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Eric[_6_]

wrote:
In alt.engineering.electrical Don Kelly wrote:

| Now - is this all germane to household protection? You say not and I agree
| with you- because household equipment can ride through - at worst- doubling
| of the clamped voltage for a very short time even though the clamped voltage
| is relatively small compared to the peak of the incoming surge. --

What if the surge is an extreme case (e.g. direct strike very near) and it is
arriving at protection devices in common mode (same polarity on all three
wires). Bud's assertion _seems_ to be that no surge could ever be of the
type with substantial energy at high frequencies. My belief is that they
can, and will at times. Lightning strokes have that energy, or else you
would not receive them on UHF. If the stroke is strong _and_ close (e.g.
less line inductance between the point of strike and where it is being
considered), then more of that UHF energy will arrive.

I have seen damage patterns in electronics that strongly suggests that there
were specific paths involved based on minor levels of reactance in the circuit.
A resistor would be melted along one path, but not so along another which had
a small inductor (3 turns in air) in the way. And this device (a VCR) was on
a surge protector along with a TV that was unharmed.

If Bud is just arguing about the _typical_ (median?) surge level, then maybe
we are arguing apples and oranges. I certainly don't intent to protect against
50% of surges. My target is better than 99%. I want to feel comfortable
sleeping through a severe thunderstorm while my computers and media center
remain plugged in.

I do agree that things can survive at the clamping voltage. But there has to
be a clamping situation. It's too easy for a surge to come in as a common
mode surge where the voltage difference across the MOVs would be (nearly) zero.
Then all we have is a propogating wavefront. And if it is strong and/or close
then we have very fast rise times. And it passes by the MOVs "laterally".

There's probably a big difference of opinion about just how much protection is
worth it. But one thing I do see in at least part of this thread is that Bud
focuses on quoting things other people say, and does very little to express
things in his own words. That suggests he reads but does not fully understand.
And that means I can't ask questions of what is said in the thread. Since Bud
can't (or won't) defend what he's saying in his own words based on his own
knowledge, it's not really a two way street. His "experts" are not involved
in the debate; they can neither defend their position nor be questioned about
it to get more details.

It also has brought some other comments from people who are either anti-social
insulting types, or those that just don't understand what is said (apparently
having never dealt with transmission line propogation), or both. But at least
I know who not to trust any technical opinions from when I have question to
ask about things I want to learn more about.

I can attest to vhf/uhf content in lightning strikes. I worked for a
communications outfit. We owned and maintained a number of comm sites
with towers and antennas. One strike on an antenna destroyed the LDF rf
cable all the way to the polyphaser at the bottom of the tower. It had
blowouts at about 1 foot intervals all down it's length suggesting a
1/2 wave of about 1 foot or approx 460 mhz. That's one hell of a lot of
energy at that frequency..
Eric