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 18352 - Assessment of Nonmetallic (NM) Cable Aging

Presenters: Paul Brazis, Underwriters Laboratories, Inc., Fan He, Underwriters Laboratories, Inc.  

Nonmetallic (NM) electrical cable is used in more than 80 percent of all residential structures in the United States. Currently there is a lack of quantitative data on the effect of damage, degradation, and aging on NM cable, as well as service life based on various environmental conditions. The purpose of the project is to understand how NM cable insulation degrades under thermal aging and how long it may take the insulation to breakdown at a voltage below 6 kV under a given temperature. At a voltage below 6 kV, the probability of dielectric breakdown becomes unacceptably high, increasing the probability of parallel arcing in the cable, leading to fire. In this presentation, we will discuss using normalized weight loss as the aging indicator for NM cable insulation. In our experiment, we first age the NM cable insulation under three different temperatures. Then we fit the empirical data with a summation of exponential functions and estimate the activation energies. With the estimated activation energies, we can derive a relation between the insulation breakdown voltage and the normalized weight loss. The derived aging function can also estimate the NM cable service life under variable temperatures.


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