Gripple wire style secondary support for recessed modular luminaires within ceiling grid systems; is this a requirement or just best practice? (Excluding instances where the manufacturer's installation instructions stipulate it.)
This will depend on how heavy they are and the procedure for removing them, which may vary with where they are. As far as BS7671 goes, no rule, but things like manual handling and working at heights rules also apply. I suspect the answer is 'strongly advised'
Building Regulations dictate that the ceiling must not fall down, so it depends on the strength of the ceiling and it's supporting structure. You should ask the ceiling manufacturer to confirm the ceiling can support the additional weight of the luminaires, or assume the worst case and fit your own supplementary supports.
559.5.2. Simply requires adequate means to support the luminaire and that the ceiling is compatible with the weight imposed.
I have a particular interest in fire safety and many of the incident photos I have gathered over the years show buckled metal grid suspended ceilings with luminaires dangling at the end of wires liked some latter day mass hanging.
It would seem reasonable that a luminaire of any significant mass should not rely solely on one of those soft lay-in tiles without additional support.
