The electrical network consists of the overhead and underground cables which link the electrical generation facilities to the large urban consumption centers. The flow of current is controlled by many electrical apparatus of various types. The circuit breaker is one of the most important, and since its main function is protection, its reliability is particularly important. It may be quiescent for long periods and called upon to interrupt high intensity short-circuit currents in a fraction of a second. Strict operating rules and sophisticated testing methods are established. One these testing methods is timing, which is the measurement of the mechanical operating times.