Rheem 874 Owner's Manual And Installation Instructions page 63

If it is necessary to have an exposed wiring installation, follow this procedure omitting Steps 24 and 27, and
make an opening in the thin section in the underside of the controller to accommodate the cable (as shown
in the diagram), prior to Step 29.
controller
suitable wall
anchors
opening
projections
terminal
screws
screws
base plate
controller
cable
screw
Kitchen Controller (Standard and Deluxe) Installation
Exposed Cable
63