Installation
RT-SVX50F-EN
19
1. Use copper conductors unless otherwise specified.
2. Ensure that the AC control wiring between the controls
and the unit’s termination point does not exceed three
(3) ohms/conductor for the length of the run.
Note:
Resistance in excess of 3 ohms per conductor
could cause component failure due to insufficient
AC voltage supply.
3. Be sure to check all loads and conductors for grounds,
shorts, and mis-wiring.
4. Do not run the AC low voltage wiring in the same
conduit with the high voltage power wiring.
5. Route low voltage wiring per illustrations on
the next
page.
Voltage Imbalance
Three phase electrical power to the unit must meet
stringent requirements for the unit to operate properly.
Measure each leg (phase-to-phase) of the power supply.
Each reading must fall within the utilization range stamped
on the unit nameplate. If any of the readings do not fall
within the proper tolerances, notify the power company to
correct this situation before operating the unit.
Excessive three phase voltage imbalance between phases
will cause motors to overheat and eventually fail.
The maximum allowable voltage imbalance is 2 percent.
Measure and record the voltage between phases 1, 2, and
3 and calculate the amount of imbalance as follows:
% Voltage Imbalance =
AV (Average Voltage) =
•
V1, V2, V3 = Line Voltage Readings
•
VD = Line Voltage reading that deviates the farthest
from the average voltage.
Example: If the voltage readings of the supply power
measured 221, 230, and 227, the average volts would be:
•
VD (reading farthest from average) = 221
•
The percentage of Imbalance equals:
The 2.2 percent imbalance in this example exceeds the
maximum allowable imbalance of 2.0 percent. This much
imbalance between phases can equal as much as a
20 percent current imbalance with a resulting increase in
motor winding temperatures that will decrease motor life.
If the voltage imbalance is over 2 percent, notify the proper
agencies to correct the voltage problem before operating
this equipment.
Electrical Phasing (Three Phase Motors)
The compressor motor(s) and the supply fan motor are
internally connected for the proper rotation when the
incoming power supply is phased as A, B, C.
Proper electrical supply phasing can be quickly
determined and corrected before starting the unit by using
an instrument such as an Associated Research Model 45
Phase Sequence Indicator and following the steps below:
Table 2.
Electromechanical thermostat 24V AC
conductors with electromechanical unit
Distance from Unit to Control
Recommended Wire Size
0 - 30 feet
22 gauge
0 - 9.1 m
.33 m2
31 - 50 feet
20 gauge
9.5 - 15.2 m
.50m2
51 - 75 feet
18 gauge
15.5 - 22.9 m
.75 m2
76 - 125 feet
16 gauge
23.1 - 38.1 m
1.3 m2
126 - 200 feet
14 gauge
38.4 - 60.9 m
2.0 m2
Figure 14.
Conventional thermostat field wiring
diagram
100 X AV - VD
where;
AV
Volt 1 + Volt 2 + Volt 3
3
221 + 230 + 227
= 226 Avg.
3
100 X 226 - 221
= 2.2%
226