Test interval optimization of stand-by equipment

The stand-by equipment is tested periodically in order to check its condition. Latent faults are likely to be eliminated in this way prior to failure at an actual demand. On the other hand, the testing may degrade the equipment and cause failures. Through a proper choice of test interval the negative and positive effects of testing can be balanced against each other. In many cases also the economic factors need to be considered. Big losses in the case of failure on demand justify the test interval which gives the minimum unreliability. The high relative costs of testing may, on the other hand, make the longer test intervals preferable to the one giving the unreliability minimum.