How easily can a high amperage electric fence be shorted out?

[callie123]

Researching for a Scifi novel that depends heavily upon electricity...something I don't know much about! Any input would be appreciated!

My situation: Somebody is trying to sneak through a high powered electric fence. Is it at all feasible to short out the fence somehow -- like, connecting it to a rod into the ground (without getting shocked lol). I know that electric fences can short out...but my scenario would be dealing with lethal currant levels.

 

[Drakkith]

Yes, you can simply connect the fence to ground by using a metal stake and a wire. This should blow the fuse for the fence, shutting it down.

 

[callie123]

Thank you, Drak :-) Since powerlines let out a pretty mean fireball when they short, would this scenario cause a lot of sparks, fireworks, that kind of thing?

 

[sysprog]

Yes, you can simply connect the fence to ground by using a metal stake and a wire. This should blow the fuse for the fence, shutting it down.

Well, a good electric fence charger may have a detector for an open or short circuit, and may turn on a short circuit alert lightbulb or audible alarm if you simply ground it out somewhere along the wire. For a story, the MacGyver-type character can use an insulated wire to make a parallel bridging connection around the section of electric fence he wants to sever, and then clip through the fence without fear of setting off a circuit anomaly detector.

 

[sysprog]

Thank you, Drak :-) Since powerlines let out a pretty mean fireball when they short, would this scenario cause a lot of sparks, fireworks, that kind of thing?

A typical fence charger runs maybe 10-100 joules, requiring roughly 1 joule for 5 miles of 1/4" wire -- it's not going to spark at the ground like a storm-downed power line. You can have your character test it for power by laying a fresh cornstalk or piece of tall grass on it with an ungloved hand 1 or 2 feet away from the wire to feel for the pulse ...

 

[callie123]

A typical fence charger runs maybe 10-100 joules, requiring roughly 1 joule for 5 miles of 1/4" wire -- it's not going to spark at the ground like a storm-downed power line. You can have your character test it for power by laying a fresh cornstalk on it with an ungloved hand 1 or 2 feet away from the wire to feel for the pulse ...

So, if the joules were increased, at some point would there be noticeable sparks? haha I'm not a pyromaniac, but it's a possible plot point.

 

[callie123]

Well, a good electric fence charger may have a detector for an open or short circuit, and may turn on a short circuit alert lightbulb or audible alarm if you simply ground it out somewhere along the wire. For a story, the MacGyver-type character can use an insulated wire to make a parallel bridging connection around the section of electric fence he wants to sever, and then clip through the fence without fear of setting off a circuit anomaly detector.

Wow, that would be so MacGyver. Thanks for the idea :-)

 

[sysprog]

So, if the joules were increased, at some point would there be noticeable sparks? haha I'm not a pyromaniac, but it's a possible plot point.

Sparks occur at the 'make or break' very short distances of circuit closing and opening. To get a spark from a fence charger, you'd have to make or break the short during the hot part of its pulse cycle. You could get a pretty good spark by just shorting the charger out across its 2 posts at the right moment, but if you shorted it for longer than a fraction of a second, maybe for even a single pulse, as @Drakkith said, you'd blow its fuse.

 

[256bits]

My situation: Somebody is trying to sneak through a high powered electric fence. Is it at all feasible to short out the fence somehow -- like, connecting it to a rod into the ground (without getting shocked lol). I know that electric fences can short out...but my scenario would be dealing with lethal currant levels.

You could also investigate the muscle response to current levels.
One may want the fence to give a surprising and hurtful jolt, but a low enough current so that a person can let go, and/or the muscles do not contract from a continuous high voltage/ current.
If the person cannot let go, then that is a continuous short - maybe that is what you want.

So one can use intermittent pulses.
The dwell time between high voltage pulses could be say 1 sec, and the length of pulse in the ms.
One doesn't want a fuse to blow, if say your cow sticks its head far enough over that it receives several shocks before backing away. The primary coil current would be fixed to increase at a predetermined rate and to break at a certain level, causing the magnetic field to collapse producing the high voltage. Thus it is ensured that one cow cannot receive several shocks, destroying the electric perimeter, enabling all your cows to run loose to greener pastures.

 

[Bystander]

See also https://www.physicsforums.com/threa...ine-2-without-a-load-in-between.960305/page-2

 

[jrmichler]

Just don't have your character do what a friend did. He told me that he tried a scientific experiment the previous day involving peeing over an electric fence. I asked how it went. He said "Pretty good, until the pressure started to drop". He was about 12 years old at the time. Since then, he raised three children, and now has about six grandchildren. So apparently there was no permanent damage.

I saw no need to replicate that experiment. I did once brush up against an electric while crawling underneath. It was a good healthy memorable zap, but not fatal.

Electric fence chargers are specifically designed to not kill people or animals.

 

[sysprog]

...but my scenario would be dealing with lethal currant levels.

Electric fence chargers are specifically designed to not kill people or animals.

That's true of the ones on cattle ranches, but not of these:
https://en.wikipedia.org/wiki/Electric_fence#Lethal_fence

(Lethal) Electric fences are used in the DMZ, which separates North Korea from South Korea.

At the 'Lethal Fence' section, the article discusses some characteristics of military electric fence installations that have lethal energy levels. These would be designed to be difficult to circumvent, so you'd need to look into some individualities of the systems in order to create a reasonably plausible fictional scenario along those lines.

A BBC article says that deer still won't cross the Czech - East Germany border even though the fences were taken down decades ago.

This reconstructed section of that border fence looks like it would be pretty challenging:

 

[Nik_2213]

Yeah, there's a world of difference between pulsed, 'warn off' systems for stock fences and field dividers, and the mega-zap versions shown above...

Against that, how covert do you want to go ? The 'insulated clips' thing is beloved of bank robbers and such, with 2nd-order alarm systems using a pulsed impedance bridge to spot attempted incursions. Think 'High End' detectorist gear.

But, if you really, really want to bust through a 'lethal force' electric fence, a full-on ram-raid with a front-mounted, V-shaped 'plow' grounded to an ample 'tail' of heavy chain on a tracked 'dozer' with Faraday cage fits the bill.

Hence the traditional tank-obstacles, mine-fields and armed guards...

Disclaimer: A colleague roof-rode one of the 'Combat Engineer' vehicles that carved routes through those vast desert berms etc in Iraq. It was apocalyptic. Like an X-rated video-game, his Engineer team raked defenders they flanked, while fanatics who'd stood and fought died screaming beneath feet of bull-dozed sand...

As he said, he'd seen the old documentaries, read the histories, but suddenly understood a LOT more about WW1's trench stalemate, and how those first Tanks changed the paradigm...

 

[member 656954]

Researching for a Scifi novel that depends heavily upon electricity...something I don't know much about!

Be mindful that sci-fi novels that deal with real stuff - physics, electricity, orbital mechanics - that you don't know about and get wrong, typically get savage reviews. Unless you keep it high-level, and let your readers fill in the gaps with their knowledge, you will be picked to pieces on the details that you missed.