High-voltage contactors are electromechanical devices with finite life governed by both mechanical endurance and electrical stress, which makes a single universal Mean Time Between Failures (MTBF) or Failure In Time (FIT) rate difficult to assign. This application note provides a framework for predicting dependability by modeling reliability from the application environment and the physics of contact wear, using metrics like MTBF, FIT, and the bathtub curve. It also makes the economic case that purchase price is often a small fraction of total cost of ownership, since eroding contacts raise contact resistance and I²R heat losses while reliability drives service and downtime costs. The note is aimed at system integrators who need to predict service intervals and justify component selection on a TCO basis.
