When installing a 2x4 troffer in a fire rated dropped ceiling, is anything required other than an FR rating on the fixture? I'm specifically interest in special covers that go over the fixture, such as the ones made by TENMAT.
I rarely get into work that requires fire ratings. I don't recall ever seeing anything special being done for a lay in troffer in the fire rated ceilings I've looked in.
Few things are harder to put up with than the annoyance of a good example.
Ceilings -and walls, for that matter- are rated as complete assemblies, with materials and construction details specified.
With that in mind, it's quite possible that a particular fixture might be fine for one ceiling, but not another. Most assemblies use 'ordinary' fixtures.
The same applies to construction details; one ceiling might require the fixtures to be 'boxed in' with drywall, or covered by insulation, while another will not.
Is there any value to 'improving' things with, say, better fixtures? Probably not. Since the entire ceiling is tested as a complete assembly (I think the test section is something like 15ft x 20ft), a change to one small section probably won't affect the test results much.
Tom: IF you have a rated ceiling assembly, then you must provide 'equal' rating with the devices you install.
First, check with the local AHJ & determine IF the drop ceiling is in fact a rated assembly. The mfg install instructions will be a big help in this also.
IF you have to maintain the rating, the Tenmat covers are the easiest approved for maintaining the rating.
Some 'old school' metgods were placing a 'tent' of 5/8" fire code sheetrock over the top & sides of a troffer. Another was laying 'rotten cotton' insulation over the fixture. Some AHJs accepted the described ways, others did not. The Tenmat is UL labeled/listed for troffers and rated ceilings. There may be other brands, but that is the only one I am aware of.
Hotline, I must take some issue with your response.
It's what I was getting at when I said things were tested as an assembly. That is, a complete ceiling assembly.
Special fixtures? Ordinary fixtures? Ordinary fixtures wrapped in drywall? All of these are construction details specific to each ceiling. A cruise throught the UL Fire Resistance Directory *the 'orange books') will detail an enormous variety of ceilings.
Let me stress that the 'assembly' is more than just the ceiling grid. It is also the part of the building above the grid; construction details there - drywall thickness, etc.,- often are the real determining factors in the performance of the assembly.
In the actual fire tests, the real results seem to depend mpre on the grid holding the troffers in place, rather than whatever the troffer is made of. This is engineering trivia, though, and no substitute for following a tested design in its' entirety.
" The mfg install instructions will be a big help in this also."
We all should know that a rated wall or ceiling assembly is installed to contain a fire (for a period of time) from penetrating the rated assembly. The integrity of the assembly must be maintained when any penetrations are made. (Lighting, HVAC diffusers, receptacle locations, etc) There are listed/labeled (UL Tested) items to insure the rating of the assembly.
The item the OP and I mentioned is UL for fixtures within a rated ceiling.
All that said, yes, there are 'rules' (specs) within the UL rating book, which limit/guide the number and spacing requirements of all penetrations in all rated assemblies.
Following the mfg instructions for the ceiling assembly and the mfg instructions for all items used to maintain the rating of the ceiling is paramont.
The single touchiest drop ceiling I ever had the pleasure of messing with was for a Toys R Us build-out.
The Fire Marshall had his hair on fire when the retailer's all plastic and cardboard inventory, all the time, for children/fire bugs came to his attention.
So the lid was changed to fire proof and sprinklers aplenty. Further, even the gaps in the lid needed listed fire-stop.
The fixtures were mandated to be LOWER than the fire lid. Hence they could be ordinary 277v low-bays.
Correcting all of the circuit faults -- whew -- NOT fun.
Because of the Fire Marshal, EMT was preferred over MC at every turn. Getting his okay was solely based upon the level of craft and his opinion.
Why was he so picky? Just the prior month a Toys R Us burned down on the East Coast in record time. Then the word went out to all of the other Fire Marshalls: these toy stores are 'Coconut Groves' waiting to happen!