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

John Santos wrote:
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.


Can also induce surge on non-protected ports like speaker lines causing equipment failure.


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


Can also be carried on the center conductor of coax.


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.


A 'collar' would not likely increase the wire inductance significantly and the increased inductance wouldn't block a lightning induced surge. A collar wouldn't provide a path to ground unless there was a conductor to grounded collar arc.


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.


Surge protectors generally use MOVs - metal oxide varistors. A MOV is essentially an open circuit until the voltage goes past a knee in the characteristic curve, then the current rises very rapidly with increasing voltage. They clamp the voltage across the MOV. They are like a bidirectional Zenier diode.

In a service panel surge protector MOVs are connected L1-L2, L1-N, L2-N. The neutral is earthed. When a surge hits, the voltage to neutral-earth is clamped which causes a very large current to earth (maybe 100,000 amps). Ground potential to 'absolute earth potential' can rise thousands of volts, but phone, CATV and other signal wires are clamped to the grounded neutral through phone NID and CATV entrance block and all the wires ride up with the power conductors.

Plug-in surge suppressors clamp the voltage H-N, H-G, N-G (and signal wires should go through the protector and be clamped to surge protector ground). The voltage between wires is clamped to a value that is safe for connected equipment.

High current and a clamp voltage mean a MOV will absorb and dissipate energy. If the energy is over the MOV rating the device will fail. They also progressively degrade when hit with large surges.

Lightning produced surges are short pulses, maybe 10 microseconds rise time and 100 microseconds decay. They have major high frequency components. A low pass filter can provide minor attenuation but MOVs provide the real protection.

bud--
.

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