Re: http://h71000.www7.hp.com/?

Dave Froble wrote:
JF Mezei wrote:

w_tom wrote:

EMP is so trivial that even an NE-2 neon glow lamp (a bulb rated in
milliamps) will make such transients irrelevant. If a transient
overwhelmed protection already inside appliances, this it was not EMP.
It was a direct strike.


This is not as simple. In the 1980s, much of quebec was thrown into
darkness because of aurora borealis a few thousand km north of montreal.
Those induced currents into the power lines from james bay and
protective circuits automatically shut then down and Hydro Québec's
software was ill conceived to automatically start load shedding and as a
result crashed everything. (our software was fixed since then, but in
ontario and north east USA they obviously had not fixed that load
shedding software a couple years ago during a hot summer's day).

The aurora borealis did not induce destructive currents, but the systems
detected an anomaly in currents and shut the line down.
Now, imagine the line between the home and the barn. Imagine that with
time, the ground at the barn becomes corroded and contact is no longer
really good and your switch there is no longer properly grounded and
some fuse blows to protect the circuits.



directly into electronics. With only one AC electric wire grounded
means AC electric is not sufficiently earthed.


Well, if you ground all three of the 2 phase wires that come into north
american homes, the electric utility will either love you because you
your huge electric consumption/bills, or will hate you because you're
shorting their grid :-)


It's my understanding, (note, I'm not an expert), that lightening doesn't travel inside a wire, it rides on the outside.

Skin effect? That's still on the conductor, just at the surface
of the wire and not in its core.


If I'm correct, then a simple grounded collar on the wire should strip the lightening off the wire, if the collar provides a better path to ground.


Doesn't the (presumably) grounded service panel locate right at
the entrance to the house do this? (I'm 99.99% sure code requires
the service panel be grounded.) All the wires run through knockouts
in the metal wall of the panel, which creates a grounded collar.

You don't physically ground all wires.


Or does each individual leg require a separate collar? Even
so, if it is that easy, you would think it would be required
anywhere there's been a lightning storm in the last 100 years.
(I.E. the entire planet except maybe parts of Anarctica!)



If you actually need to ground each conductor, the way to do
it would be through a low-pass filter with the cutoff well
below 60Hz connect to the ground, or a high-pass filter with
the cutoff just below 60Hz in series with the AC circuit, or
both. Lightning is basically DC, so I think it would
induce a large DC pulse. Electric power is AC, and would
see the low-pass filter as high-resistance. (High enough
impedance at 60 Hz and no appreciable power would be lost.)
AC would pass right through the high-pass filter but DC
would see it as an open circuit.

Whole house surge protectors seem to cost enough ($150-$200
at Home Depot) that they probably consist of filters and not
just a grounded collar.


It's been 31 years since I studied electronics, so IANAEE!

Dave, just a victim, not an expert.



--
John Santos
Evans Griffiths & Hart, Inc.
781-861-0670 ext 539
.

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