Re: Why no TV?

Seth Breidbart <sethb@xxxxxxxxx> wrote:
> Keith F. Lynch <kfl@xxxxxxxxxxxxxx> wrote:
>> Unfortunately, reasonable amounts of insulation make no difference
>> to lightning. It's already punched its way through a couple miles
>> of thin air,

> Typically, rather moist air to begin with,

I said "thin air," not "dry air." It actually doesn't make that
much difference. Moist air is a better conductor at less than its
breakdown voltage (due to two ten-millionths of all water molecules
being ionized at room temperature), but that has little to do with
what the breakdown voltage is.

Besides, if the temperature of the raindrops is less than the dew
point, the rain will actually make the air *drier*.

> and ionized air for the main current flow.

It's only ionized because the voltage per meter exceeded the air's
breakdown voltage. That's what it *means* for a current to punch its
way through an insulator.

>> after all, and few insulators are much more than ten times better
>> than air.

> But lots aren't subject to the same sorts of ionization when hit by
> a large voltage.

On the contrary, that's the only way significant current ever gets
through any insulator. The voltage exceeds the insulator's breakdown
voltage, a path through the insulator becomes ionized, and those ions
move in response to the voltage, constituting a current. The only
difference from air is that the breakdown voltage is ususally higher,
though not orders of magnitude higher, and the breakdown damage is
usually permanent: A capacitor that shorts out is an ex-capacitor.

If rubber is a ten times better insulator than air, then a lightning
bolt that can punch through 2000 meters of air can punch through 200
meters of rubber. So rubber-soled shoes and a rubber hat are utterly
worthless as lightning protection.
--
Keith F. Lynch - http://keithlynch.net/
Please see http://keithlynch.net/email.html before emailing me.
.

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