A very long time ago, I was at Radio Shack and a guy's wanting a refund for his Micronta analog multimeter.
It had literally exploded, the range switch blown out.
The guy had put it on amps, stuck the probes in an outlet to see if he was getting 15A like the breaker's rating
Store manager gave him a full refund, and almost kicked me out of the store for mumbling 'WTF did he do?!'
I wondered the voltage rating on the PTC "03M" seems to be
Apr MZ31 series. Epcos PTC's are all blue,
B59886C012 is a 500V 12mA part.
Other meters use a GDT but I think these are slow to ionize, and compared to your impulse generator, MOV's maybe fast enough.