Lightning

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Dauninge

Well-known member
Joined
Jul 18, 2014
Posts
70
Location
Oklahoma
So last nite the 5th wheel about 50 ft to my left caught on fire and burned to the ground. No one was hurt thankfully. It was storming pretty bad and though no one knows for sure yet, the owners think it might have been a lightening strike.

My question: On the back of my MH, I have about a 20 ft pipe attached to the back ladder, then on top of that I have about a 4 ft section of PVC with my cellular antenna on top. The pipe is NOT on the ground. It is about 2 ft off the ground secured to the ladder. The cable runs from the antenna on top into my rear bay attaching to the "outside" cable connection, then the coax that runs through the coach to the inside amplifier/booster and internal antenna.

Total height above the MH is about 15 ft, so roughly 27 ft in the air. There are much taller trees around me. Should I take the pole down? Is it a lighting strike potential?
 
That's a good question, we have a wifi extender and put it down when there is bad weather but now I am wondering the same!  It is attached to the ladder though.  Be interested to see what folks think.
 
The neighbors had about the same length pole, except all metal with a plastic TV antenna on top. Theirs was attached to their ladder as well, but it went all the way down to the ground, whereas mine didn't.

It's still storming here so I went ahead and took it down anyways. Only took me about 10 minutes. (Wasn't lightening when I did it.)

I am still curious though as to whether it would have been "safe" to leave it.
 
The path lightning might take is a very difficult thing to predict.  Lightning rods on structures do work to some degree, but still not 100%.  Many times, it appears that lightning did not take the path of least resistance, but often the path of least resistance is created by lightning itself as it ionizes the air.

A home I once owned was a concrete block structure with stucco veneer.  It had a masonry fireplace chimney that stood about 3 feet above the ridge of the roof.  Approx. 10 feet away I had a TV antenna mast strapped to the corner of the house and stuck into the ground, extending several feet higher than the chimney.  About 15 feet away from the house were three 30 ft + tall Chinese Elms in line, much taller than the chimney.  During a lightning storm, we took a lightning strike.  It didn't strike a tree.  It didn't strike the TV mast.  It didn't even hit the highest point of the chimney.  Instead, it hit where the chimney joined with the edge of the roof, 3 ft below the highest point of the chimney.

[font=verdana, arial, helvetica, sans-serif]So, your mast may be a potential strike point, but I doubt lightning is that discriminatory.[/font]
 
I guess I'd unhook the cable in wicked storms.  I've always felt anything conductive (cable), is a source for lightening to travel down.  Sometimes just wet things are enough to pass electricity
 
Two stories that come together to make a point....

Lightning will travel down even small wires if it gets to them.  Back in the mid 90's I saw a presentation by Bruce Fisher, a guy that had worked as a scientist of some sort with NASA doing lightning research...flying a F-106 into storms directed by ground radar trying to get struck.
https://www.f-106deltadart.com/nasa_lightning_research.htm

In his slide show, I remember a photo he had of a small GA aircraft, I forget if it was a cessna or piper maybe.... anyway the lightning had entered a wing tip and traveled down the nav light wiring that was just inside of the leading edge, all the way across to the opposite wing tip where it exited out the other nav light.
Now, remember the magnetism that comes with electricity flowing through a wire?
remember the right hand rule?
Well that magnetism completely imploded the leading edge of that wing.  Instead of the nice rounded "nose" it was completely inverted into a cup shape.
the plan made a safe landing...hence the photograph of it!

second story.... when I was a teenager, my dad and I were in his boat fishing off shore.  It was a small flying bridge boat with a cabin so we were inside shelter.  Lightning struck.....flashbang....I felt a zing, and everything shut down.  Now power, no starting the engine, no lights....nothing.  But no apparent damage so we figured it hit the water nearby? 
So we threw out the anchor and resumed fishing once the rain passed.  later a big charter headboat came by and towed us in.  Once back at the dock, someone pointed out the top of the CB radio antenna was black.  Actually it was the top of the lower segment.  The top half was gone!  So what happened was lightning hit that antenna, and through that wire got into everything that was turned on.  Anything that was switched off was fine.  Anything on was melted.  The windshield wiper that was on...melted.  the one that was off, ok.  every light bulb, electronic ignition module, etc... that was on...melted.  Literally goo.

Anyway, My point is this.  If lightning does hit that antenna, it will almost certainly get into your RV and will likely travel all around through it.  I'd suggest grounding that antenna.
 
Grounding an antenna isn't as simple as it sounds, and is probably more dangerous if not done properly. I've spent several hundred dollars to make sure my home amateur radio antennas are properly grounded and bonded.

If you're really concerned about lightning, dropping the antenna is a better choice.
 
I took it down. I wasn't prepared to take the risk. There was no way it was properly grounded, if at all. (It was not touching the ground and no additional ground wire connected.) It's not going back up either. At least not in that configuration.

It was amazing how fast that RV burned to nothing. Less than 45 minutes and it was gone. I'm really glad that they made it out OK and that my MH didn't go with it. Most important is that everyone is OK.

I thank everyone for the replies.
 
johnhicks said:
Ground the metal pole to a four-foot ground spike or take it down.

Grounding in such a manner is not appropriate, for many reasons. Without getting into a prolonged technical discussion on grounding and bonding (of which many can easily be found on electrical and communications forums), just don't do it.
 
First. when it comes to lightening you have two things that damage. a DIRECT HIT and a NEAR MISS  I've had the "pleasure" of both. A Strike abut 200 yards from where I was parked (Thankfully I am somewhat protected so that only damaged some MOV's slightly) and a Direct on a Radio Tower I was using (Professionally) Believe it or not the tower survived save for a converter (Just like in your RV) that was the only thing totaled

Grounding the mast will help. Code is a 10 foot pipe but 10 one foot tent stakes is good too and a whole lot easier to insert and remove.. Use heavy wire.. I use 10 ga but you really should use heavier. and no kinks  gentle sweeping curves yes. kinks no.
 
Guys, please stop with the bad advice.

The NEC is very clear on this topic, along with recognized industry standards for lightning protection.

Both suggestions posted are incorrect in that they promote isolated grounds, which can be lethal to humans and equipment.
 
OK, enlighten us please.  If you were to be using such an antenna, how would you do it?
I'm guessing your an amateur radio operator.  Do you ever set up a rig while RVing?  How do you ground it?

Of course pulling it down is the "easy answer".... and that works maybe a bit better for something of occasional use.  For checking messages once a day....check the wx, put up the antenna, do your business, and pull it down.
but for something like TV or cell phone, that may be used more frequently, used into the evening, etc... pulling it down every time aint so practical.  Especially considering storms might sneak up on you when you are away.... or while sleeping

So I figure an antenna that's up is of course going to be a likely point for lightning to strike.
if it does strike, lightning WILL travel down the wire.
It's either going to travel all through the RV, OR try to jump out to ground if that's more direct and easier.... actually I'd imagine that most of the energy would jump regardless.... it's probably only a partial of the strike that would travel through a small wire...but still....
having the wire grounded through a coax ground block, like you'd use for a sticks and bricks application makes sense to me....
sure having it grounded to the electrical grid's ground  or a proper ground array makes sense
but isn't it better than the alternative to give a more likely place for the energy to jump ship...such as grounding the cable to the mast which at least gives it a direct path to earth, even if that contact is only the mast touching the ground....or the mast within say an inch of the ground?  Seems to me that this would be an easier and more direct  path than it networking through the chassis and all that wiring to find a way out past the tires or through the shore power cable...
 
I think I am just going to mount the antenna itself to the ladder using the 4 ft PVC that I have. I don't need to have it so high up in the air. That way I can take it down quickly if needed. If I were going to use the previous setup, with the metal pipe, I would run a ground wire as John advised. I would run a ground from the mast as well as a ground from the ground coax connector at the RV both to a proper ground pole. (Well, as proper as I would be able to in the RV Park)

I realized as the dog and I were in the car a safe distance away, that I really need to think about being able to break camp in a timely fashion. I have double slides and an extend-a-stay hooked up.
I wouldn't move the MH at all with the slides extended. I figure best case scenario I could have had the MH ready to move in minimum 20 minutes, most likely 30.

It would have been too late by then. Within 10 minutes of the fire starting the flames were already raging and embers dancing through the air. The fire dept. arrived in just under 20 minutes. (They are a volunteer FD, so considering they had to get out of bed at 11:40 at night, get dressed, drive to the FD, suit up and drive here, I thought that was pretty good time.) My MH is fully insured, so I just grabbed the dog and my phone, jumped in the car, and got a safe distance away. Made sure the neighbors had made it out and dialed 911 on the way out.


 
blw2 said:
OK, enlighten us please.  If you were to be using such an antenna, how would you do it?
I'm guessing your an amateur radio operator.  Do you ever set up a rig while RVing?  How do you ground it?

While I don?t attempt to comply with NEC 810 and Motorola R56, I do try to comply with the best practices of the standards. I carry a grounding kit with some #6 and #12 wire, a ground buss bar and assorted clamps, which all fit into a canvas bag. I bring this same stuff to Field Day.

The radio and coax shields get connected to the bus bar, then I go looking for a ground. One can be usually found at the pedestal, a cable TV connection or occasionally a copper water pipe on the site.

If severe weather is forecast, I?ll disconnect the antennas and pull the coax out of the RV. I?ve also been known to drop the antennas and disconnect from the power pedestal if things look really bad. For the most part though, I don?t worry much about lightning.
 
When we installed solid state FM broadcast transmitters, the manufacturer had several recommendations on how to minimize lightning damage to the equipment above and beyond the NEC requirements.

First is to provide a direct, straight path for lightning to go from the tower to ground.  Lightning prefers to travel in a straight line, so if there's a direct path to ground it will prefer to take that route.  If you're going to have a ground rod, put it directly under the antenna, not on the other side of the RV.

Next make it harder for the lightning to travel into the building or RV.  Make the coax exit the tower at a right angle then pass it through a ferrite choke.  If the coax is flexible enough, wrap it in a loop so it passes through the ferrite twice.  This won't eliminate the lightning getting in, but it will slow it down a bunch.

If you don't have ferrite chokes, loop the incoming coax several times to form a coil.  This will also encourage the lightning to take the straight path to ground instead of through the equipment.

Finally, minimize ground paths across the building.  By this I mean having the tower and coax enter on one side and have the power line ground on the other side.  Voltage coming down the antenna line will enter the building on the antenna side, then travel across to the power line ground on the opposite side.  If the tower coax and the electrical entry are on the same side and ideally connected to a single grounding point less voltage will flow across the room and anything that's in it.

If you're interested, here are couple of brief articles showing how it's done in professional installations:

http://www.radioworld.com/tech-and-gear/0003/field-service-tips-grounding/340684

http://www.tvtechnology.com/opinions/0004/power-surges--part-two/276965
 
Way back when, 1969-1974, I worked as a Class B operator on a line crew. When we set poles a copper wire was run down from the top which was connected to a lightening arrester. A lightning rod was pounded into the ground next to the pole. I think they were ten foot sections and we used maybe 2 or3 sections.
 
blw2 said:
Two stories that come together to make a point....

Lightning will travel down even small wires if it gets to them.  Back in the mid 90's I saw a presentation by Bruce Fisher, a guy that had worked as a scientist of some sort with NASA doing lightning research...flying a F-106 into storms directed by ground radar trying to get struck.
https://www.f-106deltadart.com/nasa_lightning_research.htm

In his slide show, I remember a photo he had of a small GA aircraft, I forget if it was a cessna or piper maybe.... anyway the lightning had entered a wing tip and traveled down the nav light wiring that was just inside of the leading edge, all the way across to the opposite wing tip where it exited out the other nav light.
Now, remember the magnetism that comes with electricity flowing through a wire?
remember the right hand rule?
Well that magnetism completely imploded the leading edge of that wing.  Instead of the nice rounded "nose" it was completely inverted into a cup shape.
the plan made a safe landing...hence the photograph of it!

second story.... when I was a teenager, my dad and I were in his boat fishing off shore.  It was a small flying bridge boat with a cabin so we were inside shelter.  Lightning struck.....flashbang....I felt a zing, and everything shut down.  Now power, no starting the engine, no lights....nothing.  But no apparent damage so we figured it hit the water nearby? 
So we threw out the anchor and resumed fishing once the rain passed.  later a big charter headboat came by and towed us in.  Once back at the dock, someone pointed out the top of the CB radio antenna was black.  Actually it was the top of the lower segment.  The top half was gone!  So what happened was lightning hit that antenna, and through that wire got into everything that was turned on.  Anything that was switched off was fine.  Anything on was melted.  The windshield wiper that was on...melted.  the one that was off, ok.  every light bulb, electronic ignition module, etc... that was on...melted.  Literally goo.

Anyway, My point is this.  If lightning does hit that antenna, it will almost certainly get into your RV and will likely travel all around through it.  I'd suggest grounding that antenna.

Lightning sure does weird things; Once our dryer quit heating. I pulled it out to check it and found a lightning strike going from the dryer to the washer. No idea where it came in the house but the dryer element was fried.
 
When I worked in the A/C repair and Appliance business, I saw where a strike hit a tree a few feet from a house corner, jumped to a condensing unit cracking the concrete and moving the unit 8", moving somehow across the house jumping off a turn-off vlv under a commode, blew a 2" hole in the floor, and jump off a 1/4" water line to the refrigerator on the other side of the house. I think it ignored all other paths to grounded stuff. Found this to be a good link to monitor when having antennas up. http://en.blitzortung.org/live_dynamic_maps.php
 
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