[TowerTalk] Fwd: Re: Re: lightening strike

[Bill Weinel]

Hi Skip,

Sorry to hear about your lightning incident. I had the same thing happen to me 
about 14 years back. Lightning hit a tree between my neighbors house and mine. 
The voltage surge produced was on the electrical, phone, and cable line and 
blew up all kinds of stuff.

After recovering from the damage, I found that the issue I had experienced was 
caused by improper ground bonding leading to differential ground voltage rises 
between separately grounded circuits in my house. (i.e.: the difference in 
voltage between two different ground points over a short period of time.) 

Theoretically, you'd think ground potential should be the same everywhere. 
This is not true, because a point current source in the ground at some 
distance between two separated ground points will cause a different voltage at 
each ground point caused by the resistance between the voltage source point 
and the ground point by Ohms law [E=IR]. (Unless the distances happen to be 
exactly the same, and the ground resistance is uniform, the voltage measured 
at each point will be different.)

Differential ground voltage rises are caused during a lightning strike by the 
surge arriving at two separately grounded circuits at slightly different times 
caused by the distance of each ground from the point source. This causes 
significant voltage differences (sometimes on the order of hundreds of volts) 
between the two circuit grounds for a number of milliseconds and thus causes 
damage to any loads connected between those circuits. 

In your case, differential ground voltage rises is likely what took out all 
your gear. 

If you do some research on the subject, you'll find that lightning prevention 
experts recommend that all grounds in a building be bonded together to a 
common ground point. This point should also be the entry point for all 
services coming into and out of the building. This is known as a single point 
ground. The purpose of this is to prevent differential ground voltage rises 
during nearby a lightning strike.

While almost impossible to do unless your dealing with new construction, the 
goal in an existing building is to minimize the ground resistance between 
separate circuit grounds by bonding them together with large gauge, low 
resistance conductors. This is typically either copper strap or large gauge 
copper conductors. This means interconnecting the electrical, cable, and phone 
grounds together to a single grounding point with a heavy gauge low resistance 
conductor.

By doing this you can minimize the effect of differential ground voltage issues 
during a lightning event.


73 Bill W4WHW



On Wednesday, July 10, 2013 12:28:13 PM Skip K3CC wrote:

> I have had one very bad lightening strike that I lost almost all
> the appliance's  connected to the electrical service.
> THey included, hot water heater, cook stove, freezer, dishwasher
> my entire radio station, computers , TV, Stereo ETC.  You get the picture.
> 
> The strike was a ground strike that came in through the ground system of the
> electrical panel and phone line.
> This strike took out 4 homes and all the under ground utilities had to be
> replaced.
> 
> I have never believed in any kind of lightening protection.  I used to live
> on top of a hill at 1200 ft.  I now live in a 20 acres field at 2300 ft. 
> How can you protect against a strike through the grounding system ????
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