Close lightning strike effects

Monday night, while working at my computer, a strong thunderstorm moved through this area, which is a very damp valley leading to the Loch Raven Watershed area in MD. Hearing several thunderclaps seconds after flashes, I considered shutting down my computer and disconnecting the power cord and phone line. A few seconds later, I saw a bright flash and an immediate loud "boom", and all power went out. I smelled something that could have been ozone or burnt phenolic. I set up emergency lighting, looked for any signs of fire, and took a brief look outside. Electrical power along the road up to the junction with a main three phase feeder was out, and both my phone lines were dead. Luckily my pets and I were not.

BGE arrived about 5 AM the next morning, determined that a fuse had blown, and power was soon restored. When it was light enough to see, I looked for other signs of damage outside. I have two houses separated by about 80 feet, and at the corner of the second house (used for storage) stands a huge Sycamore tree, probably 150 feet high. I found some wet, broken branches, and some pieces of bark, but no signs of major damage. However, I noticed that several panes of glass in a window just about two feet from the tree were broken, and two of them appeared to have blown outward. It looked like a raccoon may have jumped through the glass (which is possible, as I have found them in that house). Also near the tree is a 240 VAC twisted utility line, actually touching the tree at one point, and a drop cable to a meter box which is disconnected. I do have power to the house through a UF cable for convenience, fed from my residence on two 20 amp breakers. Also just below the power line is my active phone line, which connects to an interface box and then through a four wire line to my residence.

I discovered that one of the breakers had tripped, and I reset it with no problem. There was a second storm in the afternoon that caused loss of power again, but it was soon restored. The telephone technician found 48 VDC and a dial tone on one of the pairs, but not the other, and replaced a blown protector device which restored one line, but the other seemed to be an open circuit to the pole. An access box on the pole was open, possibly from the lightning strike or perhaps it was being repaired by another technician.

The damage to my equipment included a blown modem in my computer, damage to my computer speaker internal amplifier, and a damaged phone answering machine. I feel lucky.

I don't know the exact path of the lightning, but I think it may have hit the 15 kV (probably) main line and arced over to the transformer secondary and over to the tree, where it traveled down the ground paths. I think a direct hit to the tree would have caused more damage. I am curious about the pattern of the broken glass in the window, however. At first thought, I would expect lightning to ionize the air and create steam pressure from rain, so it would be an explosion with outward force. I think this caused some of the initial damage to the window, as evidenced by glass shards inside the house. But I think this may have been followed by a partial vaccuum that caused the sudden expulsion of higher pressure air in the house through the cracked glass. I will take pictures of it before I repair it.

It was almost prophetic that I was just reading some posts in SED referencing high voltage arcs and lightning, and also now reading the other post about conductivity of trees.

Now it's raining again, and I think I hear thunder.. AIEEE!

Paul

Reply to
Paul E. Schoen
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Are you sure the thunderstorm was working at your computer, or was it just looking at p*rn? ;-)

Reply to
John Popelish

Replace all of your surge protectors. They were wounded, saving the rest of your stuff. With good protection you should be able to survive a nasty strike but the protector is probably toast..

Reply to
gfretwell

"Paul E. Schoen" wrote in message news:44acae7d$0$12728$ snipped-for-privacy@news.coretel.net...

One thing you can do is to make sure you ground is actually grounded and not floating. I have grounded my wall outlet's ground to a 3 foot rebar outside the outlet because of a similar incident. You could probably also mechanically hook up a varistor between the ground and hot and another between the ground and neutral just incase. These things don't require much expertise although you would need to be careful when handling the mains(try and turn off the power if you don't know what your doing ;). It might not be the easiest method but it would probably be just as good as as a surge protector(as most are crap). You could even hook up a fuse and make a little custom box outside that houses these components incase you need to change them). Its probably cheaper then buying a decent surge protector and would work well. Ofcourse you could take it farther and add more protection if you have expensive equipement. Ofcourse this won't stop ESD from getting at your equipment but will stop voltage spikes from doing any damage(at the cost of a very cheap varistor). I'm sure someone else more experienced in this area and make a better suggestion though. Its really up to you... but if you can drill a hole, splice wires, drive a rod in the ground, and solder then you could set up a decent amount of protection for your wall outlet in less than an hr for just a few bucks. (although you could make it more elaborate too by adding more sophisticated circuits)

Reply to
Abstract Dissonance

The grounds in the electrical system are probably pretty good, as all of the wiring has been redone, but much of it is still temporary as I do major work on this house. There are actually two solid grounds on the incoming power, one to a water pipe and the other to a well-driven ground rod in moist earth. However, that one was disconnected when I was putting new siding on and it may not have been tightened up. The advice to replace the surge protectors is good. Now I have the computer on a UPS which is in turn connected to a surge protector. However, the best protection is physically unplugging the computer when storms are active.

I think the main surge came through the phone lines, as both of them were damaged. The one is not yet fixed, but the other (the one I use for the computer) had a blown protector, which essentially shorted to ground and opened the connection from the external line to the premises wiring. However, it was not enough to protect the internal modem, so I am using an old external unit.

An answering machine on the other line was damaged. The 9 VAC adapter showed an open circuit input, but the machine does not power up when a separate source is applied. I have a new one I hadn't yet installed. Time to do that. This indicates a power line surge, but with voltages and currents as high as lightning the path of the arc is unpredictable. I think the main ionizing blast was along the outside of the tree and to the power lines and phone lines outside the house next to it. Of course, some pretty hefty transients were likely conducted into other parts of the telephone lines and power circuits.

I think the computer speakers were damaged by the same power line surge that damaged the answering machine. They were also on an AC adapter, and the high voltage spike probably damaged the amplifier inside (it now runs hot). Possibly a DC output adapter would have limited the surge due to its internal capacitance. The computer power supply may have been spared because the input consists of inductors, diode bridge, and large capacitors, and the surge protector also limited what it saw.

Just tonight I managed to inflict my own damage, but I was a little bit lucky. I had a Microchip ICD2 (on a USB port) connected to a target board that was plugged into the AC line. I was measuring voltage on the board when my probe slipped, and it connected the circuit ground to a point that went to 120 VAC through an LED and optoisolator. Both of them instantly opened up, which probably limited the possible damage, but the ICD was hurt. I thought I may have damaged the USB port on the computer, but it worked with another device. Luckily the fault occurred to ground, but apparently the ground of the ICD was not as solid. It seems like an internal regulator in the ICD is getting hot, so it may be repairable. Luckily it is only about $150 for a new one, but now I will need to wait until it is repaired or replaced, and I need it for working on this new SCR board design. Maybe I'll power it from a separate 12 VDC source while I am doing the development work.

Thanks for the ideas. Maybe the safest method is to run the computer off a battery and an inverter, and possibly rig up a fiber optic phone line for internet access. I can keep the battery charged up with a generator on an exercise bike, and not be connected to the power grid at all!

Paul (reposted via Google - lost by Coretel)

Reply to
Paul

Water pipe ground typically is not sufficient for transient protection - often too far away. It's not just earthing that is important. Distance to earthing and how that connection is routed are also essential. Earthing for household transient protection typically means a connection should be less than 10 feet. Other factors such as no sharp bends, not inside metallic conduit, no splices, and separated from other non-earthing wires also apply.

Typically phone lines are not struck being below AC electric. And destructive surges don't just enter on one wire, damage, and stop. First the transient forms a complete electrical path from cloud to earth. Then electricity flow through everything in that path. Finally something in that path fails. Most often, telephone appliances that connect to both AC electric are damaged by transients incoming on AC electric.

A most typical path is incoming on AC electric, through answering machine, and then outgoing to earth ground via telephone line. Those phone line protectors may have failed because a larger AC electric transient found earth ground via answering machine, computers, or portable phone base station. Other damaged electronics (speakers) were also powered from AC; not connected to phone line. Without a well earthed 'whole house' protector, then virtually everything inside the building was exposed to incoming surge. Things damaged must also complete an outgoing circuit to earth - ie telephone line appliances.

Your post implies insufficient earthing (path to earth ground either too long or maybe not common to all utilities). Also demonstrates how telephone appliances are so often damaged - incoming on AC electric and outgoing through the telco's 'whole house' protector.

Earthing means every incoming utility wire in every cable (overhead or underground) must make a short (low impedance) connection to the same earth ground before entering a building. Coax cable needs only a ground block and short hardwire connection to earth. Phones have a 'whole house' protector provided by the telco. AC electric is the most common incoming path for surges; needs a 'whole house' protector.

Your post is typical of a surge > The grounds in the electrical system are probably pretty good, as all

Reply to
w_tom

On a very near by strike, I lost 2 Ethernet cards, a wireless router (AC adaptor still works good), a DSL modem, and a wireless USB mouse receiver. The phones, TV gear, VCR, stereo's (some were on), clock radio's, etc were all fine. I think what had happened was that the 100 - 150 feet of Ethernet cable acted as a large antenna / air core transformer.

A similar thing happened about 10 years ago where a large arc came out of our wood boiler controller, when a close by strike occurred. The boiler has a ~35 foot length from the floor to the tip of the stainless steel chimney. The only grounds on the system are from the 120V AC feeding the system, and the copper water lines, which are only grounded by the pump switch and the water, which has to go through 50 feet of plastic tube to get to the bottom of the well.

Reply to
Jeff L

More likely is it was the path that reconciled a ground shift. We ended up fixing problems like that with a fat bonding wire (PC case to PC case) between machines that were far apart or on different A/C circuits and adding ferrite beads to the LAN.

Reply to
gfretwell

Possible, but the bolt hit the ground (close to the driveway), and there was no other damage to any other equipment in the house other then listed. The AV gear (TV's, cable boxes, VCR's, etc) were fine, even though they are on separate circuits and connected with a common cable, but the cable is grounded where it enters the house. The computers were otherwise fine, The Computers are basically right above each other, one on the main floor and one on the second. Power comes from the panel in the basement, also in that same corner of the house, but are on separate circuits. The telephones were fine and most have wall warts for power, like the DSL modem so I doubt that the telco and power lines had much of a voltage differential during the strike. The USB wireless mouse receiver was totally enclosed in plastic, sitting on a wooden desk, and that was completely dead.

That should add a bit of protection! I once installed a short optical link (RS 232 IIRC) for eliminating a ground loop in an industrial app, that it would be ideal for this type of isolation. Someone must make Ethernet optical isolators, then again maybe not since Ethernet (not PoE) uses isolation transformers on each end, and fiber could be used in apps that required more.

Reply to
Jeff L
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I took some pictures of the effects of this lightning strike. I looked closely at the power line, and saw that the neutral (steel support cable) around which are wrapped the two 120/240VAC feeders, was vaporized open in the vicinity of the big sycamore tree. The window near this was broken along the path of the arc which I think continued along the side of the tree down to the ground, where it also got into the phone lines. I think the first strike may have been on the incoming power lines, even though they are disconnected at the meter. They are actually touching the tree, and that is where the neutral was damaged. I called BGE and they will be removing these power lines.

There are four pictures (about 300 kb total) on

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My personal phone service (through MCI) is still out, but by business service was fixed by Verizon within 24 hours. Apparently business customers get top priority. The estimate on the MCI repair was 1 week. They have two more days. I wonder if I can prorate my payment for phone service to deduct for a week without the service?

BTW, I saw on the news that someone was struck by lightning while listening to an iPod while mowing the lawn in a thunderstorm, and they warned against use of iPods and cell phones during electrical storms. I really don't think there is enough metal and electrical field with such devices to attract lightning. A steel mower with a high voltage spark plug is a more likely culprit. Any thoughts?

Paul

Reply to
Paul E. Schoen

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