Emerson Liebert NX 480V - Manual (Page 82)

Operating Instructions
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9.3 Maintenance Bypass Procedure and Powering Down the UPS
Follow the procedure below to transfer the load from the inverter output to the Maintenance Bypass
line of the UPS.
This procedure assumes that the UPS is operating normally.
1. Press the INVERTER OFF button on the operator control panel for longer than 2 seconds.
The Inverter indicator will turn off and the status indicator will turn amber and an audible alarm
will sound. The load will transfer to static bypass and the inverter will shut off.
2. Close maintenance breaker CB3.
The Maintenance Bypass supply is now in parallel with the UPS Static Switch supply.
3. Open output breaker CB5. This ends the bypass procedure. The load is now powered directly from
the Maintenance Bypass supply.
4. Press the EPO (Emergency Power Off) button at the UPS front panel of this UPS module only.
This will disable further Rectifier, Inverter, Static Switch and Battery operation. This will not
affect the manual maintenance bypass power switch. If a Liebert NX battery cabinet is connected,
the battery circuit breaker will shunt trip open.
5. Open the rectifier switch CB1 and bypass breaker CB2.
All operator indicators and messages will turn off as the utility-driven internal power supplies
decay. The unit will power down, but the load will continue to be supplied by the manual Mainte-
nance bypass.
6. To return unit to normal operation, follow the steps in 9.2.1 - Startup Procedure.
!
CAUTION
Before performing this operation, read the messages on the LCD to be sure that bypass supply
is regular and the inverter is synchronous with it. If those conditions are not present, there is
a risk of a short interruption in powering the load.
NOTE
Pressing the Alarm Silence Switch cancels the audible alarm, but leaves the warning message
displayed until the relevant condition is rectified.
!
WARNING
Wait 5 minutes for the internal DC busbar capacitors to discharge before attempting
to remove the internal protective barriers.
!
WARNING
Even with the UPS in maintenance bypass and “Off,” portions of the unit are still energized.
Service is to be performed by qualified personnel only.
!
CAUTION
The load equipment is not protected from normal supply aberrations when operating in
maintenance bypass mode.