I think the UL requires only that the MOVs don't start a fire when
exposed to conditions which cause their break-down. *They don't rate
their ability to function as "surge protectors".


UL evaluates surge suppressors for fire, electric shock and personal
injury hazards, and also measures and categorizes the devices for how
much voltage they can "clamp," thus preventing excess voltage from
passing through to electronic equipment. UL refers to this as a
"suppressed voltage rating," with ranges from 330V (volts) to 4000V.
Believe it or not, the lower the rating, the better the protection.

Whatever surge suppression protection you're looking for, make sure
the surge suppressor has been tested and Listed to the stringent
requirements of UL 1449, the Standard for Transient Voltage Surge
Suppressors.

http://www.ul.com/consumers/surge.html

http://ulstandardsinfonet.ul.com/toc...=s&fn=1449.toc