Posted 16 July 2014 - 01:03 PM
Well Sunday of this week we had some real storms roll in with lots of lightening. Nothing hit but there was a lot of activity. Monday rolls around and it's around noon and we can just see thunderheads building up to the east. I was inside and my son was out in my garage working in the office located out there. It was getting dark but still actually quite light outside. The rain was just a drizzle when out of absolutely no where BAM! a bolt came down and hit one of the rods on the garage. The sound was deafening and the light overwhelming. The bolt must have split also as a neighbor with a metal airplane hanger and horse barn very close by reported a hit also. For me, since I had protection, there was no damage to the building or electronics what so ever. I do have a CAT5 cable buried between the structures (the garage is a separate building) and the port on my 16 port switch that connects the garage to the house did pop. All of the other ports are actually fine but that one port blew. Had I installed the grounded ethernet surge protector that my contractor gave me out there for specifically that reason I probably would not have had that problem either. It was actually on my "To Do" list for this week. It will definitely get done now.
Being that my residence is located in a rural location, all of our heating is propane. My home was built using black pipe for all of the internal propane feeds but my garage/studio was constructed using flexible gas pipe. That pipe is fine and meets code but it does not have the current handling capability of black pipe. As such there have been instances where, when a strike occurs in the wrong place and the current travels across one of these flexible pipes, they heat up enough to melt with the resulting propane explosion. Not good. My contractor made sure that all of my gas lines are bypassed with grounding conductors to prevent this kind of catastrophe.
The few curious things about this strike was that there was absolutely no warnings. We could see a storm coming but until our strike there had been no thunder. Second, if I had to judge we were not "in the thick of the storm". If anything we were right on the leading edge of the approach of the storm when it hit. Had you asked me 1 minute before the strike if it was safe to go outside I never would have given it a second thought. While I did not see it specifically, I do know we were hit. The doorway right under where the rod is located smelled of burnt electronics/ozone for a good 10 minutes. At first my son and I were concerned that there was a fire in the attic but we checked and all was fine. Other than the blown port there was no damage to anything that I have been able to find. Our neighbor was not so lucky. Their security camera was blown as was a lot of the outlets in the stable. They are very fortunate that a fire did not start as the stable was occupied by two of their horses and of course there is lots of hay inside. The poor animals must have been scared out of their wits.
A last curiosity. I had been leaving the dome electronics on while I'm up here, even in daytime. In a static mode it does not take that much power and one less thing to turn on at night. Well I won't be doing that anymore. After the storm passed I went out to check on things. The main PC for some reason was locked up but after a reboot was fine. The curious thing was my dome was happily spinning around, and around, and around and around....... and had been doing so since the strike had hit. It is a TI dome and I'm using the TI dome controller. Again, after a reboot all was fine but had I not been here I would most likely have burned out the motors. "Won't do that again" as they say.
Posted 16 July 2014 - 01:35 PM
Over the years I've found it a good idea to physically unplug anything that isn't being used at that moment, since as you've experienced, lightning doesn't always knock before entering. It's a pain, but not so much as replacing electronics would be.
Posted 16 July 2014 - 01:36 PM
Posted 16 July 2014 - 10:13 PM
Posted 16 July 2014 - 11:58 PM
Posted 17 July 2014 - 12:11 AM
When designing the grounding system for observatories, I use the Motorola R56 standard specification for communication sites. It has very comprehensive chapters on grounding for lightning protection and grounding for communications.
Posted 17 July 2014 - 12:23 AM
Posted 17 July 2014 - 02:59 AM
I have a small counterpoise style grounding field with 4 interconnected grounding rods and a large copper plate suspended from the wall of my battery shed on ceramic insulators as a single point ground. Also multi stage surge protectors on the phone-DSL line, solar panels, 110V, etc.
Notice the copper plate, single point ground, on the wall to the left in the attached image. Notice the surge protectors on the electrical panel to the right. There is a set of ear protection on one of the surge protectors, no pun intended.
Like most others I have a lot of sensitive equipment. Mine is nearly 4 hours drive from home, so no running around unplugging things. I can and have during close monsoons shut everything down. I have phone activated relays. The published strike probability for my site is 0.1/year/KM, this is low. As we all know it only takes is one nearby strike to be set back years and a lot of $$$. This near miss seems a good opportunity to learn more from other astronomers. Someone surviving a direct strike seems worth study, I think its a combination of good practices and luck... Thanks again for the reference! Best regards, Dave
Posted 17 July 2014 - 07:58 AM
Posted 17 July 2014 - 08:18 AM
I think that there is a LOT of miss-information when it comes to lightening protection as well as probably a lot of sub-standard installations. A bad or improper installation is the same as not having one at all. Contrary to some beliefs, lightening protection does not increase your odds on getting a hit, it simply protects you as best as possible if/when you do get hit. That being said, it is still a bit of a *BLEEP* shoot. No one can guarantee that there will be zero loss or damage. You can't predict lightening, you can only mitigate against it. One has to decide if the cost is justified. I certainly believe, in my case, it was more than justified. My son was in that building when it was hit. Actually sitting almost below the strike and right below a ceiling mounted propane heater. Had I not had that protection things could have been extremely bad, to the extent that I really don't want to think about it.
I had 3 structures protected. There are about 10 rods on my garage/studio, around the same number on the house and one on a large 30' custom tower that my son constructed for my observatory. Total cost from my contractor was just over $8K. The contractor I used has been in business a long time and has done numerous commercial and residential installations. (The picture of the tower next to the observatory on the residential page is my observatory). As in most things each person has to judge the risk/reward for themselves.
A few things of note to. I'm an electrical engineer and as such liked to think I knew about what was required before the contractor came out. After spending about 10 minutes with him going over what was needed, it became quite clear to me, I did not have a clue. There are a LOT of i's to be dotted and t's to be crossed to do a job like this properly. Now in 20/20 hindsight what was done is quite clear and makes sense but if you want to do it yourself I would thoroughly research the subject and/or hire an experienced licensed contractor to do the job correctly.
Like I said, I will post some pictures later today.
Posted 17 July 2014 - 08:48 AM
Posted 17 July 2014 - 08:59 AM
Lightening can strike 21 miles away from the storm. Very little warning.
I'd always heard that but now seeing is certainly believing. Quite scary actually.
Posted 17 July 2014 - 09:48 AM
Posted 17 July 2014 - 11:25 AM
"The vertical extent of a CG lightning channel averages 3-4 miles (5-6.5 km) with a maximum height of about 6 miles (9.6 km). Most CG flashes originate in thunderstorms between 15,000-25,000 feet (4,500-7,600 m) above ground level in the mixed water and ice region. The record horizontal distance of a cloud flash is 118 miles (190 km) that occurred in the Dallas-Ft. Worth area."
Posted 17 July 2014 - 12:38 PM
These are the rods on the house. As you can see these are spaced at about every 12'. This alone is what dispells the rumor that rods attract more hits. These rods are designed such that they protect a sphere with a radius of approx 6' - 8'. Outside of that radius the protection falls off rapidly, thus the need for multiple rods across a roof line.
This shows the rods on the studio/garage. If you look close you can see the aluminum cable that ties the rods together going down the right side of the roof line. I believe the rod either on the far right or one of the rods on the heater exhaust vent tubes just to the left was where the hit took place. As you can see, no visible damage and close inspection would show no discoloration.
Here is my observatory with the associated tower. The rod is on the north side. You can't see from this image but looking north there are very large ponderosa's so having the tower there really does not interfere with my observing as I can't see much in that direction anyway without doing major tree surgery, which I do not wish to do.
Here are some images of the feeders that go to ground. One image has a ruler in the photograph to give scale. That cable is 1/2" diameter aluminum stranded cable. They all go to 1.5'x1.5' copper plates buried about a foot down in the ground. The observatory not only has a plate but there is a 1/2" copper cable buried about 8" down all around the building structure.
The image below also shows one of the many industrial surge protectors that are on each electrical box. (the small black box under the power panel)
Surge protector on observatory power panel
Here are images of the shunts placed on the gas lines
These are pictures of the Ethernet and RG6 satellite feed protectors
I have two 8 port switches in the observatory. Each one has these types of protectors. This is what I neglected to attach in my garage (on the to do list...... too late) and what most likely caused the port to pop on the 16 port switch in my house.
Posted 17 July 2014 - 12:58 PM
Posted 18 July 2014 - 08:54 PM
Walking, walking, walking, Snap, BANG. Lightening struck the utility pole about 40 ft behind us. Dog was home in seconds! It was the one and only bolt that day. A few seconds earlier and who knows.
Also had a strike on the neighbors tree, about 70 ft from my frt door. I only lost the modem on the PC. Everything was shutdown at the time as I was looking out the window at the rain and light show. In the morning, we found pieces of the tree blasted into the ground a few inches deep! The tree was totally severed about half way up and there was lumber all over the yard.
Posted 19 July 2014 - 08:30 PM
Posted 22 July 2014 - 05:21 PM
I do take exception to one comment in the second document:
"Lightning behavior is arbitrary, capricious, random and stochastic."
It is obvious to me that each and every lightning strike always follows the laws of physics.
Therefore the correct statement should have read "Lightning behavior is dynamic, complicated and can difficult to predict."
I was part of a team that designed, built and maintained communications facilities on mountain tops in Alaska. We built everything to the signal and lightning grounding recommendations in the Motorola R56 design specification document. Every year those sites absorbed literally thousands of direct lightning hits with very-few, if any, lightning-related outages.
I hope this helps.
Posted 22 July 2014 - 10:20 PM
Every year those sites absorbed literally thousands of direct lightning hits with very-few, if any, lightning-related outages.
Had I not missed two things, neglecting to put one of my two alarm systems on a UPS and the Ethernet surge protector in my garage, I do not believe I would have sustained any damage. Both of these errors have been corrected so hopefully, when Murphy decides to strike again, their will not be any damage.
Posted 23 July 2014 - 08:07 AM
Posted 23 July 2014 - 12:18 PM
Thanks to everyone for the good discussion here. It has caused me to decide to protect my new observatory from an adjacent ground strike by installing a whole-house electrical surge protector as well as ethernet surge protectors. Your expertise here may very well save my electronics some day.
Don't forget lightning-protection grounding and shielding.
Surge protectors aren't enough.
Posted 23 July 2014 - 12:24 PM
(One other thing I need to do is replace the cross-bracing wire cables with high-strength monofilament.)