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Introduction to Variable-Frequency Drives
Getting Started
1–14
Inverter Output to the Motor
The AC motor must be connected only to the inverter’s
output terminals. The output terminals are uniquely
labeled (to differentiate them from the input terminals)
with the designations U/T1, V/T2, and W/T3. This
corresponds to typical motor lead connection designa-
tions T1, T2, and T3. It is often not necessary to connect
a particular inverter output to a particular motor lead for
a new application. The consequence of swapping any
two of the three connections is the reversal of the motor
direction. In applications where reversed rotation could
cause equipment damage or personnel injury, be sure to verify direction of rotation
before attempting full-speed operation. For safety to personnel, you must connect the
motor chassis ground to the ground connection at the bottom of the inverter housing.
Notice the three connections to the motor do not include one marked “Neutral” or
“Return.” The motor represents a balanced “Y” impedance to the inverter, so there is no
need for a separate return. In other words, each of the three “Hot” connections serves
also as a return for the other connections, because of their phase relationship.
The Hitachi inverter is a rugged and reliable device. The intention is for the inverter to
assume the role of controlling power to the motor during all normal operations. There-
fore, this manual instructs you not to switch off power to the inverter while the motor is
running (unless it is an emergency stop). Also, do not install or use disconnect switches
in the wiring from the inverter to the motor (except thermal disconnect). Of course,
safety-related devices such as fuses must be in the design to break power during a
malfunction, as required by NEC and local codes.
3-Phase AC Motor
U/T1
V/T2
W/T3
Earth
GND