Trane IntelliPak SAHL Series Installation, Operation And Maintenance Manual page 107

Voltage Imbalance
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 =
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:
221 + 230 + 227
VD (reading farthest from average) = 221
The percentage of Imbalance equals:
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.
RT-SVX36G-EN
100 X AV - VD where;
AV
Volt 1 + Volt 2 + Volt 3
3
= 226 Avg.
3
= 2.2%
226
Unit Start Up
107