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bigeasy63 · 06-13-2007, 09:56 PM

As much as I have read the forums I have not yet seen this discussed, so I am hoping it is not a concern.
My wife and I were standing on our porch as a thunder storm with lots of lightning approached. She said " I guess the camper would not be a safe place during a lightning storm."
That prompted me to think about the aluminum construction and its vulnerability (for lack of a better word) to a lightning strike. I have learned in many classes in my job that inside your car is a very safe place to be because the car would ground a lightning strike. (The same would apply to a loose powerline. Stay in the car!) But would it apply to the airstream?
Does anyone have any advise on this topic? Or, even better, an actual experiance with this type of event.

Trying to keep this from being me...

Thanks ahead...

Janets Husband · 06-13-2007, 10:35 PM

I have never heard of anyone being hurt due to a lightning strike in a trailer.
Lightning has the attribute of traveling the path of least resistance, which means it would travel over the skin then jump to ground at the point of least resistance (It would be like being in a Faraday Cage). If you were not connected to shore power it should jump to ground probably at the banana wraps. If you were connected to shore power it would probably go through the safety ground of the plug and blow out some of the electrical systems in the trailer and power pedestal. In any situation with lighting activity it is best to refrain from operating electrical devices, and stay put. I will consult my lightning protection materials and follow up later with any other information.

Fyrzowt · 06-13-2007, 10:55 PM

While aluminum conducts better than steel, both are conductive metals, on wheels. Not much difference IMO. On the other hand, there is no "Phd" behind my name. That truly makes it just my opinion doesn't it...
Dave

wanderer1 · 06-13-2007, 10:56 PM

Hello rusty,I've heard something 'bout rubber tires keeping you safe in a car,I guess it would if be safe when towing or unhooked to power/water.Gary may be right on when plugged in.I do know semi's pulling tankers w/gas/oil have ground straps that drag the ground as they travel.Not 100% sure,but think this is done in case of a lightning stike.May be for static elec. when hooked to fuel pumps.....Brian

dscluchfc · 06-13-2007, 11:32 PM

what about those stabilizer footpads on the ground??????

Buttercup · 06-14-2007, 12:49 AM

Well I can speak with some authority on this topic.

We use professional (and very expensive) lightning monitoring equipment where I work to monitor where lightning is striking near our high voltage transmission lines. A lightning strike is measured by a couple variables; Type(cloud to ground, ground to cloud and cloud to cloud), current flow in thousands of amps and multiplicity (how many times the strike... ahhh, struck). The potential of a lightning strike is in the multiple megavolt range. But as with any flow of electricity, it is not the voltage that does the damage, it is the current flow. The potential difference between the cloud and ground (or between any 2 points for that matter) is what makes the current flow.

The tires of a vehicle do nothing to insulate you from a strike. Here is some pictures of a dump truck that got into a 25,000 volt line for a half of a second. All but 2 of the tires were intact. The rest were either blown or bulging and almost blown. The dust, grease and dirt on tires help conduct the electricity.

When you are in a car you are not protected by the tires but rather by the fact that you are surrounded by metal. The metal distributes the potential all around you evenly (an equipotential zone) and therefore, if there is no potential difference, you will not get shocked. this fact is so well known in my industry that we design substations with this fact in mind. It is also this fact that allows lineman to fly to and

land on an energized transmission line and perform work without the helicopter or lineman getting blown to smithereens

.

So for the airstream the same is true, you have a metal shell that will dissipate the strike over the entire body of the trailer leaving the occupants inside relatively unharmed. But the real danger may be from the sound and from any fire danger. I bet that a hole the size of a quarter would be cleanly blown from a normal strike. having the stabilizer pads down will only help conduct the current to ground, but that may save your tires so that could be a good thing.

If the trailer is plugged in than this would certainly pose some concerns because the potential from the shell is going to try to get out through whatever means necessary and that could mean some high voltages get imposed onto electronic equipment while they are plugged in. This includes battery chargers, etc. But this would be because the electricity if finding a nice path to ground through the power cord.

As a side note, in all the years I have been monitoring lightning strikes on a high voltage transmission grid I have not seem lightning be attracted to a power line more than anything else. I have not done research on this but I can say that lightning seems to hit the ground near lines as it does the lines themselves. I mention this because the lightning seems to have the same probability of striking a metal trailer as it would any other part of the ground or trees or whatever.

volvophile · 06-14-2007, 02:36 AM

Heres the theory Ive always gone by since a 9th grade physics class:
Electrical current has what is called a "skinning Effect". Where the current tends to move on the outside of the conductor. (or the actuall electrons that are moving) Substations will use large diameter pipe for high current transmission, both for cooling, and also because current wouldnt be moving through the middle of the pipe if it where solid.

Airstreams, metal cages, and cars for that matter, act like the same pipe. The current moves on the outer skin of the metal to ground and not through the inner surface.
There are some rather spectacular exibits where people are hanging out in a suspended metal cage that is being struck by bolts of lightning from a Tesla coil.
I think The heat and general violence of a lightning strike may tear up the aluminum skin, pop a few rivets and blister the zolatone, but the ocupants should be safe for the first strike.

I generally let my safety chains lay on the ground to provide a path for lightning in hopes that it would spare my $60 power cord.

Buttercup · 06-14-2007, 03:50 AM

Quote:

Heres the theory Ive always gone by since a 9th grade physics class:
Electrical current has what is called a "skinning Effect". Where the current tends to move on the outside of the conductor. (or the actuall electrons that are moving) Substations will use large diameter pipe for high current transmission, both for cooling, and also because current wouldnt be moving through the middle of the pipe if it where solid.

In the case of a lightning strike the skin effect would be negligible and perhaps non existent. Skin effect is a frequency dependent effect, the higher the frequency, the greater the skin effect. So that is not the factor in the case of a lightning strike hitting a trailer. While the arc does radiate in an very wide spectrum, each frequency only has a small portion of overall energy. The main amount of energy is in the near DC release of discharge.

Substations use aluminum pipe not because of skin effect OR cooling but rather because it is lightweight and an excellent conductor. The hollow shape of the buss works is for strength and for having a lightweight way to conduct the current. A lightweight buss is easier to support with insulators and less prone to breaking under strain. Besides, aluminum is cheap and easy to work with. But substations are not constructed that way due to skin effect or for cooling.
CLICK HERE for more info on Skin Effect.

Quote:

Airstreams, metal cages, and cars for that matter, act like the same pipe. The current moves on the outer skin of the metal to ground and not through the inner surface.

Actually, at the frequency of lightning and even a tesla coil the current will easily penetrate the entire thickness of the metal. At 60 hertz the skin effect is REALLY big! See this chart for more info. I believe that the chart shown in wikipedia may be mislabeled as skin depth when it perhaps should be magnetic permeability. But anyway...

Quote:

There are some rather spectacular exibits where people are hanging out in a suspended metal cage that is being struck by bolts of lightning from a Tesla coil.

This is what is called a faraday shield, and the purpose is not a skin effect but again an equipotential zone around the person in the cage. They are being energized at the potential of the tesla coil, but because they have the same potential all around them they do not get shocked. (yes, tesla coils operate at higher frequencies,in the megahertz range, and skin effect would be more of a concern) - but still in that case but we really are talking about 2 things here. And anyway, you need really higher frequencies to get into the range of skin effect you are thinking about here. See this article for more information.

That helicopter video I linked to in the earlier post shows faradays principal. The guy in the helicopter doesn't get electrocuted because he is at the same potential as the line, 500,000 volts. There is no potential difference between him and the energized line he is crawling on. It is the same reason birds can sit on a 25,000 line and not get electrocuted because they are also at the same potential as the line. They clearly are not protected by skin effect because they are standing on the skin and they are clearly not insulated from the line.

Quote:

I generally let my safety chains lay on the ground to provide a path for lightning in hopes that it would spare my $60 power cord.

Well that may help but I am fairly sure that the bonding of the cord neutral and ground connection will look like a lower impedance than a piece of chain laying on the ground. Besides, the trailer is connected to the ground connection of the power cord. I am betting that the cord will take a hell of a hit if it gets struck no matter what.

Roadschooler · 06-14-2007, 05:14 AM

Cool thread! Thanks for the info all, I feel most informed

markdoane · 06-14-2007, 05:51 AM

Here is a previous discussion of lightning. And another one. And a third one.

Silvertwinkie · 06-14-2007, 06:33 AM

I'd have to agree, I believe you'd be fine, unless you had a CCD and just happened to be touching the metal inside.

Buttercup · 06-14-2007, 07:01 AM

Quote:

Originally Posted by Silvertwinkie

I'd have to agree, I believe you'd be fine, unless you had a CCD and just happened to be touching the metal inside.

Well even then you would be O.K. Just like the guy in the cage with the tesla coil zapping all around you.

Silvertwinkie · 06-14-2007, 07:24 AM

Yea, I know, I was just taking a cheap CCD shot to play around with the rookies, it's why I put a

after it.

bigeasy63 · 06-14-2007, 07:51 AM

Quote:

Originally Posted by markdoane

Here is a previous discussion of lightning. And another one. And a third one.

Thanks md, I thought this would be a common topic, I've just never seen it. Plus, me and search don't jeeha.

Wow, thanks everyone. Ask for an inch...get a mile on the forums. I just wanted to make sure I wasn't camping in a 26 foot lightning rod.
Thanks bc for the in depth explanation.

bigeasy63 · 06-14-2007, 07:56 AM

By the way, twink. What is a ccd?

Kinda like when I thought you were all very rude until I learned what an SOB was on the forum.

sander17 · 06-14-2007, 08:08 AM

With all the discussion of the power cord and chains or stabilizers on the ground, don't forget that you have a metal jack post pushing down on the ground with the full tongue weight.

Fyrzowt · 06-14-2007, 09:37 AM

Quote:

Originally Posted by sander17

With all the discussion of the power cord and chains or stabilizers on the ground, don't forget that you have a metal jack post pushing down on the ground with the full tongue weight.

My jack post rests on a rubber stand

It sounds like unplugging your power cord may not be a bad idea in an electrical storm to protect your electrical appliances, etc.
Dave

overlander63 · 06-14-2007, 06:52 PM

Quote:

Originally Posted by bigeasy63

What is a ccd?

CCD= Christopher C. Deam, industrial designer that designed the nodel of Airstream there bears his initials.

Excella CM · 06-14-2007, 07:12 PM

One last thing you can do is to sacrifice a bull to Zeus now and then. I have have plenty extra

dwightdi · 06-14-2007, 07:20 PM

This is another reason the parkers at the International want you to use a metal plate under your jack stand. It gives a good ground for the trailer for the 110 volt input and also the rare occurance of lightning. The video of the guy crawling around on the 240,000 volt AC power line while it is hot is also cool. Someone sent it to me a month ago.