Effect of Historical Trends, Equipment Age, and Maintenance on Circuit Breaker Failure Rates

Circuit breakers are among the more ubiquitous devices found in all types of facilities. Even small buildings can have hundreds of them, quietly and vigilantly protecting personnel, equipment, and critical functions. But circuit breakers fail - and how they fail matters. This paper shows that failure rates have varied historically, that failure rates change as a function of equipment age, and that failure rates respond to preventative maintenance activity, often counterintuitively. These results are much more transient than previously understood, often varying by an order of magnitude or more. Our current assumptions about maintenance and failure may very well do harm to our facility electrical systems. The U.S. Army Corps of Engineers collected and analyzed a database of equipment records over several decades. This paper includes several thousand unityears of circuit breaker information, giving specific performance detail under more clearly defined circumstances. Point estimates provide mean device performance statistics, while figures show unpublished details of circuit breaker failure that provide more information to facility managers and design engineers.