Dell S4048T-ON Guide De Mise En Route page 21

AC power supplies with two air-flow directions (I/O to Utility and Utility to
I/O).
1. Remove the PSU from the electrostatic bag.
2. Remove the PSU slot cover from the switch.
3. Use the grab handle to slide the PSU into the switch PSU slot. The PSU
slot is keyed such that the PSU can only be fully inserted in one
orientation.
The PSU slides into the slot smoothly. Do not force the PSU into a slot as
this action may damage the PSU or the chassis.
Figure 11. Install the AC or DC Power Supply Unit
4. Repeat steps 1 through 3 for the second PSU.
WARNING: The PSU side includes two slots, PSU1 and PSU2. Although
the switch can run on one PSU, Dell Networking highly recommends
using two PSUs for full redundancy and additional cooling. To avoid
overheating when the switch is running with only a single PSU, Dell
Networking recommends using PSU1 (on the left when facing the PSU
side) and covering the second PSU slot opening (PSU2) with a blank
plate.
WARNING: ESD damage can occur if components are mishandled.
Always wear an ESD-preventive wrist or heel ground strap when
handling the system and its components.
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