Originally Posted by oppopioneer
This was posted to me in PM by a qualified electrician, his name will be kept hidden so I'm not plagiarizing.
... "One disadvantage to MOVs is that they deteriorate over time where there reaction time is slower and not as much energy can be diverted. Their Joule rating is the maximum energy they can divert over the life of the product,
Common myths promoted by lies in places such as HowStuffWorks. First, MOVs do deteriorate. That is a fact provided without numbers. To have reality means including numbers.
To fail catastrophically, power strip protectors grossly undersize their joules. Then when a failure occurs (when the appliance is left to defend itself from the surge), the naive consumer recommends that scam. One reason why Monster (a company famous for its scams) is also selling plug-in protectors.
All appliances contain superior protection. A surge too tiny to overwhelm the appliance, also easily destroys the protector. A massive sales increase result when people use only observation to know something.
Catastrophic failure (including failures indicated by its light) is completely unacceptable - as even made bluntly obvious in MOV datasheets. Such failures exceed "Absolute Maximum Parameters". Completely unacceptable.
No protector must fail catastrophically. Normal failure mode for a properly designed MOV protector is ‘degradation’. Its voltage (Vb) changes by 10%. A normal failure mode cannot and is never reported by its indicator light. Indicated failure implies a protector was probably useless when bought. A profit center.
How much is required to degrade a protector? One MOV datasheet describes testing:
> The change of Vb shall be measured after the impulse listed below is applied
> 10,000 times continuously with the interval of ten seconds at room temperature.
But again – numbers. An example of what a protector must do when properly sized. More reasons why a homeowner spends less money for a properly sized ‘whole house’ protector.
Or include numbers from the IEEE Green Book entitled 'Static and Lightning Protection Grounding':
> Still, a 99.5% protection level will reduce the incidence of direct strokes from one stroke
> per 30 years ... to one stroke per 6000 years ...
Ballpark numbers for discussing the life expectancy of effective protectors. MOVs fail mostly because that protector was a profit center; not surge protection. Spend $7 in a grocery store to have a similar plug-in protector circuit (and similar specs) so often hyped by Monster for $100.
MOVs fail quickly when that gets the naive to recommend an obscenely profitable protector. MOVs failure mostly promoted when one forgets that numbers must always be included in any statement or recommendation. Recommendations without numbers is why junk science exists.
Second, he is right about MOVs being so effective when connected short to earth. But did not learn other critically important facts and numbers.
Why do Panamax, Monster, Belkin, etc provide a joules number. They do not claim protection from destructive surges. Would rather not provide a number that says inferior protection. That number, found in the datasheets from all MOV protector manufacturers, is provided only because UL requires it. To do human safety UL testing, a manufacturer must declare up front to UL what is inside. Meanwhile, those protectors make no other protection claims.
How do hundreds of joules (near zero) in those power strip protectors absorb surges that a hundreds of thousands of joules? It doesn't. Tripplite et al do not claim effective protection. Those joules numbers say so. UL required number says it is near zero surge protection. A power strip manufacturer will not say anything more. Otherwise you might learn it is an ineffective protector; only a profit center.
Two posts that provide many ‘ignored’ numbers for MOV protectors. Third will discuss how a Surgex works.