[ale] there's Risk and there's Stupid

[Dan Lambert]

The primary rule I was taught about lightening protection was that the
BEST method of grounding was to have a single grounding point for all of
the grounds in the facility (home, business, or whatever). It may
require three or more ground rods all interconnected to create an
adequate earthing, but all of them should be connected to the equipment
at one point. The Service entrance ground is generally recognized to be
the primary grounding electrode.

The reason for this is that the EMP that occurs when a lightening strike
occurs, propagates through the ground as a wave like a ripple in water.
If the equipment is connected to two independent grounds, there will be
a potential voltage differential between the grounds as the pulse
passes, and if the equipment is connected to two separate grounds, it
becomes part of a current carrying circuit. It will not survive.

This has worked for me in every case except one strike. That one hit a
tree about 15 feet from the service entrance. 

Dan


On Mon, 2009-04-20 at 14:05 -0400, Robert Reese~ wrote:

> > Question:
> >
> > We now live in a condo development and all the utilities are
> > buried, specifically, phone, power, and cable. The nearest
> > overhead, exposed utility line is more than 100 meters away. Does
> > this fact in any meaningful way lessen my risk of having a large
> > surge take out unprotected electronics (tvs, tuners, etc.) and
> > protected ones for that matter?
> 
> Yes, quite.  Both power plants and lightning seek ground.  The cables in the 
> ground, while capable of accepting and even attracting lightning strikes, are 
> encased in a pseudo-Faraday cage.  That doesn't mean you are completely 
> protected, but it does mean the risk is much smaller.  (Ironically, the 
> insulation protecting the cables from the earth also inhibits the protection 
> that the earth would help provide by keeping it away from grounding and 
> directing energy up the line in both directions.)
> 
> 
> > I know that really LARGE surges can
> > blow right past a good UPC/ surge protector.
> 
> Surge protectors, even those supposedly designed to "prevent lightning", cannot 
> do so from a direct strike.  Lightning travels frequently miles through the 
> atmosphere; a small "spark-gap" present in many consumer surge protectors won't 
> stop that surge.  Better ones do have capacitors and other forms of capacitance 
> to help relieve larger surges, but again nothing to completely stop lightning at 
> close strike ranges.
> 
> I recommend a battery backup which will do a far better job at protecting your 
> equipment than any consumer-grade surge protection system of which I am aware.  
> You get the added benefit of power-loss protection for things such as your DVR, 
> your DVD, 
> 
> Note that these only address power, and sometimes phone line.  As far as cable 
> goes, do yourself a favor and sink a 10' copper ground rod in all the way next 
> to your cable box and attach your cable's ground connection to that rod.  They 
> aren't expensive and can be purchased at your local big box hardware store along 
> with the heaviest gauge solid wire you can find; you won't need much, perhaps a 
> couple of feet.  As a bonus, you can also attach your telephone ground there as 
> well as add additional grounding to your plumbing (if it is metal-based, that 
> is).
> 
> Cheers,
> Robert~
> 
> 
> 
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