NBS Tests Insulation
Tests conducted by National Bureau of Standards (NBS) researchers have found that closed barriers above recessed lighting fixtures can cause the fixtures to operate above the safe temperatures specified in the National Electric Code.
NBS also found that the addition of minimal insulation over a surface-mounted lighting fixture containing two or more rated lamps, can cause normal household branch circuit supply wiring to operate above its specified 60°C rating.
Overlamping will cause even higher wire temperatures. If there is insulation over the fixture, overlamping, and an additional 15ampere load current, findings show that the temperature of associated branch circuit wiring will exceed 80°C for one lamp fixture and 100°C for fixtures with two or more lamps.