NEC N8100-1220F User Manual page 389

4.
If you are not going to install a replacement power supply unit, you must install a blank
cover you removed in step 2 of installation procedure to vacant slot.
IMPORTANT:
blank cover in the vacant slot of the power supply bay.
5.
Install the new power supply unit taking steps 3 to 6 of "Installation", and confirm that the
power supply unit is installed normally.
NOTE:
If one of the three or four power supply units of the server is
replaced while the power is on, the POWER lamp of the new power
supply unit goes on. (If it is replaced while the power is off, the lamp
goes on after the power is turned on.)
To maintain the cooling effect in the server, install the
Upgrading Your Server 9-15