The Demilitarized zone between the Koreas has electric fencing. It is around 150 miles long.

1) Doesn't the entire setup need a small power plant? How much power will such a fence pull?
2) Don't they need to worry about power dissipation and power loss over such a long distance of 150 miles?
3) How do they expect to electrocute people? Do they expect the electrons to go from the live wire, through the person and then into the earth ground?
4) Do you think they need transformers every few miles to take care of voltage drop?
5) Is the wire bare, without insulation? I think it would be bare. I don't see any point in having insulated wire ( I ask this because I just saw an electric fence wire on home depot, that had insulation! )
6) If you were a good guy and wanted to bring the fence down, wouldn't sticking a metal pole between the ground and the wire defeat the entire system?

Hope both the Koreas unify in peace.

 

Well, there is no current flowing until someone grounds it.

 

You are making a big assumption that is almost certainly invalid -- namely that the entire 150 miles is a single, continuous circuit. It is almost certainly segmented into many, probably hundreds if not a thousand or more, fence segments. There are probably fewer power sources, with one power source supplying power to several segments. Depending on what is available in the immediate area, some segments might be solar powered, others might be battery-powered and generator recharged, others powered by the local grid.

There are many types of electrified fence, so unless you dig up more details about the fencing they are using, it is just guess work.

Most electric fences produce a shock from the fence through the body to ground. But not all. Depends on the threat you are trying to counter and how much effort you are willing to go through. In the DMZ, there are layered defenses. Most notably, mine fields along the fence line, possibly on both sides of the fence. Also, the fence doesn't have to be powered to be effective -- it just has to convince people that the odds that it might be powered are high enough to deter anyone from tempting fate.

The metal pole to ground can be effective for some types of fences, but you may or may not know that it has actually taken down the fence grid. Many fence designs store up a charge and then periodically dump it onto the fence. If you have shorted the fence to ground, there might be no discernible effect and so you don't know if you have actually disabled it or not.

Since you didn't post a link to the fence wire that you say is insulated, there's no telling. Fence wire is often non-metallic with a few strands of conductor threaded through it, especially for fencing intended to provide a pointed reminder to stay away from it. Fence wire intended to be lethal would be different. But, in all cases, there has to be some kind of insulation between the wire and the supports. If the fence post is sufficiently insulating, that's enough.

As for how much power it consumes, that again depends on several factors. At the kinds of voltages that many fences operate, there can be enough leakage to be noticeable, but even then a typical car battery can usually provide enough energy to keep a moderately-long fence (hundred of yards) operational for days or weeks. How much energy is consumed when someone comes into contact with the fence very much depends on the purpose of the fence. It takes very little energy to make someone not WANT to touch the fence ever again; it takes a lot more energy to make them UNABLE to touch it (or anything else) ever again.

 

power is dissipated when current flows,
as there is nominally "zero" current flow, low power is all that's needed.

Hi drj,
A 12Volt electric fence driver, pulsing at 1Sec rate, draws approx 250mA average.

E

 

hi drj,
Remember, an animal electric fence is pulsed, like a car ignition system.

The fence is not continuously electrified, it is a high voltage pulse, about 1/Sec rate, lasting for about 50mSec,

This high voltage pulse is derived by passing a 12V high current pulse through the low voltage primary of an ignition coil. This 1/Sec rate primary pulse current is drawn from the 12V power source, usually a car battery, approx 4.5Amps
for approx 75mSec.

The actual figures depend upon the particular design of the pulser.
E

 

Yep, thats about 3 watts,
a car good car battery has what ?
but is that because of the circuit loss or the fence loss ?
Ok in a real circuit you and I know some current will flow due to leakage, transmission , capacitance et all
but thats approximately zero unless the wire is touched,

As a boy I was responsible for goats and that involved moving & maintaining the electric fences. I found that grass, even dead brown grass (but much more so live green grass) conducts and saps the voltage from the fence. Run a fence through a long enough patch of tall grass and you would have goats chewing the actual wire at the other end. Or one single girthy weed could do it with good contact. It became a logistical game to put the fence somewhere that did not have tall grass, which usually meant somewhere the goats had already grazed, while trying to relocate them to a place we wanted them to graze next. If the game was too hard I would cheat and get the weed eater but I would spend hours trying to plan a way to avoid it. Unless you walk the fence every Friday and take care of vegetation, it won't work, and probably wasn't working Wednesday or Thursday either but "the others" didn't know that.

I say all that to say, theoretically there is no load on the system but in practice there is: vegetation.

 

As a boy I was responsible goats and that involved moving & maintaining the electric fences. I found that grass, even dead brown grass (but much more so live green grass) conducts and saps the voltage from the fence. Run a fence through a long enough patch of tall grass and you would have goats chewing the actual wire at the other end. Or one single girthy weed could do it with good contact. It became a logistical game to put the fence somewhere that did not have tall grass, which usually meant somewhere the goats had already grazed, while trying to relocate them to a place we wanted them to graze next. If the game was too hard I would cheat and get the weed eater but I would spend hours trying to plan a way to avoid it. Unless you walk the fence every Friday and take care of vegetation, it won't work, and probably wasn't working Wednesday or Thursday either but "the others" didn't know that.

I say all that to say, theoretically there is no load on the system but in practice there is: vegetation.

Maybe you needed to look into a weed burner fence -- those have a high enough current (or, more properly, higher pulse duration) to destroy the vegetation that touches them (though I imagine there's a practical limit to how much vegetation can be in contact before the parallel paths kill the effect). But that also means that they can start grass fires.

 

Insulated fence wire is used for direct burial "underground" dog fences. Works with a collar receiver device that will deliver first an audible alarm and then a shock if approached too closely.

 

I understand he avoided the electric fence by going on a guided tour, and running into the arms of the north Korean guards..
much easier than worrying about fences.

Who is "he," what guided tour, WTF are you talking about?

 

Who is "he," what guided tour, WTF are you talking about?

He's referring to the U.S. soldier that is in North Korean custody.

@drjohsmith : Let's keep the thread on the topic of electric fences.

 

@strantor
for my interest, could you expand on what you mean by "WTF"
Here in the UK, thats a very aggressive / abusive comment

It all depends on context. It's often meant to just convey amazement or confusion or surprise.

 

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