Over the years I have replaced dozens of MOVs in my
numerous high-end surge-limiting power strips rather than
shell out another couple hundred dollars for new strips
after major power company events. I get on average a year's
life out of the strips before another power company event
comes along.
The cause of some of these events is known. Another
power company had three-phase lines going over the
street-side power lines. Under certain wind conditions they
would make contact. I observed a large, long 1/2 second
over-voltage event that blew out the breaker panel
suppressor and at least one MOV in each power strip with a
bang and smoke.
Other times lightning would induce the event. I
theorize that a flashover resulted in a nearby power company
voltage regulator's (a big variac) storage of a large amount
of energy due to large following currents. Somehow this
energy then dumps onto the street-side lines, causing
another failure of the surge protectors. The power company
regulator also failed to 8% high and this may have
contributed to the problem.
But the AC system and major household appliances were
not damaged. This indicates that while there was a serious
over-voltage, it was not enough to pierce the insulation on
motor windings and an unprotected wall wart.
Anyway, I bought a few dozen replacement MOVs and 3 or 5
amp pigtail fuses for repairs. Usually just one MOV and
fuse fail per strip. The strip can be recovered with
sufficient skill.
Good surge protector strips have inductors in them to
block the high frequency components of the surge.
Otherwise, plugged-in power transformers without effective
shielding between the primary and secondary (typical) can
pass along these potentially large high-frequency components
to the following circuitry.
In my case, 130V MOVs for the 125VAC service would blow
out at the next event. So I upped the replacements to 150V
with some hope that it will make a difference.
The replacement fuses are standard AGC 250V sized at 3
or 5 Amp. They really take a beating when one of these
events comes along. The inside surface of the glass fuse
body has lots of metal globules embedded in the glass.
Professional lightning protection systems use a
multi-layered approach. It used to be that Polyphaser Corp
sold a book called "The 'Grounds' for Lightning and EMP
Protection" that described this in usable engineering terms.
Now they don't offer it on the website as far as I can tell.
Just salesman's faqs.

Henry










As a result of recent events, I have two surge protectors that no longer
function without putting out loud noises on HF. I found that the $5
surge protector that my Yaesu was plugged in to was making a loud
whistling noise which was covered up by the louder warbling noise being
made by the Belkin I had my computer plugged into. So I decided to break
them open to see what was inside. The easiest was Old El Cheapo, held
together with screws. Inside was a length of wire, a switch and ONE disc
capacitor wired into six plugs. IMO that's little better than a plain
old power strip. The Belkin had no screws, so it took a little longer to
crack. The results: a switch, two LEDs ("protected" and "grounded"), an
inductor coil, a couple resistors and transistors, and about 9 or 10
disc capacitors in series. In October 2002 the Belkin cost me $40. I'm
hard pressed to say that it was money well spent, if all that's in there
are some capacitors and resistors. Question: are surge protectors worth
it if all they are is just a bunch of capacitors? I know that my $40
surge protector apparently rolled over and died when hit with a real
surge.



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