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WARNING
Hazardous
voltage
Section 6
Power Supply
NOTE
Installation and maintenance MUST be performed by properly trained and qualified personnel. Always follow
the National Electrical Code (NEC) or Canadian Electric Code (CEC), as well as all state, local and provincial
codes when wiring the system.
The type of transformer and the connection configuration feeding a drive plays an important role in its
performance and safety. The following is a brief description of some of the more common configurations and a
discussion of their virtues and shortcomings. Always ask what type of power system the site has before sizing the
drive.
Delta/Wye with grounded Wye neutral
This configuration is one of if not the most common. It provides rebalancing of unbalanced voltage with a 30
degree phase shift. Depending on the output connections from the drive to motor, the grounded neutral may be
a path for common mode current caused by the drive output.
Delta/Delta with grounded leg
Another common configuration providing voltage rebalancing with no phase shift between input and output.
Again, depending on the output connections from the drive to motor, the grounded neutral may be a path for
common mode current caused by the drive output.
In this case the line to ground voltage on the phases that are not grounded will be equal to the phase to phase
voltage. This voltage can exceed the voltage ratings of the EMC filter and input MOV protection devices. This can
cause catastrophic controller failure if the line to ground EMC filter and input MOV protection devices are not
disconnected. Refer to Disconnecting EMC Filter and MOVs for details on line to ground voltage limitations and
disconnecting these devices.
WARNING
If the secondary of the transformer is a delta with a grounded leg (corner grounded delta), the
line to ground EMC filter components and line to ground MOV protection must be disconnected
or damage to the controller can result.
POWER SUPPLY AND WIRING
