8.3.2 Maintenance Bypass Procedures
W A RN IN G! If the U PS system is com posed of tw o or m o re parallel connected UPS modules,
and the load capacity exceeds the single UPS module capacity, d o not use the internal
m aintenance bypass switch (Q 3).
This operation will make the load transfer from UPS power supply protection state to direct connection with AC input bypass
state.
CA U T IO N: Pow er supply interruption danger of the load.
Before performing this procedure, you should check the touchscreen information first, and make sure the bypass is normal
and inverter synchronized. Otherwise, it may result in the load power interruption for a while.
1. Manually turn off the inverter of each UPS. The power flow diagram shows INVERTER OFF, and the buzzer
alarms. The load transfers to the static bypass, and the inverter shuts down. At last, all UPSs are transferred to
Bypass mode.
N O T E: P ress th e SILENC E button can silence the alarm , but the alarm m essage of the
TO U C H SC R EEN does not disap pear until the alarm status is cleared.
2. Recommend to close the UPS external total maintenance bypass switches as it is safe. And do not close the
internal maintenance bypass switch Q3 of each UPS.
3. At this moment, the external total maintenance bypass should be connected parallel with each UPS's static
switch.
4. At this moment, the TOUCHSCREEN of each UPS displays ' Maint. Switch Closed only if external maintenance
bypass switch is available and monitored by dry Input contact.
5. Disconnect the output switch Q5 of each UPS in turn, and the maintenance bypass can supply power to the load.
CA U T IO N: Load is not secured on the m aintenance bypass anym ore unless there is Power
generator ru n ning instead of norm al grid u tility
6. Pressing the EPO button of each UPS stops the operation of rectifier, inverter, static switch and battery, but this
action will not affect the maintenance bypass power the load normally.
N O T E: In m aintenance m ode, the load is d irectly fed by the m ains pow er instead of the pure A C
pow er from th e inverter.
7. Disconnect the rectifier input switch Q1, bypass input switch Q2, and BCB if available of each UPS
At the moment, all the internal power supply is off and the TOUCHSCREEN does not display any more.
8 Parallel System and LBS System
145
Vertiv™ Liebert® EXM2 UPS User Manual
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