1. Press the power button of each UPS to shutdown the inverter, till all the UPSs in parallel system transfer to
bypass mode.
2. Close the UPS external total maintenance bypass switches, and do not close the internal maintenance bypass
switch Q3 of each UPS.
3. At this moment, the external total maintenance bypass should be parallely connected with each UPSs bypass.
4. At this moment, the LCD of each UPS displays maint. switch closed.
WARNING! When the UPS is in maintenance mode, the load does not have the mains abnormal protection.
5. Press the remote EPO button of each UPS for 2 seconds (if any) or unplug the EPO terminal of each UPS to stop
the operation of rectifier, inverter, bypass, and battery, but this action will not affect the maintenance bypass
power the load normally.
NOTE: In maintenance mode, the load is directly fed by the mains power instead of the pure AC power from the
inverter.
6. Disconnect the main input switch Q1, bypass input switch Q2, and output switch Q5 of each UPS in turn.
At present, all the internal power supply is off, and the LCD no longer displays.
7. If the UPS is equipped with internal batteries, ensure that they have been isolated from the UPS before carrying
out maintenance work on it. If the UPS is equipped with an external battery, set the corresponding external
battery switch to off.
6.4.5 Isolating one UPS module from parallel system
WARNING! These procedures shall only be carried out by service personnel of Vertiv or under their guidance.
WARNING! Before operation, confirm that the system capacity has redundancy to avoid system shutdown
due to overload.
The following procedures apply when one UPS module must be isolated from the parallel system for repair due to serious
fault:
1. Unplugging the EPO terminal stops the operation of rectifier, inverter, bypass, and battery, but this action will not
affect other UPSs in parallel system to normally power the load.
2. Disconnect the main input switch Q1, bypass input switch Q2, and output switch Q5 of the UPS. At present, all the
internal power supply is off, and the LCD no longer displays.
3. If the UPS is equipped with internal batteries, make ensure that they have been isolated from the UPS before
carrying out maintenance work on it. If the UPS is equipped with an external battery, set the corresponding
external battery switch to off.
WARNING! Post a label at the AC input distribution (generally far away from the UPS) to alert that the UPS
maintenance is being operated.
52 Proprietary and Confidential ©2023 Vertiv Group Corp. 6 Parallel System and LBS System
Vertiv™ Liebert® EXS Installer/User Guide
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