According to PrecisionMachinisT :

"Robert11" wrote in message
...

Thanks for such good info.

BTW: When an MOV fails due to being unable to dissipatge too many Joules,
or overcurrent, how does it fail ? As an open or as a short between the
lines it was trying to protect ?

These short the line so that the fuse blows out, thus effectively
disconnecting the load from the power source.

MOVs generally fail _open_, and the fuse don't blow. That's why most
protective devices have LEDs - to tell you whether the MOV is fried
or not.

Consider the situations under which they trip - very high transient voltages
and effectively an arc. The guts of the MOV are destroyed.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.