Trane SRUB, Installation Operation & Maintenance

Page: 20 / 27

20
SRUB-IOM001-EN
Electrical Information
Unit Voltage
Electrical power to the unit must meet stringent requirements
for the unit to operate properly. Total voltage supply and voltage
imbalance between phases should be within the following
tolerances.
Voltage Supply
Measure each leg of supply voltage at all line voltage
disconnect switches. Readings must fall within the voltage
utilization range shown on the unit nameplate. If voltage on
any leg does not fall within tolerance, notify the power
company to correct this situation before operating the unit.
Inadequate voltage to the unit will cause control components
to malfunction and shorten the life of electrical components
and compressor motors.
Voltage Imbalance
Excessive voltage imbalance between phases in a three-phase
system will cause motors to overheat and eventually fail.
Maximum allowable imbalance is 2 percent. Voltage imbalance
is defined as follows:
% Voltage Imbalance =
100 x [V
A
- V
D
]
V
A
Where V
A
= = (Avg. Voltage)
V
1
,V
2
,V
3
= Line Voltage
V
D
= Line Voltage that deviates farthest from V
A
.
Example :
If the three voltages measured at the line voltage fused
disconnect are 370 volts, 381 volts and 384 volts, the average
(V
A
) would be:
V
1
+V
2
+V
3
3
= 378.3 volts.
V
D
= 370
The percentage of imbalance is then:
370 + 381 +384
3
= 2.2%
100 x [378.3 - 370]
378.3
The 2.2 percent imbalance that exists in the example above
exceeds maximum allowable imbalance by 0.2 percent. This
much imbalance between phases can equal as much as 20
percent current imbalance with a resulting increase in winding
temperature that will decrease compressor motor life.