When is it required to use fire stop insulation on horizontal runs?

[bjp_ne_elec]

I was trying to find the code reference where it deals with multiple NM running through the same bored hole, and then noticed all the various threads brought up fire stopping. I don't do much house wiring but I have firestopped vertical runs but have never been called out on an inspection to firestop horizontal runs. Most houses in NE use strapping so essentially the area between floor and ceiling is open. I do have a job coming up where it has solid floor trusses so want to get this understood.

 

[augie47]

Just for clarification: 334.80 discusses derating for NM where the cables run through openings in wood framing that is to be fire or draft stopped using thermal insulation, caulk or sealing foam so the rule is applicable for more than just FIRE stop..
334.80 also discusses multiple Romexs without spacing in contact with insulation