The breaking of currents from a couple of amperes to several tens of kilo-amperes is a main function of medium voltage circuit breakers. Vacuum has become the leading technology in this field with attributes such as high reliability and superior electrical endurance. Standards and specifications define testing procedures to demonstrate the electrical life of circuit breakers. The requirements vary from a couple up to several hundreds of interruptions. The paper discusses the results of electrical endurance tests on vacuum interrupters according to different procedures with emphasis on their severity and the actual life time expectancy of vacuum interrupters. The results show an almost unlimited electrical life at load current level and a short circuit life expectancy exceeding any standard. The arc control and current level turned out to have a strong influence, too. Differences could be shown with respect to the different test procedures.