I was troubleshooting a burning smell when I pulled back a piece of paper-backed insulation. The insulation had a black mark about 18" long where the romex had burned it, and the romex had brown burn marking on the romex for about 18". (These are 120 volt fluorescent fixtures with magnetic ballasts). The ballasts were very hot to the touch but the whole circuit was drawing 4 amps. My thoughts are that the heat from the ballasts caused the burning. Has anyone else come across this before?