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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