160915-1152 EDT
Following is a very good discussion:
http://www.littelfuse.com/~/media/e...n_devices_and_principles_application_note.pdf
Transient limiting can work at energy levels up toward the energy rating of the transient limiter (this is a power dissipation, temperature rise, within the transient limitier problem), and probably tolerate up to that energy level for a large number of hits.
When the energy level rating of the limiter is reached, then the number of hits tolerated at this levrel is probably greatly reduced compared to lower levels. How a manufacturer defines their rating will define what to expect.
Go some ways above the nominal rating and failure (exploding) will occur on 1 transient hit.
Recently I had two tramsient limiter outlet strips fail the same day, almost certainly at the same instant, These were on two different circuits at opposite ends of the house from the main panel. Both limiters had internal fuses of some kind that opend when the MOV failed. Thus, the load was disconnected from the source.
Parallel MOVs were used in the outlet strips. Only one or two MOVs failed in each case. The outlet strips were different brands. Essentially both strips were destroyed, and both had been in operation for possibly 16 or more years.
To make valid statements about MOVs or other transient limiters you need to underestand what are their characteristics, how do they limit transients, and really how big are transients after limiting. The Littelfuse discussion provides you good information.
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