Installation
24
RT-SVX33E-EN
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%. Measure
and record the voltage between phases 1, 2, and 3 and
calculate the amount of imbalance as follows:
% Voltage Imbalance =
where Average Voltage (AV);
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% imbalance in this example exceeds the
maximum allowable imbalance of 2.0%. This much
imbalance between phases can equal as much as a 20%
current imbalance with a resulting increase in motor
winding temperatures that will decrease motor life. If the
voltage imbalance is over 2%, 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:
•
Turn the field supplied disconnect switch that provides
power to the main power terminal block or to the
“Line” side of the optional factory mounted disconnect
switch to the “Off” position.
•
Connect the phase sequence indicator leads to the
terminal block or to the “Line” side of the optional
factory mounted disconnect switch as follows;
•
Black (phase A) to L1
•
Red (phase B) to L2
•
Yellow (phase C) to L3
•
Close the field supplied main power disconnect switch
or circuit protector switch that provides the supply
power to the unit.
•
Observe the ABC and CBA phase indicator lights on the
face of the sequencer. The ABC indicator light will glow
if the phase is ABC. If the CBA indicator light glows,
open the disconnect switch or circuit protection switch
and reverse any two power wires.
•
Restore the main electrical power and recheck the
phasing. If the phasing is correct, open the disconnect
switch or circuit protection switch and remove the
phase sequence indicator.
Table 6.
Temperature vs. resistance
Temperature
Nominal Resistance
Degrees F°
Degrees C°
-20°
-28.9°
170.1 K - Ohms
-15°
-26.1°
143.5 K - Ohms
-10°
-23.3°
121.4 K - Ohms
-5°
-20.6°
103.0 K - Ohms
0°
-17.8°
87.56 K - Ohms
5°
-15.0°
74.65 K - Ohms
10°
-12.2°
63.80 K - Ohms
15°
-9.4°
54.66 K - Ohms
20°
-6.7°
46.94 K - Ohms
25°
-3.8°
40.40 K - Ohms
30°
-1.1°
34.85 K - Ohms
35°
1.7°
30.18 K - Ohms
40°
4.4°
26.22 K - Ohms
45°
7.2°
22.85 K - Ohms
50°
10.0°
19.96 K - Ohms
55°
12.8°
17.47 K - Ohms
60°
15.6°
15.33 K - Ohms
65°
18.3°
13.49 K - Ohms
70°
21.1°
11.89 K - Ohms
75°
23.9°
10.50 K - Ohms
80°
26.7°
9.297 K - Ohms
85°
29.4°
8.247 K - Ohms
90°
32.2°
7.330 K - Ohms
95°
35.0°
6.528 K - Ohms
100°
37.8°
5.824 K - Ohms
100 AV VD
–
AV
-----------------------
AV
Volt1 Volt2 Volt3
+
+
3
-----------------------------------------------------------------
=
221 230 227
+
+
3
-----------------------------------------------
2.2percent
=
100 226 221
–
226
----------------------------
2.2percent
=
