Operation
25 Liebert
®
NX
™
2.6.2 Automatic Transfers to Bypass (Overload Condition)
The UPS system will initiate an automatic load transfer to the bypass line if an overload condition
exceeds the current-versus-time curve of overload capacity or if specified UPS system faults occur.
The Overload Transfer and Output Undervoltage alarm messages will initiate an automatic transfer
to bypass. Other UPS system faults will initiate an automatic transfer to bypass followed
immediately by the shutdown and isolation of the UPS system. Refer to 2.6.3 - Automatic Transfers
to Bypass, UPS System Faults.
2.6.3 Automatic Transfers to Bypass, UPS System Faults
For specified UPS system faults, the control logic will initiate an automatic transfer to bypass
followed immediately by a shutdown and isolation of the UPS system. The DC source (MBD) and
input circuit breakers are open. The bypass static switch will be closed if the bypass line is available.
The following UPS system faults will initiate an automatic transfer to bypass:
• DC Overvoltage Shutdown
• Inverter Fault
• Low-Battery Shutdown
• Output Overvoltage and Undervoltage
• Overload Shutdown
• Equipment Overtemperature
• Rectifier Fuse Blown
Some installations may include a Remote Emergency Power Off mode that can be initiated
automatically by a contact closure in the critical load equipment. Refer to 2.4.4 - Remote
Emergency Power Off.
NOTE
A load transfer to the bypass line will be completed whenever an automatic transfer to bypass
is initiated. If the OK to Transfer condition is present, the load transfer will be uninterrupted.
If the Static Switch Unable alarm message is present for any reason, the automatic transfer
will be interrupted for 40 to 120 milliseconds. Because of the reliability of the UPS components,
an interrupted load transfer is a very unlikely occurrence.
NOTE
The bypass line is usually not available during Low Battery Shutdown.
NOTE
A load transfer to the bypass line will be completed whenever an automatic transfer to bypass
is initiated and the bypass line is available. If the OK to Transfer condition is present, the load
transfer will be uninterrupted. If the Static Switch Unable alarm message is present for any
reason, the automatic transfer will be interrupted for 40 to 120 milliseconds. Because of the
reliability of the UPS components, an interrupted load transfer is a very unlikely occurrence.
