Re: surge protection built into ordinary household electronics


"D from BC" <myrealaddress@xxxxxxxxx> wrote in message
news:4n9j635c248ggglgosln66k1q1t2r03e7q@xxxxxxxxxx
On Fri, 08 Jun 2007 09:39:24 -0700, mpm <mpmillard@xxxxxxx> wrote:

On Jun 8, 1:39?am, w_tom <w_t...@xxxxxxx> wrote:

What are you talking about??
I completely disagree with almost everything you say

Protection takes many forms:
- Fire Protection
- Physical Electrical Shock Hazard (Electrocution)
- Ground Fault Interruption
- Equipment Protection
- Component-Level Protection (ESD, etc..)

You speak of these as it they are all the same, or make inappropriate
comparisons.
THEY ARE NOT THE SAME!!!!

And the reason you don't see your phone or electric go down is because
they are REDUNDANT systems, not because they are immune to lightning!
(In the case of Electric, I mean the physical layout of the grid
itself. This is not always redundant depending on how your
neighborhood is served, and where the pole disconnects are located...)

I have seen cracked circuit boards caused by flying chucks of concrete
blocks walls that failed because of the percussive wave (Arc- Blast)
of lightning. Explain to me how a ground rod is going to help that?

As for your most egregious comment: That fuses are "not for
electronic protection", I suggest you take apart your TV set and put a
5,000 amp fuse in it. Then open the back cover and throw in about 2
pounds of glitter or aluminum foil. After the traces on the circuit
board lift (or melt) from the heat generated, you can explain to all
of us how fuses don't matter.

Regarding your "Earthing" comments, I don't even know where to
begin....
Please re-post your thoughts using the proper NEC Article-250
terminology. That would be a really good start.
As it stands, they seems to assume household-type knowledge of a
single ground rod driven according to local building codes. (Which,
as we know is a life-safety, fire-based code for clearing faults on
service entrances and branch circuits - not protecting anything
"electronic".)

When lighting strikes, there is a fault current flowing in the ground
circuit.
Do you really think that ground rod is doing anything for you at that
point?

I agree, you can make something nearly "lightning-proof", but it is
often economically or physicaly impractical to do so.
It is often cheaper to install redundancy, and this generally provides
other benefits besides up-time.

-mpm



I read that grounded post too..
It got me thinking though..

When lightning hits a power pole the energy is going to ground..
At the point of impact it branches like tree roots taking every little
indirect route to ground.
Most of the energy goes down the pole but some energy branches to
homes..
Let's say a home is lucky enough that that the spike voltage is below
the arcing voltage to earth grounded conduits and earthed "green"
wires.
What remains is a spike that could cause some damage..

Imagine connecting a 1 million volt AC supply to a house.. I think
there will be many arcing paths long before reaching a bedroom outlet.
Some years ago, I saw a person electrocuted in a factory, by a lightning
strike. He survived, but only with a lot of luck. What happened, was that
he was working on a lathe a few feet inside the factory building, which
was earthed to a very good earth point, near the side wall. Lightning
struck a tree, just outside the building only a few yards from the earth
point. The machine's 'earth', was suddenly massively elevated, relative to
the floor on which he was standing. It stopped his heart, but good medical
training from another staff member, saved him. Other effects, were to blow
apart some of the electrical conduits in the wall, and disintegrate quite
a few safety connections.
Where I worked at the time, we used to test electrical 'survivability' on
the kit we were making, to 250,000v, at 10,000A. for 1uSec, and then lower
currents and voltages for longer times. Every bit of our kit on this
particular site survived fine. However I have seen the same type of kit in
one case, literally having 'exploded', when installed on a site that
received a sequential multiple 'strike'. It is when you visit a building,
and see the remains of a 3/4 inch solid copper lightning conductor, that
has been vapourised, destroying parts of the brickwork behind, that you
beging to get an idea of just how powerful a really close strike can be.

Best Wishes


.

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