life time of relays
As been said before generally all small ctrl relays are all "on condition" as lifetime limit. However all the big power ctrl relays and line contactors are life timed with flight hours or/and elapsed time. These are the only relays that are so called serialized that meens with seraial number on and can be tracked down in maintenace computersystems for installation time and ammount of flight hours accumulated. All other relays are so called consumable sparepart with no serial number and no tracking of accumulated time and therfore changed only when they fail. This is a general rule for most aircraft types.
Regards
wings 1011