Lightning and dog fence

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GerryB

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Location
woodbridge, ct. USA
Just came from a house where lightning struck a tree and followed the invisible fence wire to its source in the garage. The control unit that was plugged in to an extension melted and started a fire on the garage wall which they discovered quickly and put out. So she needs a plug installed for when they repair the invisible fence but she is worried it could happen again. There are a lot of trees on the property and the fence goes near all of them. She asked me is there a way to protect against that and I said I don't know. (I would have thought the invisible fence wires would have just melted) The tree that was struck was at least 80 feet from the house and the wire going around the perimeter to the house had to be 200 feet. Thoughts?
 
I have a similar set up using 800' of boundary wire through a wooded property. The unit I use has specific unit grounding requirements and a recommendation for lightning protection. (see attached) I would think most units have similar requirements and recommendations.

I can't say how effective this is since I haven't yet had to deal with a lightning strike like you described, and knock on wood I won't have to. I'm just happy it keeps the dogs in the yard....
 

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  • prf-304w-deluxe-in-ground-fence-manual pg 8.pdf
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I'm not exactly sure how her controller is implemented, but most have some sort of suppression for lightning (and must be connected to a grounded circuit). If that suppression is a MOV, their common failure mode is to burn up. Our Facilities people at work do not allow plastic cased power strips for that reason -- they want metal in case the MOVs burn up.

Does the fence still work (or is the buried wire still good if you need to replace the fence controller)? The buried wire needs to be insulated to function. If the lightning melted it, the wire may have to be replaced. So you can't ground the buried wire if you were wondering about that...

It is also possible, that buried wire loop just acted like an antenna and electrically coupled the lightning strike instead of being conducted by a direct strike. Hopefully, this is what you had instead of a direct strike (which probably melted the insulation on the buried wire).

All I can think of would be to put your own surge suppressor on the buried wire before it connects to the controller and use one that is in a metal can. That will take load off the suppressor in the plastic fence controller at least until it is used up. I don't know what type of voltage is put on that buried fence wire, and you'll need to know that to pick a suppressor. You could also just install the controller in a metal box to contain the fire should it happen again. But most controllers beep if the buried wire is cut, so the user still needs to be able to hear that.
 
Does the dog know it's not working?
She might not even have to replace it!
 
mgookin said:
Does the dog know it's not working?
She might not even have to replace it!
Click to expand...

Dont know about hers but mine sure do. Collars beep if they get too close to warn them and if they dont heed the beep it will give em a shock. They dont like to hear the beep and will test it if collar batteries go low.


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jtinge said:
Dont know about hers but mine sure do. Collars beep if they get too close to warn them and if they dont heed the beep it will give em a shock. They dont like to hear the beep and will test it if collar batteries go low.
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Click to expand...

My dog just braces himself and gets a running start. The shock doesn't last long if he is fast enough.

What was funny was trying to watch the kids pull him back into the yard when they didn't realize they had to take the collar off first. They didn't stand a chance - that dog wasn't budging an inch!!
 
That happened the first few times till i cranked up the loop current and expanded the width of the shock field. Once they got stuck they never tried again, as long as they heard the beeps.


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what type of voltage in on the wire? what freq does it run at? another method is to use a capacitor to earth ground, this allows lightning to to arc through the cap and find path to earth. like the MOV's, the cap will fry but should help protect the controller.

sounds like the wire had a direct hit. you also need to handle stray voltages that get into the wire from indirect hit.
 
mike_kilroy said:
In ham radio we sometimes use an air gap Proctector. Will look for example when back to a computor.
Click to expand...

air gap survives better than MOV or capacitor....

http://www.google.com/aclk?sa=L&ai=...%2Flike%2F151057370105%3Flpid%3D82&adtype=pla

or make your own:

images
 
steve66 said:
My dog just braces himself and gets a running start. The shock doesn't last long if he is fast enough.
Click to expand...
My mom had a dog that did that. The invisible fence did nothing but keep him from coming back in once he got out.
 
mike_kilroy said:
air gap survives better than MOV or capacitor....

http://www.google.com/aclk?sa=L&ai=...%2Flike%2F151057370105%3Flpid%3D82&adtype=pla

or make your own:

images
Click to expand...
at 1/4" gap i suspect the controller will still fry. 3x10^6V/meter for air. voltages less than whats need to jump air gap can still provide enough energy to perhaps cause other items to burn up, literally. if air gap, i would try and adjust the gap down to something that is close to the fencing voltage, or, keep a 1/4 or 1/8" gap but add a MOV across the screws, a MOV that is rated something close to fence voltage, etc. this way you get stray voltage protection along with that high voltage high energy scenario. with the latter the controller is still subject to damage because the dialectic strength of controller parts may be less than 1/4 or 1/8" air gap, etc. main goal is to prevent fire from starting, thus i might consider adding fire proofing around where the wire comes in to the controller and the controller itself, etc.
 
Thanks for replies

Thanks for replies

Those were a lot of good replies. I had to do some reading to find out what a MOV (metal-oxide varister) and the air gap was. The web links were also good. I can now tell the HO that there should be a way to prevent this from happening again. (I don't know how old the system was or if it was grounded other than through the extension cord. It was on the opposite side of the house from the service so I don't think they hit the ground rod as one site suggested.)
 
GerryB said:
Those were a lot of good replies. I had to do some reading to find out what a MOV (metal-oxide varister) and the air gap was. The web links were also good. I can now tell the HO that there should be a way to prevent this from happening again. (I don't know how old the system was or if it was grounded other than through the extension cord. It was on the opposite side of the house from the service so I don't think they hit the ground rod as one site suggested.)
Click to expand...

You can mitigate the risk but you can not 100% prevent damage. You are increasing their probability of not having substantial damage next time.
 
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