The jist of it is the surge needs to be handled between the surge source and device. So a whole house protector will handle outside to on premise but will do nothing if your washing machine spinning down causes a brief 200V spike on the 120V line etc. The local suppressors are not typically as strong as a whole house but will sink that 200V to ground.
Apparently they have played you with numbers. For example 120 VAC in normal operation routinely 'spikes' even to 180 volts. So 200 volts is simply an additional 20 volts of noise. Noise made irrelevant by protection inside every appliance.
Or is your washing machine, refrigerator, dishwasher, and air conditioner blowing out clocks, dimmer switches and GFCIs daily? Myth purveyors will hype noise into massive and destructive surges. Numbers only define irrelevant noise.
Surge protectors ignore voltages below 330 volts. That threshold voltage is printed on every box. What would a protector do when the washing machine spikes up to 200 volts? Completely ignores it; does nothing.
A rookie mistake is to think a protector somehow 'blocks' a surge. Move a power strip protector to any other wall receptacle on the same circuit. Protection remains electrically same. Does not matter if current is powered through a protector or from some other receptacle on the same circuit. Protection remains unchanged.
Only protector that protects from all types of surges - external or an often fictional internally generated one - is an earthed 'whole house' protector.
'Whole house' protectors are not the entire solution. As IEEE standards note, it only does 99.5% to 99.9% of the protection. You might add another 0.2% by putting a protector on the appliance power cord. But then equivalent protection is already inside each appliance. What was accomplished by spending $25 or $80 more? Especially when destructive surges occur maybe once every seven years.
To promote myths, they also forget to discuss superior protection already installed on every phone and cable - for free. For cable, a wire from cable to earth ground is best protection. If that wire meets important requirements such as no sharp bends, as short as possible (ie 'less than 10 feet'), etc. Telephone/DSL wires cannot connect directly. So the telco replacement that wire with a 'whole house' protector - for free.
Due to protection already on communication wires, then they are also a best and destructive connection to earth; IF the homeowner has let a surge enter. A most common and destructive path is a lightning strike far down the street to AC electric wires. Incoming to every appliance. And outgoing to earth on appliances that connect to the telephone or cable. The incoming and outgoing paths must exist to have damage. Where does damage often occur? On the appliance's outgoing path - the telephone or cable connection.
Just another reason why protection is always about earthing that current BEFORE it can enter. And a type of surge that no adjacent protector claims to protect from.
Did they also forget that ethernet interfaces are designed to withstand more than 1000 volts?
Myths convert appliance generated noise into massive and destructive surges that somehow forgets to damage dimmer switches, clocks, and smoke detectors. Somehow a protector that ignores voltages below 330 volts will eliminate noise from a washing machine? Same myths also forget to mention superior protection required and existing on all telephone and cable wires.
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