Electrical Wire Sizing And Protection; Device Equations; Calculation #1 - Tc*, Yc* - 27.5 To; Ton Units - Trane Voyager Commercial Installation, Operation And Maintenance Manual

Table 13. Electrical service sizing data – electric heat
module (electric heat units only)—50Hz
Models: TE(D,H,F,R) 275 through 500 Electric Heat
Nominal Nominal
Unit Size Unit
23/
(Tons) Voltage
380 34.5
23-29
415 37.6
380
33, 42
415
Note: All FLA in this table are based on heater operating at 380
or 415 volts as shown above.
Table 14. Electrical service sizing data — crankcase
heaters (heating mode only) — 50Hz
Nominal Unit
Size (Tons)
23 - 29
33 - 42
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 (Maximum 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
• 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 1 Amp
• 40 - 50 Ton Units, Add 2 Amps
RT-SVX34R-EN
FLA
KW Heater (380/415V)
34/ 45/ 56/
27 40 54 67
51.1 68.9 85.5
55.6 – –
– 51.1 68.9 85.5
– 55.6 75.1 93.2
FLA Add
Unit Voltage
380 415
1 1
1 1
– 460/575 VOLT
• 27.5 - 35 Tons Units, Add 1 Amp
• 40 - 50 Ton Units, Add 1 Amp
Calculation #1 - TC*, YC* - 27.5 to 50 Ton

Units

68/
81 • MCA = (1.25 x Load 1) + Load 2 + Load 4
• MOP = (2.25 x Load 1) + Load 2 + Load 4 (See Note
–
1)
–
N N o o t t e e : : Select an over current protection device
103-
equal to the MOP value. If the calculated
.4
MOP value does not equal a standard size
112-
protection device listed in NEC 240-6, select
.7
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.
• RDE = (1.5 x Load 1) + Load 2 + Load 4 (See Note 2)
N N o o t t e e : : 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.

Calculation #2 - TE* - 27.5 to 50 Ton

Units
N N o o t t e e : : The following applies to single source power
units (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:
• Calculate the MCA, MOP and/or RDE values using
the above equation as if the unit is operating in the
cooling mode.
• Calculate the MCA, MOP and/or RDE values as if the
unit is operating in the heating mode, as follows:
N N o o t t e e : : 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
N N o o t t e e : : The MCA value stamped on the nameplate is
the largest of the two calculated values.
I I n n s s t t a a l l l l a a t t i i o o n n E E l l e e c c t t r r i i c c a a l l
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