Trane RTAA-100, Installation & Maintenance Manual

Page: 106 / 178

106 RTAA-SVX01A-EN
Pre-Start Checkout
Unit Voltage Phasing
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 rotation 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 generated, differing in phase by 120 electrical degrees. The order in which
the three voltages 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 counterclockwise, “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 indicator 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 Clear Language Display.
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).
3. Connect the phase sequence indicator leads to the line power terminal
block, as follows:
Phase Sea. Lead Terminal
Black (Phase A) ..................... L1
Red (Phase B) ....................... L2
Yellow (Phase C) .................... L3
4. Turn power on by closing the unit supply power fused disconnect switch.
5. Read the phase sequence on the indicator. The “ABC” LED on the face of
the phase indicator will glow if phase is “ABC”.
WARNING
Live Electrical Components!
During installation, testing, servicing and troubleshooting of this
product, it may be necessary to work with live electrical
components. Have a qualified licensed electrician or other
individual who has been properly trained in handling live
electrical components perform these tasks. Failure to follow all
electrical safety precautions when exposed to live electrical
components could result in death or serious injury.
6. If the “CBA” indicator glows instead, open the unit main power discon-
nect and switch two line leads on the line power terminal block(s) (or the
unit mounted disconnect). Reclose the main power disconnect and
recheck the phasing.