38 RT-SVX23D-EN
Pre-Start
• Verify that the correct size and number of filters are in place.
• Inspect the interior of the unit for tools and debris and install all panels in preparation for
starting the unit.
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:
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
% Voltage Imbalance = 100 X AV - VD where;
AV
AV (Average Voltage) Volt 1 + Volt 2 + Volt 3
3
221 + 230 + 227
= 226 Avg.
3
100 X 226 - 221
= 2.2%
226
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