[NTLUG:Discuss] lightening!

[Darin W. Smith]

On Wed, 16 Jul 2003 23:25:35 -0500, <kbrannen at gte.net> wrote:
> Actually, about 10 minutes down the road in Argyle, there's a 
> store/service that sells them.  I have now considered paying them a visit 
> for information. :-)  My question is, if I install lightening rods on the 
> house, will that attract more lightening?
>
> I think I need to check out the UPS Chris mentioned too.
>

It's my understanding that if a lightning rod is properly bonded to an 
earth ground, it should actually work to discourage lightning from 
selecting your house, as opposed to say, a large tree nearby.

Basically, you want the house to appear at the same potential as the ground- 
-so that to the lightning, it appears that your house is just a flat piece 
of land.  To do that, the highest point needs to be at ground potential and 
the charge your house collects from the atmosphere must be continuously 
bled off to ground.  If you look at some of the really nice lighting rod 
installations, they usually will have multiple rods to create the field you 
would like, all bonded together by VERY heavy gauge copper cable...and 
multiple, bonded, grounding spikes (12 footers) driven into the ground.

On the other hand, the pointy nature of a lightning rod is meant to help 
persuade lightning that does strike to choose it as the path.  The point 
will tend to collect a charge (even being grounded) and will therefore 
produce a leader if the potential builds in that area.  Granted, the big 
charge produced going to the ground is also going to leak back into your 
house electronics--both through the neutral and the chassis ground wires 
which are both grounded nearby where the lightning rod will be (as well as 
telephone, TV cable, satellite, anything in the area).  In fact, any time 
there is lightning anywhere near you, you are getting small surges coming 
onto your power.  Those small surges, by the way, gradually make MOV-based 
(almost all "standard") surge protectors useless--the more surges they 
catch, the quicker the MOV is destroyed.

Technically, if you have an antenna of any sort, it is a lightning rod.  
The reason the NEC specifies that they must be grounded is because you want 
to bleed the charge they collect from the wind so you don't make them into 
such an attractive lightning target.  Plus the fact that your lead wire's 
shielding is almost certainly grounded to the building (chassis) ground--if 
not by a grounding block (where it should be), then by the equipment itself- 
-potentially creating an attractive target that is sure to kill any 
electronics on the other end of that wire.

Lightning rods and exterior grounding in general is meant to reduce the 
probability of catching a place on fire due to lightning strikes (by both 
discouraging the strikes to begin with and providing a safer and more 
direct path to ground for any strikes that occur).  You even see lightning 
rods sold to protect trees--personally, I'd rather it strike a tree than 
the house.  I'm personally very glad to have two very large trees in the 
front yard.  Lightning rods not really meant as a surge protection 
mechanism (AFAIK).

Panamax has a PDF file somewhere on their site where they describe a proper 
approach to surge protection involving both whole-house protection (these 
are actually relatively inexpensive devices) as well as individual device 
protection.  As soon as I can get a service upgrade and extra breaker box 
installed, I'm getting a whole-house unit.  There are some of those that 
also are supposed to help protect against lightning-induced surges on phone 
and cable lines.  As a simple precaution at my house, I have my cable 
running into a little cheapo radio-shack neon-lamp-based surge protector.  
Not ideal, but might keep my modem from getting slowly destroyed by the 
dozens of small surges we have around here in the spring and summer.

-- 
D!
Darin W. Smith
AIM: JediGrover
"If you pick up a starving dog and make him prosperous, he will not bite 
you. This is the principal difference between a dog and a man." --Mark 
Twain "Pudd'nhead Wilson's Calendar"