NEC EXPRESS5800 N8800-099F - Manual (Page 60)

4-8 Windows Setup
(2) Execute the operation to be taken when AC power supply is turned off. 

<When the AC power is off (The power cord is not plugged into the outlet)>
Connect the power cords to NEC Express5800/ft series in the following order:
(1) Connect the power cord to the AC inlet (PSU0)
(2) Connect the power cord to the AC inlet (PSU1)
(3) Make sure that the FAULT LED of each module is turned off.
Preparation is now completed.