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Project: 306 #U415
 

Abstract/Conclusions/Recommendations The effects of increasing levels of thermal insulation on the life, safety and reliability of electrical wiring used in older dwellings were assessed. Simulated ceiling sections were assembled to determine temperature rises experienced by the older 60 degrees C rated NMD-1 and NMD-3 as well as 90 degrees C NMD-7 connected to flush mounted light fixtures and insulated with cellulose, fiberglass and polyurethane foam insulation. Under the highest levels of thermal insulation investigated (RSI 7.0), temperatures vastly in excess of the cable rating were encountered for NMD01 and NMD-3, particularly within the light fixture, even without exceeding the allowable cable ampacity. Infrared thermography was used with success to determine temperature profiles along the cable runs. The aging characteristics of NMD-3 and NMD-7 were determined by accelerated oven aging, highlighting the brief life (about 4 years) at rated temperatures. A model was developed to combine the actual field temperature computed from circuit loadin gand the wire aging characteristics to derive probable service life of the wiring system.