AbstractA test has been devised to detect incipient failure of relays, which does not require removal of the relay from its circuit, nor does it require any system outage time in vital reactor applications. The relay parameter, which is evaluated, is the actuation time. The distribution of actuation times has been measured for several relays, of two different types. The distribution has been shown to shift as a function of coil voltage, overall temperature, and spring tension. A large shift in the distribution was noted as a result of a destructive heating test. As a result, the use of the 90% spread points of a reference distribution is proposed as a criterion for the detection of incipient failure in a periodic multiple-test program.