Junction boxes on roof roof decking

[Thane]

I agree and IMO this is a terrible code requirement. For decades EMT and metal boxes were installed on the decking without much of a problem. Yes it's possible that sometime in the future a roofing fastener may penetrate the EMT but odds are slim. I would put it up there with the odds of a homeowner using a 3" nail to hang a picture and hitting an NM cable. :slaphead:

I've recently dealt with 8 screws in three conduit runs. They ran in the corrugation above the joists for rtus at Staples and Sears. The corrugation space was filled so the conduits couldn't move. I think it's a good rule to keep them away from the deck. In fact the rule was in place when the contractor did those jobs. Because of bad selective load coordination at staples it caused the main to trip!

 

[jusme123]

I understand that you cannot fasten conduit directly on the underside of corrugated roof decking. What does this mean in regards to mounting junction boxes? Do they have to be mounted on strut? Everywhere I go I see boxes mounted directly onto the corrugated deck.
Does the new code prohibit this method? It seems very labor intensive to have to mount every box on a piece of unistrut.

I know this is an old post, but what was the conduit used for (lights, outlets, fire alarm)?