Grounding for lightning strike

[kb0zke]

From another thread: "Ever think of a lightening strike and your rig not being grounded?"


Consider that a lightning bolt has millions of volts in it and travels quite a few miles. An Airstream, car, or truck has a metal body, yes, but they also have rubber tires filled with air. Those tires might be a bit of an insulator for even 120 VAC, but are nothing to a lightning bolt. The Airstream has a tongue jack and stabilizers. Even with a nonconducting pad between the stabilizer or jack and the ground, that little bit of insulation isn't going to matter. As far as the lightning bolt is concerned, the car, truck, or Airstream is close enough to the earth to provide a path.


If you are boondocking out in the middle of nowhere you could run a length of welding cable or other large conductor from the trailer to a ground rod that you have pounded into the ground. That would probably protect your tires from being blown out. On the other hand, if there are some tall trees in the general area you are probably safe from a lightning strike, as the tree will be the target. Remember, tallest thing = target.


If you are in a campground and you don't have a good surge protector, you might want to consider unplugging the electrical and cable/satellite and stowing the cords. More than a few people have upgraded the television, refrigerator, microwave, stereo, etc. because of a high voltage spike. Just don't wait until the lighting is so close you can't count between seeing the flash and hearing the thunder.

[Mollysdad]

There's something known as the "skin effect". basically it claims that when hit by lightning, the charge stays on the outside of the vessel. That's why you're safer in a car.
I spent a lot of years boating in Florida, and tried to avoid lighting, but you can't always. I recall one particular event where I rediscovered religion, and I'm not embarrassed to say so. We were maybe 10 miles offshore, and in terrible weather (The forecast was good). Bad enough that I motored west to avoid hitting something, and a small bird landed in the cockpit, thinking we were a better choice than being tossed in the storm any more.
I'm soaking wet, I'm holding a steel wheel, and looking up at my 50' aluminum mast, while lighting is hitting the water in front and behind me. I prayed.
I did not get hit. My boat manufacturer didn't believe in grounding. They believed, rightly so, that grounding increases your chances of being hit. It provides a better path from your mast to the water.
I then researched lightning, and was surprised to learn it starts with a flow from the Earth to the cloud. Called a streamer. The bolt then follows that path back to the ground. It's big, maybe 400,000 amps! I always used a fiberglas antenna, and many people installed a "ion dissipator" which looked like a steel broom upside down on the top of the mast. The theory was it dissipated the ions before they became a streamer. Make sense?
Or it was the prayer.
When the storm passed, the bird took off.
Anyway, we pulled into Saratota for the night, opened a bottle of wine and said, "It wasn't that bad!"

[Warpath]

Unless you live in Hill valley. Then you can expect 1.21 Jigawatts to send you back in time.

[Boxite]

A sailboat (or any boat but a sailboat with a mast in particular) on the water, or under a lone tree or under a cliff-edge/over-hang is the WORST place to be.... immediately after a metal roof with metal rain-gutter/down-spouts.

Moral: You do NOT want to “ground” your Airstream. Your AS an your car are the safest places to be because they are like a “Faraday Cage” and will protect you. It’s why airplanes (and passengers) do not suffer serious damage despite being struck by lightning in-flight.

[quietguy]

Originally Posted by Boxite

A sailboat (or any boat but a sailboat with a mast in particular) on the water, or under a lone tree or under a cliff-edge/over-hang is the WORST place to be.... immediately after a metal roof with metal rain-gutter/down-spouts.

Moral: You do NOT want to “ground” your Airstream. Your AS an your car are the safest places to be because they are like a “Faraday Cage” and will protect you. It’s why airplanes (and passengers) do not suffer serious damage despite being struck by lightning in-flight.

Yes. Please google Faraday Cage and under no circumstance ground your airstream or truck to the Earth. Stay safely inside your rig, hopefully not parked under any solitary large trees and don’t touch the skin of your airstream during an active lightning storm. You’ll be fine. If otherwise was “a thing” there’d be mention of it in your owner’s manual for liability reasons!

Happy Fourth! Be safe. Wear your mask. Social distance and wash you hands! Tell someone important to you that you love them!

[JCWDCW]

You can and do want to ground your AS if you want to avoid a lightning strike.

Misconception is that the grounding is to carry the charge from a lightning strike.
The witches broom, and any lightning rod for that matter does not attract the lightning. The sharp point bleeds off the accumulated charge so that the charge in the clouds is not attracted to your position. The reason people on a golf course get hit is they are the highest point on flat ground and the charge on the ground is just screaming to get off the high point (person). As noted when the charge is great enough, a leader jumps to the clouds and the massive electrical capacitor discharges through that leader to ground The sharp point of a lightning rod behaves like a capacitor shorted to ground. The charge is suppressed (bled away) and never really gets too high at that location. The mast on the boat is grounded to the metal keel, or a metal plate attached to the hull under the water line. The bleed off of the charge protects anything or person inside the "cone of protection" which is a circular space inside a 60 degree cone around the mast.
So if you want to protect your AS then a #8 or#6 braided wire attached to the AS frame or skin and to a decent ground rod driven into the ground deep enough to be in moist soil will do the trick. (no you don't need #2 wire...you can't put any wire big enough to carry a lightning strike...you want to bleed off the charge.) Then you need to provide the point to bleed off the charge on the skin...make up something pointy to attach to the trailer when a storm is brewing???? A good set of alligator clips and the wiring and accessories can be stored in the bumper compartment till needed.

JCW

[JohnTF]

Lightning is unpredictable , even the organizations that study lightning state this , it's probability phenomena .

I am a full timer and a ham also , this story in only a data point
I had 3 vertical antennas , 2 HF over 30' high the 3rd a UHF / VHF 20' , the masts they were on were grounded , the coax at the base of each mast was grounded .
The trailer was using the " factory " ground lug next to the water inlet .
The shore power power in the camp grounds was as should be .
Then lightning hit a tree 30-40' away , the branch it hit was huge oak tree and came down on a brand new Jeep & motor home , the power panel - the parks power panel was wiped out .
My trailer was 20' from the power panel , and my hookup was 3' away and only had about 4' feet of cable out , the ground wire of the factory cord melted all the way into the 1st junction box , not the breaker - breaker box is at eye level , the junction box was under the bed .
This is where the melting stopped ----- and no damage to trailer , anything in the trailer or any ham gear , including the antennas .
This park was crowded with mostly very old oak trees .
My theory was that the grounding and all the metal I had in the air - antennas , did the same thing in the post with the boat , I have see and read a lot on the lightning stuff , including the defusers shown above .

[guskmg]

I know of an incident where a bass boat driver, on the water was hit and killed. The lightening went through him, steering system, down the engine to the water. His passenger was also killed. They were found just floating up against the shore. On another, a glider pilot flying a carbon fiber constructed glider, was it on his head and the lightening traveled through his body to the metal ruder pedals then out the rear of the glider. I had strikes hit my aircraft and not know it until the post flight inspection. Do all the above to stay safe.
guskmg

[Wabbiteer]

Streamers - think ten thousand points of static all competing to solve a shortest path / highest potential equasion, whole herds of those things in sizes from fractions of an inch to dozens of feet long until just one wins and the loosers flink backwards into non-existance...

- I've sat next to one and had enough time to wonder what that noise is, a hissing/buzzing and glanced to look square at it, it was like something living and clawing into the air to get released... then everything turned white. Some other streamer won but not before the modems and phones in the house surrendered to the force, while seated at my desk in front of a window I'd seen the phone wiring hissing toward the aluminum siding!

So anyhow - there are ten-thousand wannabe points of lightning and any one of them can or will mess things up.

Once a strike is happening (elsewhere) one of the old phone linemans tricks is to loosely coil the bell wire just around an empty air space, the timing electricity takes to spin circles of little 3-inch circuit paths will likely see the event over with before damaging currents get past the coils. Putting ferrites on power feed conductors, even one twist through a ferrite 'ring' might do the same thing, just delay a build-up long enough so more* of the event plays out elsewhere. That can be done with feeds into trailers too.

I just remembered, when looking at high-voltage circuit boards in consumer devices they often have rows of sharks-teeth conductors that run parallel to each other, these nearly touch so if an arc is going to have its way anyhow the engineers choose where it will happen - that is another passive trick, before the mains wiring goes spider-web they have that final point where the shortest path to earthground is provided with just the thickness of hot/neutral wires insulation away - so, if invaders are running fast into our system 'gates' then the jump to the most appealing ground happens at that choke point and not across circuit breaks/fuses/switches blah blah...

And last - don't linger at the door, either in or out - no holding grab bar standing in dirt and looking over your shoulder to try and see what that funny noise is...

[mikeoxlong]

Lightning is a very interesting topic.
In my professional opinion (and I’m sure someone will disagree, because someone always does) the only useful purpose of a ground rod is to channel lightning to the earth. Is it useful on a trailer? Possibly...I lean towards yes.
More useful would be adding a lightning arrester to your electrical panel.

[Davidwantz]

Reading this thread, I am reminded that Mark Twain had an opinion about lightning rods as well.

Read his essay Political Economy. It's not about politics at all, but about a guy trying to write about economics and is pestered by a lightning rod salesman.

Very funny read.

[overlander63]

We were in our Airstream when it was struck by lightning. Other than a damaged shore power wire and a scorched-looking mark on the roof near the TV antenna, there was no damage to the trailer. I do remember needing to change my underwear, though--but that's another topic.

[bweybright]

So I am really confused by those saying to ground your trailer, others say no?. Part of my confusion is the ground rod (2) they pounded into the ground for my shop floor were 6 feet long....so I should do this every time I camp? I am wondering because if I can't ground it properly then what should I be doing?
Please professional and amateur electronic professionals chime in to help me out to figure this whole grounding thing out.

I would ask that you state your qualifications relating to this question with your response so we stupid lay people can ascertain your knowledge versus opinion response. Thank you.

[overlander63]

https://vehq.com/rv-lightning/

[ROBERT CROSS]

Faraday cage....👍


Bob
🇺🇸

[Justinfinity]

As a lifetime boater and an Airstream owner, the only protection you have against a lightning strike is luck and a good insurance policy. Don’t even entertain the notion that you can control or mitigate that kind of force. There are plenty of people happy to take your money and give you bad advice and ineffective gadgets.

[HiHoAgRV]

I have always viewed this subject as 2x parts. Avoiding getting struck and surviving getting struck. As far as once struck, well, all bets are off.



As far as not getting struck, lightning is trying to find the easiest path between ground and the sky. That is why we have all been told to not be under a tree (it's tall and full of water, shortening the path and increasing the chance that lightening will jump there) and we all know to not fly kites with metal keys in a storm.



By using the same analogy, adding a better, shorter path between the ground and sky is bad, right? By tying a 10' tall metal object (Airstream) to a ground rod simply increases the chance of getting struck as I see it.



Lightening doesn't necessarily 'strike' and airliner, is is simply using the airliner as a high conductive shortcut to it's ultimate path.



I guess I will start ground my camper when they add grounding rods to airliners... ;0)

[JCWDCW]

Originally Posted by HiHoAgRV

I have always viewed this subject as 2x parts. Avoiding getting struck and surviving getting struck. As far as once struck, well, all bets are off.
As far as not getting struck, lightning is trying to find the easiest path between ground and the sky. That is why we have all been told to not be under a tree (it's tall and full of water, shortening the path and increasing the chance that lightening will jump there) and we all know to not fly kites with metal keys in a storm.
By using the same analogy, adding a better, shorter path between the ground and sky is bad, right? By tying a 10' tall metal object (Airstream) to a ground rod simply increases the chance of getting struck as I see it.
Lightening doesn't necessarily 'strike' and airliner, is is simply using the airliner as a high conductive shortcut to it's ultimate path.
I guess I will start ground my camper when they add grounding rods to airliners... ;0)

SO a tree in the middle of nowhere is the high point at which the accumulated charge on the ground accumulates. It is eventually the greatest concentration of electrical charge and will eventually send out the leader to the clouds and the resulting discharge of electricity (lightning) from the cloud will follow the leader back to the tree.
A lightning rod bleeds off the charge slowly so there is no build up of static. A lightning rod is a 'point' that is an easy escape for static electricity. If you are the only object in the field in an Airstream you will be the high point at which the charge accumulates as being the closest approach to the opposite charge in the clouds... ground rod or not
So you have two choices ...don't be the only one in the field, or ground and install something pointy on your roof. A lightning rod reduces the chance of a strike, it does not improve the chance of a strike. I f you don't believe me go ask the designers of tall buildings why they put multiple rods on the highest point. The tie in to the ground from those rods is only a 000 wire; about 1/2 inch dia. It will never be able to carry the millions of amps coming from a lightning strike. It's rated fro 200 amps.

Earlier question about the length of a ground rod.
The 6 ft ground rod was for grounding an electrical short in the 120V system and needs to be deep in the ground to ensure the short will flow to ground. Not the same grounding as for lightning. A lightning rod in a temporary situation may only need to be in moist soil to ensure there is a conductive path from the pointy thing on the roof to the ground.. When we measure resistance for static electrical bonding in industry we only need less than a million ohms. When we ground for electrical short we need less than 25 ohms.
I'm putting this out there from industrial experience and design. Personally I won't be living in an AS that is parked out in the middle of a field. I can't be bothered to go though all the work to protect it.

JCW

[BayouBiker]

The Dissipation Theory, the idea that lightning rods prevent or significantly reduce the chance of a strike in any particular area, has largely been discredited in extensive studies over the past 30 years as the mechanics of lightning has become better understood. It has been repeatedly shown the number of rods in any particular area need to number in the thousands to make any statistically significant difference in strike probability. On the other hand one rod above an otherwise featureless area, will significantly increase the chance the rod and anything it is attached to will be hit if the step leader (a negatively charged step leader from the cloud initiates the lightning strike, not the streamer) ionizing a purplish zigzag pathway toward the ground prior to the uprising positive Streamer. With a grounded pointed rod, the likelihood the streamer initiates at the rod when the step leader is perhaps 150 or so yards above and within a 45 degree angle cone upward from the rod is nearly 100%, at 30 degrees it drops to about 50%. Without the rod, the streamer has a reasonable chance of initiating from a nearby discontinuity like a bush, mound or tree.

So do not add a rod in hopes it will prevent a strike, it won't. Instead find a spot with some features 25-100 yards away. Don't park too close to a single or spaced out trees, the lightning will find the aluminum a better conductor than the tree trunk.

[mikeoxlong]

Another misunderstanding.
The standard 10’ ground rod does not direct a short in your home 120/240 volt electrical system to earth. Electricity seeks the path of least resistance back to its source. In your home that would be the transformer that feeds your electrical panel.