On Friday, February 10, 2017 at 2:55:15 PM UTC-5, James Wilkinson Sword wrote:
Doesn't make sense to me. ... Or do they assume all areas' usage changes together?

They do not assume. It is. And it has been well proven by generations of experience. Distribution is planned and monitored so that one transformer automatically adjustments to keep voltages within 10%.

Also denying impedance subjectively is disingenuous. Numbers were provide to demonstrate how protection works. Posted was also known and done successfully over 100 years ago.

If protectors were protecting attached appliances, then it was also protecting other appliances on the same circuit (but plugged into other receptacles). Long before making blanket conclusions from speculation, first learn how protectors work. A protector is only as effective as its earth ground. In facilities that cannot have damage, plug-in protectors are not used; sometimes aggressively banned. A 'whole house' solution is always implemented..

230 volt protector circuits all but ignore 415 volts. Since its let-through voltage is something above 500 volts. Your conclusion that protectors protected from that fault violates well understood science - and is subjective. Junk science conclusions are created by subjective reasoning. Protector components would all but ignore 415 volts. Learn about let-through voltage. Or read V-I charts in protector datasheets.

Specification numbers for those protectors were not posted and are probably ignored. Another reason why junk science is alive and well. Informed consumers alway cite numbers - especially specification numbers. Denials are best ignored when not tempered by specification numbers.

An IEEE citation (that trader_4 may cite) demonstrates in figure 8 how a plug-in protector earths a surge 8000 volts destructively through a nearby TV.. trader_4 - surges are a current source; not a voltage source as that post assumed. That means voltage will rise as high as necessary so that an incoming current will flow. Then 120 ohms impedance to earth (the outgoing current) can create a voltage approaching 12,000 volts. Or 8000 volts as that IEEE citation demonstrates.

Nobody said plug-in protectors are useless. But those near zero joule devices can make damage easier if not used in conjunction with a 'whole house' solution. As we engineers repeatedly saw - even to a network of powered off computers.

Plug-in protector is considered so dangerous that some cruise ships will confiscate it if found in luggage. It needs protection provided by a properly earth 'whole house' solution.

If a protector was properly designed, then plugs do not melt. An always required circuit breaker (or fuse) disconnects power before a fire threat can exist. Why were protectors defective - therefore melted? Where is the datasheet number that explains a completely unacceptable incident?

What is the difference between a $10 plug-in protector and an $85 one from Monster? Not much. Monster has a long history of identifying scams. Selling an equivalent product (with expensive looking paint) at much higher prices. It is obscenely profitable because so many mistakenly assume a higher price means better quality. Quality and effectiveness is found in specification - that are ignored to make subjective claims and denials.