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Originally posted by EV607797:
If you know for sure that plywood is behind the sheetrock, you will be fine with 1/4" toggle bolts. If you drill 5/8" holes for the toggles and don't hit wood, then I'd attach my own piece of plywood to the surface and screw it to the studs.

If this is the case, use fine-thread screws, not the coarse ones to mount the plywood. Some construction adhesive on the back wouldn't be a bad idea and it is cheap insurance.
Yes there's plywood. I saw it myself. Not sure if the AHJ in Quebec require fire rated board though. In Quebec, I've seen every kind of wood board possible used a backboard in telecom/electrical rooms and they never got any complaints from the AHJ. Will pickup some toggle bolts this weekend to do the install.

Thanks