I could not even begin to guess how many relays we have sold over the years.  Relay failures are extremely rare for both mechanical and solid-state relays.  We always try to work with our customers to choose the correct size of relay for a given load, and to determine the cause of failure on those rare occasions.  The majority of relay failures we have seen are related to overcycling the relay (turning the relay on or off far more frequently than rated), lightning strikes, and of course your basic misuse (too much current or voltage flowing through a heavily cycled relay).  There is this misconception that mechanical relays will wear out prematurely, and that solid-state relays should be used instead.  Rarely have we seen a worn out relay.  Many mechanical relays have a cycle life in the millions, and we have seen no evidence to suggest a mechanical relay is any more or less reliable than a solid-state relay.  Long-term reliability is generally controlled by choosing the correct relay size and making sure the proper protection is used across its lifecycle.  Relay life spans exceeding 10 years are possible, one of our original customers contacted us to let us know that one of our first relay controllers (from 20 years ago) is still fully operational.

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