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In alt.tv.tech.hdtv bud-- wrote:
| wrote:
| In alt.engineering.electrical Timothy Daniels wrote:
|
| | As always, "w_tom" ignores that the high voltages that short out
| | "3 miles of sky" will short out the underground power lines which
| | enter my building and buildings all over America. Anything able to
| | leap "3 miles of sky" will leap the fraction of an inch between the
| | power lines and the earthed metal conduit. What is left will be a
| | much lower voltage spike that can be handled by the average
| | "plug-in protector".
|
| It does not always make the 2nd leap to ground. There is not always a metal
| conduit available. I've seen such strikes.
|
|
| With no service panel suppressor it is well accepted that at about 6kV
| there will be arc-over from bus to enclosure for (US) circuit breaker
| panels. While arcing, the voltage will be hundreds of volts. Since the
| panel/system ground is connected to the earth electrode (US) most of
| surge energy is dumped to earth.

But what is remaining, in a significant surge, is still capable of causing
damage. A surge already has some high frequency energy. That moves on past
the point of arc even before the arc happens. Once the arc is established,
it can then produce its own high frequency effects. Ignoring this leaves
you open to more damage.

| If talking about a plug-in suppressor, Experiments by Martzloff (the
| idiot/member-of-the-IEEE) show surprisingly little energy reaches the
| suppressor. Circuit impedance greatly limits the current, and thus
| energy. Surprisingly, there is more energy at the MOV for lower surge
| currents (on short branch circuits) because the MOV can hold the panel
| voltage below the 6kV breakover voltage. With up to 10kA surges, the max
| energy at the MOV was 34J with most cases below 1.2J.

I've seen surge energy reach an appliance that is significant enough to cause
complete melt through of AWG #8 copper conductors. There was no protection
installed in that particular case.

--
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