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

[Scott Castaline]

Dan Lambert wrote:
> 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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Of course if you are able to, just shut everything down and pull the 
plug. I have everything on UPSs and large surge protectors, so I only 
have 3 plugs to pull along with the cable feed to my cable modem and tvs.