10
Example
:
AB = 451V
BC = 460V
AC = 453V
2. Determine the average voltage in the power supply.
3. Determine the maximum deviation:
4. Determine percent of
voltage imbalance by
using the results from
steps 2 & 3 in the
following equation.
max voltage deviation
from average voltage
= 100 x
average voltage
% Voltage Imbalance
6
454
100 x
= 1.32%
Example:
1. M e a s u r e t h e l i n e
voltages of your 3-phase
power supply where it
enters the building and
at a location that will
only be dedicated to the
unit installation (at the
units circuit protection
or disconnect).
Unbalanced 3-Phase Supply Voltage
Voltage unbalance occurs when the voltages of all phases
of a 3-phase power supply are no longer equal. This
unbalance reduces motor effi ciency and performance.
Some underlying causes of voltage unbalance may include:
Lack of symmetry in transmission lines, large single-phase
loads, and unbalanced or overloaded transformers. A
motor should never be operated when a phase imbalance
in supply is greater than 2%.
Perform the following steps to determine the percentage
of voltage imbalance:
In this example, the measured line voltages were
451, 460, and 453. The average would be 454 volts
(451 + 460 + 453 = 1,364 / 3 = 454).
The amount of phase imbalance (1.32%) is satisfactory
since the amount is lower than the maximum allowable
2%. Please contact your local electric utility company if
your voltage imbalance is more than 2%.
Example:
From the values given in step 1, the BC voltage
(460V) is the greatest difference in value from
the average:
460 - 454 = 6
454 - 451 = 3
454 - 453 = 1
Highest Value
Thermostat Connections
• Thermostat connections should be made in accordance
with the instructions supplied with the thermostat and
the indoor equipment.
• Single stage or two-stage thermostats can be used
with this equipment depending on optional accessories
(i.e. economizer) installed with the unit. Select a
thermostat that operates in conjunction with the installed
accessories. A typical commercial installation with a
heat pump thermostat and air handler (with & without
an economizer) is shown in Figure 7 (page 17).
• The outdoor unit is designed to operate from a 24 VAC
Class II control circuit. The control circuit wiring must
comply with the current provisions of the NEC (ANSI/
NFPA 70) and with applicable local codes having
jurisdiction.
• The low voltage wires must be properly connected to
the units low voltage terminal block. Recommended
wire gauge and wire lengths for typical thermostat
connections are listed in Table 2.
• The
thermostat should be mounted about 5 feet
above the fl oor on an inside wall. DO NOT install the
thermostat on an outside wall or any other location
where its operation may be adversely affected by radiant
heat from fi replaces, sunlight, or lighting fi xtures, and
convective heat from warm air registers or electrical
appliances. Refer to the thermostat manufacturer’s
instruction sheet for detailed mounting and installation
information.
Table 2. Thermostat Wire Gauge
Thermostat
Wire Gauge
Recommended T-Stat Wire
Length (Unit to T-Stat)
2-Wire
(Heating)
5-Wire
(Heating/Cooling)
24
55
25
22
90
45
20
140
70
18
225
110
Defrost Cycle Timer
The defrost cycle timer controls the time interval of the hot
gas defrost after the defrost sensor closes. It is located
in the lower left corner of the defrost control board on the
low voltage side of the control box. Three interval settings
are available: 30 minutes, 60 minutes, and 90 minutes.
Time setting selection is dependent on the climate where
the unit is being installed.
• Example 1: Dry climate of Southern Arizona - A 90
minute setting is recommended.
• Example 2: Moist climate of Seattle, Washington - A
30 minute setting is recommended.
