[cctalk] Re: EMP was: oscilloscopes

On Apr 2, 2024, at 1:30 PM, Jay Jaeger via cctalk <cctalk(a)classiccmp.org> wrote: Paul, would you mind if I shared this on the Facebook EndFed Halfwave Antenna group? Time and time again I see folks talk about putting in ground rods in for antennas and NOT bonding them to the electrical service ground rod. In most (if not all) locations in the US, this kind of bonding is now a required part of the electrical code, and newly constructed houses (or ones that have their panels replaced) will typically have a "service ground' bus bar installed near the electrical panel. (The ARRL book is a pretty good resource on this topic, too, but real life experience may convince some to think twice about what they are doing.) https://www.arrl.org/grounding-and-bonding-for-the-amateur JRJ On 4/2/2024 10:13 AM, Paul Koning via cctalk wrote: > >> On Apr 2, 2024, at 11:01 AM, Jon Elson via cctalk <cctalk(a)classiccmp.org> wrote: >> >> On 4/2/24 00:03, Just Kant via cctalk wrote: >>> Accordimg to certain individuals on this list, going back a few years, electronics/computers can be damaged due to an electrical storm, presumably very intense activity, even while off. Go look through the archives. >>> >> I have had two incidents where nearby lightning strikes blew out components on gear I had. Many years ago, I had two computers connected by a parallel port cable, and chips on both ends were popped by a strike that might have hit power lines about two blocks away. >> >> About a decade ago, we had a lightning strike that hit trees half a block away. It took out an ethernet port on one computer, and blew out a bunch of stuff on a burglar alarm I had built. Both involved long wire runs. > Some years ago we had a lightning strike on the driveway next to the house. It took out every single device directly or indirectly connected to the cable TV (also Internet) connection. The reason was something I knew about but which I did not sufficiently understand: the cable TV connection came into the house at the opposite end from power and telephone, and was grounded there. > > A lightning strike will set up a voltage gradient in the soil near the strike, so the "ground" seen by power and phone was at a very different voltage than the "ground" seen by the ground rod "protecting" the cable TV entry. The resulting current actually evaporated the cable TV surge protector innards, and took out TV, printer, cable modem, Ethernet switch, PC, and a bunch of other things. > > Lesson learned: I rerouted the cable TV to go first to the power entry point, and attached its protector to the same copper ground sheet that the other two protectors sit on. > > A great reference for all this is the handbook "The grounds for lightning protection" by Polyphase Co., a maker of professional lightning protection devices. I haven't done everything they call for -- for example, our house doesn't have a perimeter ground. But it does now have single point grounding, and as a result we've had no trouble even though there have been plenty of lightning strikes in the neighborhood. > > paul >