[geeks] Whee! Lightning strikes, AGAIN!

[wa2egp at att.net]

> You original post didn't make it clear what you were saying.

Sorry if I was not clear.

> It doesn't really matter, because you are still wrong.

Whatever.

> In fact, the OP is a little bit wrong too, but not near as much.
>
> For one thing, you guys are talking about two different things:
>
> 	1) lightning rods
> 	2) lightning dissipators
>
> You are talking about a lightning dissipator.  They are ungrounded,
> pointed rods in most cases, but some designs are spiky or even
> blunted.  The theory is that they will bleed off charge and reduce the
> potential difference between ground and cloud.
>
> The lightning research community generally rejects the idea and
> further says that it increases strike probability rather than reduce it.

>From what I've read, "they" are not too sure either.

> There *IS* current when you use one, but it isn't enough to complete
> the ionization path, and it results in a larger electrical field and
> heavily ionized (conductive) air rather than a reduction.
>
> Most of what is sold out there is pseudo-scientific crap.
>
> A lightning rod is, by contrast, designed to intercept a strike and
> direct it to a controlled ground.  The theory here is to channel it
> through a safe path to prevent it from channeling where it will do
> harm.  All lightning rods are grounded to earth or water, sometimes
> via a grounding network or a building frame designed for that purpose.
> Some earth grounds used are salted underground cable networks.
>
> The lightning rod creates a field above the rod which intercepts
> nearby strikes by acting as an upward streamer channel which connects
> with cloud->ground stepped leader and connects that to a controlled
> ground.  This helps prevent the strike from going through structure,
> people, electronics, etc.
>
> NOTES:
>
> Regarding sharp points.  New research indicates that round or blunt
> points produce better intercept performance, and in the US all new
> lightning rods are round or blunt.

Gee, Maybe the sharp points dissipate the charge.

> Ben Franlkin did originally claim rods were dissipators, but he later
> retracted after he realized that they needed to be fully grounded, and
> that they attracted, or intercepted strikes.  However, he never did
> fully understand the mechanics of it, ionization, leaders, etc.  He
> ended by saying "it is somewhat of a mystery".

I read where he did not connect the wire on his first one to ground but had it
dangling in his chimney (I guess so he could do other experiments) and touched
it when a storm was nearing.
I guess after he picked himself up, he decided to connect it to ground. :-]
>
> > Oh yes it is designed to prevent strikes.
>
> No, they aren't.  They are strike interceptors.
>
> Lightning dissipators are designed to prevent or reduce strikes, but
> don't appear to work.

I haven't seen any research saying either way but it would be interesting to
find out.  Can you cite any?

> > And if it supposed to be struck by lightning then why to they put
> > them on buildings with metal frames and no ground wires to the
> > lightning rod.
>
> They don't.  If there is no rod->ground connection, then it is not a
> lightning rod.  See above.

Oh yes they do.  I know of several buildings where this is done.  Of course
this could be contractors not installing things correctly.  I live in Jersey,
get it.

> >  If the frame takes the lightning strike, then why use lightning
> > rods at all?
>
> To intercept the strike and bring it to a controlled ground.

I know of some buildings with metal frames and metal roofs and still have
them.  Darn contractors again. :-]

> > A good place to see where they are positioned is in Florida.  They
> > have them all over the place at Sea World.
>
> I'm sure if you ask someone who knows, you'll find they are grounded,
> they are lightning rods.

Find someone who knows.  Hmmmmm.  IIRC they are grounded and pointed tips.

Actually there is a picture in a edition of a Haliday, Resnick and Walker
college physics book that shows a girl on a metal lookout platform (taken by
her boyfriend) with the typical hair all spread out from static charge.  The
text below the picture states that after the picture was taken, the couple
left and five minutes later lightning struck the platform.  Deaths resulted
(other tourists).  Now that would be a place to test lightning
rods/dissipators.
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