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14 <br />III. Outage Causes <br />Equipment failure, extreme weather events, wildlife, and vegetation are some of the most <br />common causes of electric system outages. However, certain factors, such as regional <br />weather and animal/vegetation patterns, can make some causes more prevalent for a <br />specific group of utilities. The following section of this report includes graphs depicting <br />common causes of outages for your utility, all utilities in your region, and all utilities using <br />the eReliability Tracker. <br />Charts containing aggregate information are customer-weighted to account for <br />differences in utility size for a better analytical comparison. For example, a particularly <br />large utility may have a large number of outages compared to a small utility. To avoid <br />skewing the data toward large utilities, the number of cause occurrences is divided by <br />customer size to account for the differences. In Figures 8-13, the data represent the <br />number of occurrences for each group of 1,000 customers. A customer-weighted <br />occurrence rate of "1" means one outage from that outage cause occurred per 1,000 <br />customers on average in 2020. <br />Note that the sustained outage cause analysis is more comprehensive than the <br />momentary outage cause analysis due to a bigger and more robust sample size for <br />sustained outages. Regardless, tracking both sustained and momentary outages helps <br />utilities understand and reduce outages. To successfully use the outage information <br />tracked by your utility, it is imperative to classify and record outages in detail. The more <br />information provided per outage, the more conclusive and practical your analyses will be. <br />262