR ( Compressor or Fan Motor)
LOAD
2
= SUM OF THE CURRENTS OF ALL REMAINING MOTORS
LOAD
3
= FLA (Full Load Amps) OF THE ELECTRIC HEATER (See Table 6)
LOAD
4
= ANY OTHER LOAD RATED AT 1 AMP OR MORE
CRANKCASE HEATERS FOR HEATING MODE ONLY - 208/230 VOLT
- 27.5 - 35 Ton Units, Add 2 Amps
- 40 - 50 Ton Units, Add 3 Amps
460/575 VOLT
- 27.5 - 35 Tons Units, Add 1 Amp
- 40 - 50 Ton Units, Add 2 Amps
Calculation #1 - TC*, YC*-27.5 through 50 Ton Units
MCA
= (1.25 x Load 1) + Load 2 + Load 4
MOP
= (2.25 x Load 1) + Load 2 + Load 4
(See
Note
1)
RDE
= (1.5 x Load 1) + Load 2 + Load 4
(See
Note
2)
Calculation # 2 - TE*-27.5 through 50 Ton Units
A. Single Source Power (all voltages)
To calculate the correct MCA (Minimum Circuit Ampacity), MOP (Maximum Over current Protection), and RDE (Recommended
Dual Element fuse size), two (2) sets of calculations must be performed;
1. Calculate the MCA, MOP and/or RDE values using the above equation as if the unit is operating in the cooling mode.
2. Calculate the MCA, MOP and/or RDE values as if the unit is operating in the heating mode, as follows:
Note: When determining loads, the compressors and condenser fan motors do not operate during the heating
cycle.
Units
with
less
than
50
KW
Heaters
MCA
= 1.25 x (Load 1 + Load 2 + Load 4) + (1.25 x Load 3)
Units
with
50
KW
or
Larger
Heaters
MCA
= 1.25 x (Load 1 + Load 2 + Load 4) + Load 3
The MCA value stamped on the nameplate is the largest of the two calculated values.
MOP
= (2.25 x Load 1) + Load 2 + Load 3 + Load 4
(See
Note
1)
The MOP value stamped on the nameplate is the largest of the two calculated values.
RDE
= (1.5 x Load 1) + Load 2 + Load 3 + Load 4
(See
Note
2)
Notes:
1. Select an over current protection device equal to the MOP value. If the calculated MOP value does not equal a
standard size protection device listed in NEC 240-6, select the next lower over current protection device. If the
calculated MOP value is less than the MCA value, select the lowest over current protection device which is equal
to or larger than the MCA, providing the selected over current device does not exceed 800 amps.
2. Select a Dual Element Fuse equal to the RDE value. If the calculated RDE value does not equal a standard dual
element fuse size listed in NEC 240-6, select the next higher fuse size. If the calculated RDE value is greater than
the MOP value, select a Dual Element fuse equal to the calculated MOP (Maximum Over current Protection) value
Disconnect Switch Sizing (DSS)
Calculation A. - YC*, TC*, and TE* Units:
DSS = 1.15 X (LOAD1 + LOAD2 + LOAD4)
For TE* units, use calculations A and B.
Calculation B. - TE* Units:
DSS = 1.15 X (LOAD3 + Supply Fan FLA + Exhaust Fan FLA).
Use the larger value of calculations A or B to size the electrical disconnect switch.
Summary of Contents for Voyager RT-SVX17C-EN
Page 8: ...8 Figure 1 Unit Dimensions for TC_ TE_ and YC_330 360 and 420 MBH Units Low Heat ...
Page 9: ...9 Figure 1 continued Unit Dimensions for YC_330 360 and 420 MBH Units High Heat ...
Page 10: ...10 Figure 1 continued Unit Dimensions for TC_ TE_ and YC_480 and 600 MBH Units Low High Heat ...
Page 24: ...24 Figure 10 Typical FieldWiring Requirements for CV Control Options ...
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