IBM System p Series Cabling Manual page 56

Connecting the power cords
__ If your server is equipped with a retention ring, route the power cord through the ring before you plug it
into the back of the server. See the following figure as an example:
__ If your server is equipped with a retention bracket, route the power cord under the bracket before you
plug it into the back of the server. See the following figure as an example:
__ Plug the power cords into the system, display, and attached devices.
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System i and System p: Cabling your server