Is MCBF a guaranteed period of failure-free service?
No. An MCBF has absolutely nothing to do with the minimum rated life of a relay. An MCBF is derived from live testing a large number of relays for their minimum rated life. The number of failures that occur during the testing are then divided into the total number of completed operations. • Do initial screening tests have any effect on the reliability of relays during the use life? Yes. Screening tests detect those failures, which would otherwise occur during the early life of a relay. This is why it is important to know what screening tests are performed by the manufacturer. • Is there more than one method used to calculate relay reliability failure rates? Yes. There are several methods used to calculate relay failure rates. The accepted method and three other methods that are sometimes used to enhance a particular failure rate are shown in Figure 1. Method Total Operations Failures *Failures Rate A C C E P T E D Terminate testing with a failure and one operation is one coil energized
