I've encountered similar applications in commercial kitchens (actually school kitchens) where we needed to get network cables to the electric ovens and fryers, plus the POS terminals when the GC forgot to put pipe in the slab.
We screwed a 3/4" plumbing flange to the floor,
SEE PICTURE HERE, added a 12" X 3/4" galvanized threaded nipple, then threaded a 3/4" X 3-hole FS (weatherproof) outlet box onto it. Of course, you can use any length of pipe from the floor flange to the bottom of the box.
From there, we would thread a full 10' length of 3/4" rigid conduit into this box and, if more height was needed (we're at almost 12 feet in length at this point), another portion of conduit was added. With everything being assembled wrench-tight, it's pretty solid, even with 20 feet of pipe.
In our installations, the box was fitted with the appropriate devices and we placed weatherproof covers to protect from the usual cleaning overspray.
Weatherproof outlet boxes are generally made with cheap aluminum alloy, however you can get type FS boxes made of galvanized cast iron (
LIKE THIS ) through an electrical supplier. They are solid as a rock if you have a harsh environment. If you're going more than 10' above the box, I would recommend that you spend the money on these instead of regular aluminum alloy ones.
Our final attachments above the ceiling were done using traditional fastening methods, such as threaded rod, Minerallac conduit clamps and Unistrut/Kindorf hardware to attach to the building structure.
