If the high voltage is still testing good, it sounds to me like they may have switched too much power and/or carried too much current. Carefully break open the reed switch capsule and look at the contacts to see if there is any sign of pitting or burn marks right on the end of the contacts where they come together when the contacts close. If you see this, you will need to find out exactly what the customer is applying to the contacts and/or what he is carrying across the contacts. There are a few things that the customer can do:
- Add some series resistance in the direct line of the reed switch to reduce the max switching current.
- Check for any added cable or wire that adds stray capacitance.
- Make sure there are no common mode voltages present.
- Also, in his application, is it possible to switch the contacts dry (no voltage or current) for maximum life. This may not be possible.
- If the customer is switching some capacitance, can they add some inductance in series?