On Apr 20, 10:57*am, Jim Redelfs
wrote:
I have been following the Intermatic thread with some interest. *
Admittedly, it got a bit "deep" when the engineers began debating. *
Still, I gathered much good information, not the least of which was that
MOV (metal oxide varistor)surgesuppressors "wear out" over time - that
their efficacy diminishes with eachsurge.

If an indicator light reports failure, then surges far exceeded what
that protector should have ever seen. Properly sized protectors only
degrade - normal and acceptable failure mode as listed on manufacturer
datasheets. Degrade means indicator light reports no failure and
protector remains functional.

Failure light indicates a failure that a protector should never
experience.

Surges occur typically once every seven years. A number that can
vary even within towns. A number also changed by things such as
geology or even buried utility pipelines. Do not even assume
mountaintops suffer more surges.

How frequent were your surges? Best answer comes from canvassing a
neighborhood for damage history over the last decade. Chances are
surges were so trivial that the protector earthed them with near zero
degradation.

If surge damage is frequent, then a larger 'whole house' protector
(higher joules) could also be installed and earthed. Both properly
earthed protectors mean a significant decrease in 'degradation' inside
each protector - longer life expectancy.

In most situations, a 'whole house' protector is good for decades.
If not, a larger joule protector is installed so that it does not
degrade for decades.

Why do MOVs have a bad rap? A plug-in protector maybe so grossly
undersized that a light even indicates the unacceptable failure - MOV
violated manufacturer acceptable operation. A protector must be
properly sized so that it never reports failure on that indicator
light. Light will never report a degraded protector. Light simply
tells the human that he has installed a grossly undersized and
unacceptable protector for that location; that the protector did not
provide effective protection.

Let's put some numbers to life expectancy. For a 100A surge, life
expectancy of a 45 joule MOV is 2,000 surges compared to 80,000 for
the 382 joule MOV. 8 times more joules results in a 40 times increase
in life expectancy. A joules increase, protector life expectancy
increases exponentially.