[matthiasl]

"What is the mechanism that increases risk for MOV-sourced fires in this arrangement?"

I wondered the same thing, and failed to find a satisfying explanation.

I can find plenty of reports of MOV fires, especially in situations where there's a persistent over-voltage, e.g. a 120 V site actually having closer to 240 V due to a floating neutral. But I don't see how chained MOVs make that worse in general. This blog post has some nice photos:

https://www.electrical-forensics.com/SurgeSuppressors/SurgeS...

[consp]

No clue about the actual reliability of this[1] article but the mechanism mentioned (new pathways due to changes in crystalline structure due to uneven heating) sounds possible.

1. https://incompliancemag.com/how-and-why-varistor-failure-occ...

Reread your wondering and now conclude its about chained situations which this also does not answer.