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Operation
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Maintenance Mode
For maintenance or repair, the Liebert NX may be operated in maintenance mode. To place the Lie-
bert NX in maintenance mode, the load must be transferred to bypass and the inverter must be
turned off. When those conditions are met, the CB3 may be turned on and the UPS may be shut down,
permitting disconnecting the batteries for maintenance.
Parallel Redundancy Mode (System Expansion)
For higher capacity, higher reliability or both, the outputs of up to four UPS modules can be pro-
grammed for directly paralleling while a built-in parallel controller in each UPS ensures automatic
load-sharing.
Frequency Converter Mode
The Liebert NX can be programmed into frequency converter mode for either 50Hz or 60Hz stable
output frequency. The input frequency may vary from 57Hz to 66Hz. In this mode, the static bypass
operation is disabled and the battery becomes optional, depending on any requirement to operate in
battery mode (stored energy mode).
If ECO mode is selected, the double-conversion UPS operation is inhibited at most times for the pur-
pose of saving energy. In this mode of operation, not unlike UPS of line-interactive or stand-by tech-
nology, the bypass is the preferred source, and only when the voltage and/or frequency of the bypass
supply is beyond pre-defined and adjustable limits is the critical AC load transferred to the inverter.
This transfer takes place with an interruption of less than 3/4 of an electrical cycle, e.g., less than
15ms (50Hz) or less than 12.5ms (60Hz).
!
CAUTION
The internal maintenance bypass must not be used when the UPS system is in a parallel
system.
!
WARNING
The UPS input and output must be protected with external overcurrent protection devices. In
maintenance mode, the input and output busbars remain energized.