In alt.tv.tech.hdtv bud-- wrote:

| The last standards for simulating typical surge waveforms I have seen
| (IEEE) were
| 1.2 us rise time, 50 us duration
| 8 us rise time, 20 us duration
| a ring wave with a frequency about 100kHz.

So now you are saying these figures represent a typical surge waveform,
as opposed to the worst case waveform you said a long time ago.

The term typical is generally accepted as a median. That means half of
the surges would have a slower rise time, and half would have a faster
rise time.

My concerns are not the typical surges. I suggest that half the surges
don't even need protection at all; they won't cause damage even if there
is no protection. But that also means half can be damaging and need the
protection. And a fraction of those surges need _substantial_ protection.


| All are long relative to 0.2 microsecond, so wave propagation should not
| be relevant for household circuits.

Maybe for the typical surge. How about for the most energetic 1% that are
the ones I'm most concerned with because they are hard to protect against.


| A favorite article from w_ also uses a "8x20 us impulse as a very rough
| representative pulse" with most harmonic content from 20kHz to 100kHz.
|
| Martzloff, using the shorter rise time, has written: "For a 1.2/50 us
| impulse, this means that the line must be at least 200 m long before one
| can think in terms of classical transmission line behavior."

And this statement is only using 1.2/50 us as an example. If you think
such a timing is the standard, why not offer a quote that actually says
that?

What does the "/" mean in that case, anyway? I never got to ask you that
before. Does it mean "divide 1.2 by 50"?


| What reason is there to believe wave propagation is relevant to house
| circuits?

The most damaging surges (not the typical ones) have substantial fast rise
high frequency energy (such as due to a very close direct contact strike).
In these cases, even if you can remove all of the low frequency energy, there
is still damaging energy in the higher frequencies that do follow transmission
line behaviour not only in wiring lengths of typical homes, but even in wiring
lengths inside a small appliance like a computer modem.


| As to the advantage of "whole house" vs local surge protection, "whole house
| protection depends on distances to all "protected" items being small.
|
| Longer distances make the system more subject to effects like direct
| induction from lightning into the wiring. I don't see why, in general,
| the distance has to be small.

I believe he was referring to the distance between the whole house protection
and the ground/earth electrode.

For things like the service drop distance and the branch circuit distance, it
can be a tradeoff between different kinds of surges. The longer wiring will,
through its self-inductance, reduce the high frequency energy and slew the
rise time of the wavefront ... especially for common mode surges. However,
that same longer distance increases the potential level of induced surges
where the wire is effectively an antenna.

--
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