Lightning either struck my house, or very near my house, recently. This fried many of the electronics in the house, and even melted completely through the cord on a floor lamp! Here’s what mystifies me, though. No breakers tripped. My surge arrestors in the service panel did not trip. None of the outlet strips with surge suppressors tripped their breakers (I know that a $30 surge suppressor is no match for a direct lightning strike, but I would have at least expected them to give up their lives in a valiant, futile attempt to save my beloved electronics). How can there be enough current running through my house wiring that it melts a lamp cord, but none of the current limiting devices seem to have tripped, much less been effective?
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Lotta ways, some dependent on breaker mfg and type.
#1 is common to all breakers and is that the interrupt rating was exceeded by quite a bit and the contacts welded closed. Be sure to check that the breakers still open.
#2 is time delay, some breakers just plain are not fast enough, lots of specific techical reasons but breaker dependent.
#3 is that most of the current was in the neutral or ground leads, so didn't even go thru the breaker - look at your lamp cord and see which (or both?) side melted thru. You would be amazed at how circuitousy ground currents can divide and flow to get back to earth.
too many more to list, but the above is a start for you to consider, be sure to check your breakers to be sure they still work (short a romex together after everything is back to normal) and replace if they don't trip.
We don't get a lot of electrical storms, but when we do I go around and unplug stuff. Especially I unplug the computer from both the power and the phone lines, because that's a place where there's a potential path through an expensive box.
-- J.S.
Unplugging important things in a strong electrical storm is a very good idea.
You can certainly get surges in your house by electricity conducting through wires, plumbing, whatever...
Another thing that can happen in a very close lightning strike is electromagnetic convection. An electricity generator works by moving coils of wire (circuits) in a magnetic field. Usually this happens the other way around. What you require for convection to happen is relative movement between a circuit and a magnetic field.
The reverse happens as well. When electricity moves it creates a magnetic field. When lightning strikes a magnetic field opens up quickly (moves) and any ciruits nearby (microchips etc...) get a surge.
If they are not plugged in there are less opportunities for this to happen. Not likely a problem with far off lightning strikes. However the tree on your front lawn...Last year I didn't know what any of this stuff meant.
The lightning may have followed some other conductor (like plumbing) and then "bridged" across to the electrical circuit. Lightning can follow some strange paths.
But, that's a bit of a WAG.
The lightning strike is very brief. While the instantaneous amperage may be enormous, the "time average" current is much lower. Most breakers are designed to "average" current over several seconds (though with a sort of sliding scale, such that larger currents are averaged over shorter times). It's not at all surprising that a lightning surge would be too short to trip the breakers.
(Add to this the fact that it's CURRENT that trips the breakers, not voltage. Except for cases such as the lamp where there's some current-using device connected, the actual current in a circuit during a lightning strike may not be particularly high, especially when averaged over time.)
Re the surge suppressors, they may well have "given their all for the cause". The MOVs in a surge suppressor can tolerate a brief surge without damage, but will generally short out on longer surges. So there is usually a fuse in series with the MOV to disconnect it when it shorts. This fuse can be blown (or, in the rarer case, the MOV can be "failed open") without obvious signs of damage (other than the neon "protection" light, if any, going out).
You should replace all surge suppressors in the house.
Also remember that a surge suppressor is TOTALLY useless without a good ground. Make sure all the outlets you have "protected" equipment plugged into are REALLY grounded (consider installing new "home-run" circuits for high-value equipment) and not hot/neutral reversed, and make sure that the overall house grounding system is in good shape. Double-check that recent plumbing modifications haven't introduced a piece of plastic into copper water lines, install jumpers around water heater, water softener, water meter, etc. Make sure that there is at least one good ground rod (with good connection) in addition to the water pipe ground connection. If any reenforcing steel in basement walls, etc, is accessible, bond that to the ground system.
Also, add a grounding block at the entrance point for antenna and cable TV cables, running it to a good reliable ground.
Once, when Google-ing on lightning, I read that the grounding property of the ground under your feet varies from place to place, and that in some locales it is necessary to augment it. One suggestion was to bury a long piece of heavy chain in a deep trench for a ground.
I feel your pain. I lost two laptops to lightening this summer, and both were attached to an APC UPS. I'm just glad I don't actually own them. One is dead for good while the other has been repaired by Dell.
No breakers were tripped, and ONLY the computers were fried....not the answering machines, printers, or anything else connected to the same UPS. Bizaar.
Paula
Sorry to hear of your misfortune.
Breakers not tripping doesn't surprise me any. All the commonly used breakers are inverse-time breakers. The higher the overload the faster they trip. A common misconception is that when the rating shown of the breaker is reached current wise the breaker will immediately trip. Not so. It can carry the full rated load for several minutes. Any current from the strike passed through faster than the breaker could react.
That the surge arrestors didn't trip is not entirely surprising either. Metal-Oxide-Varisisters, MOV, are typically the initial, sometimes the only, barrier within surge arrestors. These are, for all practical purposes impossible to test for remaining capacity.
Most surge strips don't actually check the condition of the MOVs. They assume any large surge that destroys the MOVs when they have considerable reserve remaining would trigger a current surge high enough to trigger a tiny fuse within the surge strip. This blown fuse keeps the indicator LED off showing you the surge strip is effectively dead.
Sounds good unless you understand the MOVs are consumed a little bit by every surge they absorb. Some power surveys show that every day most homes get a few minor spikes, spikes that can reduce the longevity of delicate electronics, and every month there is likely one major surge. Even a near miss by lightning dwarfs both of these.
Because MOVs are consumed slightly in even tiny surges it is necessary to replace surge strips regularly. If a small surge destroys the MOV likely the tiny fuse will not blow and the Surge LED light will falsely tell you your protected.
How often you replace your surge strips depends on what your protecting, the quality of the surge unit you buy and your budget.
High value and critical electronics, like a computer that hold the information that you run a business out of or you high end home theater setups deserve better quality surge strips and more frequent replacement of it. A good quality init replaced every year is ideal.
When you replace surge strips don't throw them out. Demote them to other, less important, sensitive electronics. TV?VCR setup. The stereo system in the bedroom, the microwave in the kitchen and your kids PC are all go places. Try to establish a hierarchy and maintain that pattern. Once the surge unit has been moved a half-dozen times it can still be used as a power strip even though the surge capacity can be assumed to be essentially gone.
This has several advantages. The most important electronics get the best protection. The less important electronics get some protection and, because protection improves as more units are used in one house. You get better protection.
A whole house unit, installed in the main panel usually, can also help. These units are not sensitive enough to protect electronics but they are great for absorbing large surges and extending the life of the other, smaller and more sensitive, surge units. Because they are in the main panel they can keep most of a larger surge out of the house wiring letting through only what the other units can easily handle.
My theory is that the surge units you had were slowly degraded over time. Essentially they were useless but they had never seen a surge large enough, while the MOVs were still live, to blow the fuse to warn you the unit is no longer protecting your gear.
My advice would be, I base this on Florida where I am, would be to get a batch of surge suppression units. Expensive ones by well established for your high end electronics, cheaper units for the kids video game. Also I would install a whole house unit. Then keep up with demoting the surge units each year. Eventually the high end units will filter down to the kitchen microwave and radio in the garage.
I find it helpful to use a marker, silver sharpie on black units, to write the month and year the unit is first installed. This allows you to check and not just go on memory.
FS,
I've experienced 5 lighting strikes in my lifetime. Three at my current residence (we live on a hill with lots of trees).
IMO, lightning can take ANY path. Through plumbing, cable and telephone lines. From a tree and across a wet driveway through a steel post across the I-beam in your basement, then through the ground to your neighbors clothes line tied to a water pipe and down their well.
Forget about preconceived notions and theory of how electricity flows. The temps associated with it can ionize a path to anywhere, and vaporize "ground" wires.
WSJ
Very good point. The Lightning has jumped across a mile of open air. It will go just about anywhere it wants to go.
Also your point about protecting telephone and other lines is a good one. As I understand it more PCs are damaged through the telephone line than the power lines.
impossible to test for remaining capacity.
If you have a HV dc supply (a curve tracer is even better), you can check the leakage current around the knee of the curve. It helps to have measured it when new as the spec numbers can vary by an order of magnitude. If there is even one out of 10,000 homeowners who do this I'd be surprised, so your suggestions for labeling are really good. As you probably know, the MOVs fail due to more and more intergranular ZnO and other oxides interfaces getting slagged into an amorphous state with each surge, hence a higher leakage current. Tests I've done on MOVs show they usually dont fail open until a pulse 3X or more their single pulse rating.
Thanks for the information. I had realized there was some testing that could be done. I had understood it was less conclusive than some might want. A related story:
When MOVs started to be used in great numbers for important sites a program was tried by at least one company I have some dealings with. Theirs was dealing with RADAR towers and the MOVs they were using were the size of bricks and cost around $600 each.
Normal practice was that after a lightning strike or suspected damage the MOV sets were replace. The bean counters didn't like the idea of replacing expensive components without proof they were defective.
Sometimes this proof was easy. I have seen where a couple of MOVs virtually vaporized. It smoked the entire surge protection enclosure but it was easy to see where two of the MOVs had exploded. Everyone was amazed that these hefty units had disappeared leaving behind a black smudge and a remarkably small amount of material in the enclosure.
On the up side the surge suppression worked. It saved hundreds of thousands of dollars worth of equipment and everything worked once the suppression cabinet was replaced. More often it was an open question.
A plan was hatched by the bean counters to have the suspected units tested so any good ones could be reinstalled. A possible savings. Problem was, as the EEs put it, there was little confidence in the results and the handling and testing wasn't free. As they put it the only way to be absolutely sure of remaining capacity was to test them to destruction. This would eliminate any savings.
A few were reinstalled. In one case the lightning hit and destroyed $50,000 in electronics causing a loss of something like $250,000 in replacement costs and loss of service charges.
The EEs were brought in. Some of them said if new MOVs had been used the damage would have been limited to the suppression cabinet, a 2' square heavy metal of reinforced construction. A couple of others said it wouldn't have made any difference as it looked like a direct hit by the lightning. The later group said the only way to be sure was to reinstall new MOVs and have the lightning repeat the strike. As if the lightning would cooperate. All agreed new MOVs wouldn't have hurt.
In the end the bean counter lost. From then on if there was a question the MOVs, expensive though they are, were replaced and the old ones tossed, or held for temporary emergency replacements. They figured it was cheap, compared to the cost of equipment, insurance. As I understand it, it has been some time since I have had to deal with this, this is policy for a lot of companies.
I'm not an engineer. I do understand, in general terms, how these beasts work. Mostly I just do what the engineers say and follow the plans on commercial sites. They carry the certifications and high-dollar insurance coverage.
IMHO spending $50 or so to get a decent unit and moving the old ones to less important equipment is a reasonable plan likely to limit damage and increase the service life of those delicate electronics that, much like those MOVs, get worn down by the spikes.
Good story..
The attachment is of a big MOV prototype (installed 1000's of these in Minuteman sites on an upgrade in the 1980's, they were $500 apiece then. Have tested these to 300,000 amps for 10 millisecond pulses without losing protection (mov failed short, but 4/0 input wire fuses open at input terminal).
Neat photo. How thick is that beast?
The Lightning has jumped across a mile of open air. It will go just about anywhere it wants to go."
4Lorn,
Absolutely
And to repeat myself, a heavy metal [I] beam, post, or even a car chassis, can, and often does "redirect" the path of the flow of a strike.
Jon
Best course is, IMHO, is to provide a path you would prefer it to follow. Like most of us at some level lightning is lazy. It just wants to go home by the easiest path possible and have a nap.
Mostly. Sometimes even a system air terminals, a complete faraday cage and extensive ground plane get bypassed. Rare but it happens.
Some of those surge supressors have warrenties on them. On the box in the store they say things like "up to $25k replacement protection"... But I don't know what the warrenty really boils down to.
But you might check and see if your surge protectors had some kind of warrenty (or insurance) to cover the cost the stuff plugged into it that got zapped.