Reno:
I dd not stress this but...
" 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.
