Contactors/ Solenoid/ Relays

Too broad of a question. There are some designed for very long life, others designed for very specific life spans. The range could be anything from a matter of weeks to a matter of decades.

Some of these devices are rated for so many thousands or millions of operations. You can then estimate their life by how often they operate.

Look for the MTBF of the specific item you need the information for.

We can't help, we don't know what equipment your using.

Yes - the question is too general in nature. There is vast difference in expected life of each of these devices which themselves come in a vast variety. For example relays are available in a few different types - the conventional electromechanical relays, SSRs. Life for each varies widely from that for the others. For example, a conventional relay is usually rated for a few tens of million cycles whereas the SSRs are usually rated not by number of cyccles but by life in service. Again, the life depends on the operating current. So it is not possible to get an answer to a general question that you have put. However, the manufacturers of these devices are pretty clear about the kind of life a user can expect under a set of conditions - just consult the relevant manuals.

One reason is bad quality power supply like harmonics,spikes,surges,sags, interruptions, varying voltage/frequency etc. Other is bad quality materials of construction,labour, testing,certification etc. Third is not operating or maintaining it

As others have said, life expectancy depends on far too many factors.

As to the mode of failure, (specific to contactors and contactor-relays)

1. Vanishing of the magnet airgap which will prevent the device from dropping off when coil supply is removed. (AC coils only).

2. Erosion of silver-alloy tips to such a level that (a) contact pressure is far too low and/or (b) the base metal is exposed to arc, resulting in contact welding.

3. Excessive soot formation in the arcing area resulting in creepage failure.

4. Failure of magnet rivets resulting in fraying and spreading of laminations, sometimes jamming the moving magnet and burning the coil (AC only)

There are many more, but these are common.

Maintenance records will give some insight, so have a chat with the head of maintenance at the facility for pointers in the right direction.