Industrial equipment, more specifically the individual components that make up the piece of equipment, age at different rates.  A system that includes drives, motors, power supplies, monitors, and sensors that work together to complete a task, will all have elements fail at different times in part because of the different dates of manufacture of each piece of equipment but also because of differing levels of stress that the internal components of the equipment are subjected to. A Variable Frequency Drive (VFD) outputs higher voltage and current to a motor than say a power supply outputting to an analog relay board. The everyday high voltage and current the VFD operates with will reduce the life of unit much more quickly than the power supply does. Electrolytic capacitors tend to dry out, electromechanical relays tend to have dirty contacts, batteries tend to discharge while at the same time most semiconductors tend to age very well showing virtually no signs of degradation due to aging alone.