Things that go BOOM during the daytime...
In October 2010, I had a direct lightning strike on my HF doublet antenna, which was suspended about 70 feet over my house, between two tall trees.
I was at home at the time, working in my home office in the basement, next to the ham shack. There was a tremendous BOOM! and the room I was in -- which has no windows -- lit up as bright as day.
I knew something bad had happened, because many of my computer UPS power supplies were beeping, and there was that bad, burnt electronics smell in the air. The dogs were going wild, and my internet connection to work dropped.
Remains of 450 ohm window line
After I made sure wife + dogs + house were OK, nobody hurt, no fire, I
started to survey the damage. First I went out in the back yard to look
at the antennas.|
The 450 ohm feedline from my 135' doublet was destroyed, only bits of plastic were left lying all over the roof and back yard. What pieces of this I collected had no metal in them at all, just a little bit of coppery color on the outside of the plastic ribbon.
There was a huge scorch mark on the back of the house where the feedline was held off by 18" pvc pipe standoffs.
The doublet feedline fed int a 4:1 balun, which was grounded to a 8' ground
rod right at the entry to the house. Also grounded to this ground rod was a
lighting arrestor the coax feeder from a Diamond VHF/UHF "white stick" antenna.
The lightning was not much interested in this grounding system. It came down
the 450 ohm feeder, past the DC ground at the balun, and into the lightning
arrestor for the white stick antenna. It continued into the house on the
VHF/UHF feeder and down into a test repeater I was running on the bench.
Later inspection of this coax showed a series of holes blown through it where
some of the lightning energy found its way to the metal suspended ceiling grid.
The repeater radio and duplexer survived the strike. The Astron linear power supply powering it was blown up, and the prototype repeater controller was completely destroyed.
The lightning apparently exited the repeater controller through a CAT-5 ethernet cable connected to it, and got into my wired network, destroying a 24-port ethernet switch, router, the cable modem, and my Elecraft K3 HF rig.
The lightning also found its way out of the Astron power supply, through the AC cord, and then out through the bottom of a Tripp-Lite surge suppressor lying on a metal rail underneath my hamshack desk. There were some pencil eraser sized burn spots on the surge suppressor and desk rail. I think this is what blew up the K3. My logging computer was also destroyed, but I that may have gotten in through the wired ethernet.
A few other things were destroyed or damaged beyond repair from this strike, including parts to my telephone switch, a garage door opener, a stereo receiver, game console, some LED night lights, and a variety of other computing gear connected to wired ethernet in my home.
In all, this one lightning strike did close to $6000 damage. I was very lucky that my house did not catch fire and burn to the ground. My homeowners insurance took care of all but $1000, but it was not fun to get the settlement done.
Some of the victims
I did not want this happening again. A whole lot of analysis was not necessary, as it was pretty clear to me that the lightning did not find my single ground rod where my antenna feedlines entered the house to be as low impedance to earth as the electrical power system in the house, and Cobb EMC's (the local power company) grounding. The lightning energy came in on the antenna grounds, made its merry way through ethernet, telephone, power, and other wiring, and finally found ground through the electrical wiring coming into my house from the street, but not before wreaking havoc on a lot of my expensive technology.
I needed to create a single point ground system for all the wiring entering my home.
I did some reading on this, including a study of the relevant parts of the National Electric Code. As I understand this (and I am a software engineer, not an electrical engineer) outside antennas must have a lightning arrestor at the entry to the structure, and the lightning arrestor must be electrically bonded to the building ground, grounded water pipe, the electrical service entry, or electrical service equipment. You can read the NEC yourself online, the relevant parts are in "Article 810". You can legally access the NEC at https://law.resource.org/pub/us/code/states/ga_electric.pdf
My goal was in keeping the lightning out of my home, so bringing the ground wire for the lightning arrestors into the house to bond to a water pipe or the electrical service equipment inside the house did not seem like a particularly good idea. I decided to bond my antenna lightning arrestors to the power entrance at the electric meter.
This presented it's own set of challenges, because the meter was about 15 feet away from the best spot to bring the feedlines into the shack, and 15+ feet of ground bond wire also did not seem to be a good idea, either...
What I decided to do was to install 5 new ground rods, all bonded together with #2 solid copper wire. These are arranged so one is directly under the power meter, then spaced 5' along the perimeter of that end of my house. The 4th ground rod is right under the antenna lightning arrestor ground bus, and there is one more ground rod 5 feet past that one.
I called Dig-Safe to have the underground utilities marked before I started driving ground rods. I did not want to drive a ground rod into the underground electrical or gas service to my house.
I dug a trench to install the #2 ground wire about a foot below ground level. I dug bigger holes at the location of each ground rod, so I would have room to drive the top of the rods below surface level.
At each ground rod, I used a CadWeld OneShot exothermic weld to permanently bond the #2 wires to the ground rod. The pictures below show the welding of one ground rod: this is #2 solid copper wire (almost as big as a pencil) to 8' Erico ground rods.
The Cadweld mold, ready for the shot
Exothermic welding. This is in broad daylight!
After the weld. You can see the blue igniter box here.
The new ground tied into the power meter
|I hired an electrician to bond the power meter to my new grounding system. I was quite surprised to discover that there was no ground wire at my power meter at all! There was only the wiring that came underground from the street, and the wiring that went into the house to the electrical service panel. (The electrical service panel is grounded to a copper cold water pipe, but the I later discovered that the copper does not go far into the earth before it changes to PVC and goes to the street. Really not a good ground at all.)|
|Outside, at the point where the antenna feedlines enter the house, I installed a copper bus bar and three PolyPhaser lightning arrestors. The copper bus bar is bonded to the fourth ground rod in the string with #2 solid copper wire. I also fashioned an entrance to the house for the feeders from a 90-degree "sweep" section of electrical conduit.||
Lightning Arrestors where feeders enter the house
Inside the shack disconnect
|Inside the house, I made it much easier to disconnect the antenna feedlines from the radios. I installed six SO-239 barrel connectors onto a piece of angle aluminum bracket. The bracket is connected to the ground wire from outside, and the antennas are all attached to these connectors. I bought some "push-on" PL-259 adapters from The Wireman, and the radios all connect through those. This makes is fast and easy to connect and disconnect the radios from the outside antennas. I also used a huge knife switch to let me "float" my station ground when I am not operating. With the AC line unplugged, and no more ethernet wires to the shack computer, my station is completely "air-gapped" when I am not using it.|
I also bonded the cable TV and telephone my my new ground system. I bought a gas-discharge lightning arrestor made for cable television and installed that on the cable TV wire, outside the house. That arrestor is grounded with a # 6 wire to the #2 wire to my new grounds at the power meter. I moved the ground wire on the telephone entrance box from the Rube Goldberg arrangement the phone company installed (25 feet long!) and grounded that directly to my new ground system. I also installed a "whole house surge suppressor" on my electrical service panel.
In order to mitigate the risk of the long runs of ethernet (Cat-5) wiring, I converted a lot of the technology in my home that was using wired ethernet to wireless, including my ham shack logging computer. Pretty much all of the computers that are not on the same branch circuit as the cable modem, router, and ethernet switch is on wireless now.
I cannot prove that any of this is working, but two weeks after I finished the bulk of the work, in July 2011, a tall poplar tree in my front yard received a direct lightning strike. Only one piece of electronics in my house was damaged, a television media player box that was connected (still! duh) to wired ethernet at the very closest point in my house to the tree that was struck.
I still disconnect and unplug all the radio gear when I am not using it, but I will also point out that when the first strike occurred, my K3 got zapped even though the antenna was not connected -- I think it got it either through the metal desk or through the computer interface cables.
To summarize: read the NEC and understand how your antenna feedlines should be protected where they enter your home. Bond all grounds together outside your house. The electrical service, cable TV, telephone grounds should all be common, but on my house, this was seriously mickey-moused. Install lightning arrestors on all your antenna feedlines before they enter your house. Bond your radio lightning arrestors to the same grounding system as everything else. You want to make these grounds have the lowest impedance to "earth" as you possibly can. The goal here is to give lightning with a better way to find earth, rather than by going inside your home and through your equipment.
Oh yeah... unplug everything before storms are expected.