Lightning protection gagets

[phil b]

These seem to be 3 phase lightning protectors. They are government surplus. How do I test them? Is there a way to determine what how much voltage they will take without blowing?

[Opera House]

Frankly, use them in your circuits for decoration and tie offs.  If you have a meter that can measure capacitance, check that.  MOVs will have a measurable capacitance.   Spark gaps and gas tubes won't.  Other that that, you will need a supply that will likely have to go to 2KV or more.  Doubt they would protect much of what you have.