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RTAC-SVX01F-EN 141
Pre-Start Checkout
CAUTION
Equipment Damage!
Provide adequate voltage to the unit. Failure to do so can cause control
components to malfunction and shorten the life of relay contact,
compressor motors and contactors.
Unit Voltage Imbalance
Excessive voltage imbalance between the phases of three-phase system can cause
motors to overheat and eventually fail. The maximum allowable imbalance is 3%. Volt
-
age imbalance is determined using the following calculations:
% Imbalance = [(Vx - V ave) x 100]/Vave
V ave = (V1 + V2 + V3)/3
Vx = phase with the greatest difference from V ave (without regard to the sign)
For example, if the three measured voltages are 221, 230, and 227 volts, the average
would be:
(221+230+227)/3 = 226
The percentage of the imbalance is then:
[100(221-226)]/226 = 2.2%
This exceeds the maximum allowable (2%) by 0.2 percent.
Unit Voltage Phasing
CAUTION
Compressor Damage!
It is imperative that L1, L2, L3 in the starter be connected in the A-B-C
phase sequence to prevent equipment damage due to reverse rotation.
It is important that proper rotation of the compressors be established before the unit
is started. Proper motor rotation requires confirmation of the electrical phase
sequence of the power supply. The motor is internally connected for clockwise rota
-
tion with the incoming power supply phased A, B, C.
Basically, voltages generated in each phase of a polyphase alternator or circuit are
called phase voltages. In a three-phase circuit, three sine wave voltages are gener
-
ated, differing in phase by 120 electrical degrees. The order in which the three volt-
ages of a three-phase system succeed one another is called phase sequence or
phase rotation. This is determined by the direction of rotation of the alternator. When
rotation is clockwise, phase sequence is usually called "ABC," when counterclock
-
wise, "CBA.”
This direction may be reversed outside the alternator by interchanging any two of the
line wires. It is this possible interchange of wiring that makes a phase sequence indi
-
cator necessary if the operator is to quickly determine the phase rotation of the
motor.
Proper compressor motor electrical phasing can be quickly determined and corrected
before starting the unit. Use a quality instrument, such as the Associated Research
Model 45 Phase Sequence Indicator, and follow this procedure.
1. Press the STOP key on the CH530.
2. Open the electrical disconnect or circuit protection switch that provides line
power to the line power terminal block(s) in the starter panel (or to the unit-
mounted disconnect).