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Installation
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 =
100 X AV - VD
AV (Average Voltage) =
Volt 1 + Volt 2 + Volt 3
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:
221 + 230 + 227
•
•
100 X 226 - 221
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:
34
where;
AV
3
= 226 Avg.
3
VD (reading farthest from average) = 221
The percentage of Imbalance equals:
= 2.2%
226
RT-SVX25C-EN
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