[RndTbl] Power bar/surge suppressor

Hartmut W Sager hwsager at marityme.net
Mon Jan 29 11:42:40 CST 2018

I'll weigh in with 3 decades of (some) knowledge here, having studied and
sold these things once upon a time.  First of all, the insurance and the
actual performance/reliability are totally separate, though both are
typically higher as the price rises.

Above a certain price point, it became fashionable to offer insurance as
described by Rob below, but this was for marketing purposes, and, like all
insurance, is based on a statistical gamble.  I.e., a few cases will arise
where someone's equipment behind a surge suppressor (no matter how good)
gets damaged, and the suppressor company or the insurance company involved
can statistically afford to pay those in the overall income/expenses

Trevor's tech comments are completely correct.  There is no natural
time/usage-based wear-out of any of the components, but they can wear more
if the stresses (surges, etc.) are more frequent or more intense, and many
models may indeed need to be replaced after a lightning strike nearby or a
nasty surge.  Some of the better models try to self-identify (and alert you
to) failure/end-of-life.

Now, back to the original power bar question.  As for the actual
components, virtually all power bars up to about $50-70 use nothing but a
pile of MOV's (metal oxide varistors), which look just like simple
thin-blob capacitors.  The price of the power bar determines how many MOV's
are used and how much surge each MOV can dissipate (hence a joules rating
expressing how much energy can be dissipated in a very short time), and the
price also determines whether only the hot-to-neutral voltage is protected
or also the hot-to-ground voltage.

MOV's are rather crude devices that usually "clamp" above 300V (120V AC
peaks around 170V), so they are quite unsuitable for low-voltage surges of
longer duration, but they are excellent for extremely short high-voltage
surges, especially since they (MOV's) have an extremely quick response
time.  Longer high-voltage surges will of course fry the MOV's.

Higher-priced devices, beyond the typical power bars, use all kinds of
additional components beyond MOV's, and thus can have much better
characteristics all-around.

Hartmut W Sager - Tel +1-204-339-8331

On 29 January 2018 at 10:12, Rob Guderian <rob.guderian at gmail.com> wrote:

> Some surge suppressors say on the box that they 'guarantee' it, and
> make it sound like they will replace your equipment if it fails to
> suppress the power surge. I haven't read one in years, but I believe
> they do have a limited amount of time they [would/might/should] be
> willing to honour that guarantee.
> Advice: Look for it if you're buying one. The cheaper ones definitely
> don't have one, the better ones should.
> On Mon, Jan 29, 2018 at 3:10 AM, Trevor Cordes <trevor at tecnopolis.ca>
> wrote:
> > On 2018-01-28 Kevin McGregor wrote:
> >> Hey, what's the prevailing opinion on power bars with built-in surge
> >> suppressors? How long do they last? Should they be replaced every,
> >> say, 5 years?
> >
> > Never heard of a lifespan for those things.  I'm an APC partner I'm
> > sure that they would have been blasting that in all their emails and
> > "APC Currents" mag, etc, all the time if that had been the case.  Also,
> > would make their lifetime warranties on their good surge bars a bit
> > silly.
> >
> >
> ​​
> The only thing I've ever heard is replace them after a lightning strike
> > nearby or nasty surge.
> >
> > Then again, you made me think about it and perhaps the passives in
> > these things could wear out with old age??  I'm pretty sure there's no
> > electrolytic caps in them ;-)  and there's not much heat generation,
> > so all the other passives that could be in there should last like 30+
> > years like 80's computers have.
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