Don Kelly wrote:
----------------------------
"Tony Hwang" wrote in message
news:dncTj.112858$rd2.31639@pd7urf3no...
wrote:
In alt.tv.tech.hdtv Michael A. Terrell
wrote:
| Bull****. Like ALL charges, it simply seeks a complete circuit to
| flow. You have absolutely no grasp of the basic concepts, yet you
| continue to spout your ignorance and lies.
Not true.
When you close a switch between a power source and a pair of wires that
go
out yonder, the electrical energy does not "know" whether the circuit is
complete or not. If it refused to flow, it would not be able to find
out.
It will flow, whether the circuit is complete or not. What happens after
that depends on what is at the other end, which could be an open
condition,
a short circuit, or some kind of resistive or reactive load.
You've claimed to have worked in broadcasting in an engineering role. So
you should understand what happens at the end of an open transmission
line.
The electricity flows to get to the open end. Yet it is not a "complete
circuit".
Hmmm,
You seem to be confused between current flow(energy) and voltage(poential)
Nothing flows in an open circuit. If not we have to rewrite Ohm's law.
Show your credential to make a stamement like that.
Shameful.
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Actually, you are showing some confusion. Phil is right in that he is
bringing out a point that normal lumped RLC circuit theory doesn't handle
because it essentially treats the speed of propagation of electrical signals
as if it were infinite- which isn't true.
.
2)Also, on energizing a line whether it is open or closed, there is a
current flow as the applied voltage "sees" the characteristic impedance of
the line (wire or whatever) so a current will flow-even on an open circuit-
until there is a modifying reflection from the termination. For a house the
distances are such that this may be of the order of 0.1-0.2 microsecond.
After all such reflections at terminations have ceased or are negligable,
conventional circuit theory is applicable.
In these situations, you are dealing with wave propagation rather than
conventional circuit theory.
This is the regime that is of interest in considering "surge protectors"
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.
All are long relative to 0.2 microsecond, so wave propagation should not
be relevant for household circuits.
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."
What reason is there to believe wave propagation is relevant to house
circuits?
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.
--
bud--