jroersma@orion.oac.uci.edu (John Roersma) (12/28/89)
Please help settle an argument regarding shocks from electric fences. My parents both grew on farms with electric fences which would give a strong shock when touched. They have told me that they had experiences where some kids would grab another person (or persons) and touch the fence, and that the person at the end of this human chain would get the (worst) shock (!). Why does the person on the end of the chain (the person farthest from the fence) get the shock, assuming each person has roughly the same arm-to-arm and arm-to-ground resistance. Modeling this as a resistive network shows that the person in contact with the fence will experience the largest arm-to-ground voltage drop (hence the largest current and largest shock). I have tried to state my case to my parents, although they have had the opportunity to experience the shock at both ends of the "chain", and will swear that the shock _is_ worse at the far end! Who's correct here? Have I made an oversight, or is there some other physical phenomenon involved? +---------------------------------------------------------------------+ John Roersma jroersma@orion.oac.uci.edu Dept.of Electrical & Computer Enginering jroersma@ucivmsa.bitnet University of California, Irvine >> this space available for rent << +---------------------------------------------------------------------+
jmasters@pcocd2.intel.com (Justin Masters ~) (12/28/89)
In article <3858@orion.cf.uci.edu> jroersma@orion.oac.uci.edu (John Roersma) writes:
+
+
+Please help settle an argument regarding shocks from electric fences.
+My parents both grew on farms with electric fences which would give
+a strong shock when touched. They have told me that they had
+experiences where some kids would grab another person (or persons)
+and touch the fence, and that the person at the end of this human chain
+would get the (worst) shock (!).
+
+Why does the person on the end of the chain (the person farthest
+from the fence) get the shock, assuming each person has roughly
+the same arm-to-arm and arm-to-ground resistance. Modeling this
+as a resistive network shows that the person in contact with
+the fence will experience the largest arm-to-ground voltage drop
+(hence the largest current and largest shock).
+
+I have tried to state my case to my parents, although they have
+had the opportunity to experience the shock at both ends of the
+"chain", and will swear that the shock _is_ worse at the far end!
I'm hoping I'm right here...
From what I understand, the resistance between two people is much smaller than
the resistance through a body, your shoes, etc, to the ground. What this does
is use the arm to arm linkage as a short, passing the current down to the last
guy who gets shocked. I would assume that if the last guy is on a wooden
platform without any way to conduct to ground, then the person before him
would get a shock. If I'm wrong, let me know.
+Who's correct here? Have I made an oversight, or is there some other
+physical phenomenon involved?
+
+
++---------------------------------------------------------------------+
+John Roersma jroersma@orion.oac.uci.edu
+Dept.of Electrical & Computer Enginering jroersma@ucivmsa.bitnet
+University of California, Irvine >> this space available for rent <<
++---------------------------------------------------------------------+
-----------------------------------------------------------------------------
Fireman to homeowner: At one point we | Justin Masters
decided to fight fire with fire... |
basically your house burned even faster. | jmasters@fmdgr1.intel.comamichiel@rodan.acs.syr.edu (Michielsen) (12/28/89)
In article <3858@orion.cf.uci.edu> jroersma@orion.oac.uci.edu (John Roersma) writes: >... regarding shocks from electric fences. >... some kids would grab another person (or persons) >and touch the fence, and that the person at the end of this human chain >would get the (worst) shock (!). > >Why does the person on the end of the chain > >Who's correct here? Have I made an oversight, or is there some other >physical phenomenon involved? > My guess is two sided. First, the middle person has 2 current paths. 1 to Gnd, 1 to the next person. The resistance to gnd is much > than that to the next person, and most of the current goes to the next person. The neural paths from hand to foot go through the spine which is integral in it's connection to the brain & hence pain. The pathway from hand to hand while does cross the spine, it does not run 'with' the spine, and there are enough muscle cross connects between the 2 hands that ths brain receives less pain info. Secondly, the 'grabber' is prepared for the shock & pain. While the 2nd person the 'shockeee' is surprised. Pain prepared for is < the surprise pain. Lastly - This reported experience is true. I've done it myself. I have never seen a fence that will hurt a person. (they are illegal) The shock will make the inexperienced think they are about to die at any moment, but they can't. You can feel free to play with it grabbing it & swinging you hand making 'surprise' contacts. My experience is that no matter how familiar or experienced with it you are, the 'surprise' shocks hurt more than the intentional ones. )8-}} al
jim@mmsac.UUCP (Jim Lips Earl) (12/29/89)
If all the "shockees" were standing on a board (or some other
insulating material except for the last person in the string, they
would all feel the shock the same. Remember that current flows thru
each element equally in a series circuit, despite resistance
differences. Voltage now, that is a different story. If one person's
body had higher resistance than another's in the string, more voltage
would be developed across that person's body.
--
Jim "Lips" Earl UUCP: ucbvax!ucdavis!csusac!mmsac!jim
KB6KCP INTERNET: mmsac!jim@csusac.csus.edu
=======================================================================
The opinions stated herein are all mine.jeffg@shamu.WV.TEK.COM (Jeff C. Glover) (12/29/89)
In article <1628@rodan.acs.syr.edu>, amichiel@rodan.acs.syr.edu (Michielsen) writes: : In article <3858@orion.cf.uci.edu> jroersma@orion.oac.uci.edu (John Roersma) writes: : >... regarding shocks from electric fences. : >... : ... : You can feel free to play with it grabbing it & swinging you hand making : 'surprise' contacts.... Don't "feel free" to try this if you don't know for sure that the folks being 'surprised' aren't wearing pacemakers. Pacemakers are known to be sensitive to such voltages.
random@cbnewse.ATT.COM (Random @ rebmA) (12/29/89)
> : >... regarding shocks from electric fences. > : You can feel free to play with it grabbing it & swinging you hand making > : 'surprise' contacts.... If a current pulse follows a path from arm to arm, the the solar plexus/cardiac nerves may be overridden sending the heart into ventricular fibrulation (or cardiac arrest). Then the hogs eat you. Random
ritchie@hpldola.HP.COM (Dave Ritchie) (12/30/89)
I think the point contact of the last person to ground causes a higher current density thru the discharge point than the current conducted through palm to palm contact. This is not dissimilar to the reasons that the static electricity shock received when touching a doorknob with your bare hand is much more painful than when touching the doorknob with a key. But what do I know -- I'm only a software guy :->. Dave Ritchie
Nagle@cup.portal.com (John - Nagle) (01/01/90)
Commercial electric fence chargers apply a pulse every half-second
or so, specifically so that if a human or animal gets in contact with
the fence, they don't get muscle-locked to it.
Some of the higher-powered fence chargers are powerful enough to burn
off weeds contacting the fence. This is considered a feature.
John Naglevince@tc.fluke.COM (Craig Johnson) (01/03/90)
A couple of years ago I went out and bought the cheapest "fence charger" I could find (to keep the dog out of the garden) and when I got it home and checked it out I found that it consisted of NOTHING MORE THAN AN AC LINE CORD AND TRANSFORMER mounted in a plastic box. There was no fuse, no interrupter, and nothing to limit current other than the physical properties of the transformer. Guess what? it WAS NOT UL approved! Needless to say, I was concerned about the safety of this thing, so I decided to see just how much of a shock it could produce and whether a person could safely handle it. Not wanting to risk my life checking this out, I devised to unground myself, connect one electrode to my wedding ring, and use a second electrode to tap the back of the same finger. This was done, of course, to limit the current path to a single finger and keep it as far as possible from more critical body areas. I don't remember at the moment how the second electrode was situated, but I'm sure I didn't hold it in my other hand! Then using a resistor substitution box, and starting at a very high value, I varied the input to the transformer, shocking my finger, until I reached a point where I decided it was unsafe to proceed further. I don't remember the voltages measured, but I recall stopping at 1/3 to 1/2 of the way to full zap. The "charger" was returned to the dealer the next day. Eventually, I constructed my own fence zapper based on pulsing an automotive ignition coil, which was much safer. The zapper I ended up with only caused mild discomfort to people, but was very effective on a dog's wet nose and he was quickly convinced to stay out of the garden. The moral: Don't assume all electric fences are safe to grab! You may be betting your life if you are wrong! WARNING - I do not advise anyone to test "fence chargers" by shocking themselves. This practice could result in your death! (No smilely on this one). DISCLAIMER - Nothing expressed in this posting is intended to represent the views or advice of the John Fluke Mfg. Co. ------ Craig V. Johnson ...!fluke!vince John Fluke Mfg. Co. Everett, WA
ee5391aa@hydra.unm.edu (Duke McMullan n5gax) (01/03/90)
The physics discussion following this article has been enlightening, but we
haven't yet considered physiology or psychology.
Some people have a substantially higher skin resistance than others (and we'll
forgo the "poor conductor" joke at this point) -- this is the physiological --
and the reaction to a given shock (constant current, for reference) can vary
enormously among individuals -- that's the psychological.
I speak only for myself, but MY reaction to an electric shock varies greatly
with situation, time of day, state of mind, phase of the moon, etc. One of the
worst shocks I ever got...naw, that's a story for another time.
The whole point here is that it's VERY hard to establish that the geek on the
end of the line actually gets the hardest shock. For that matter, exactly what
is meant by the "hardest shock"? He screams the loudest?
Think it over.
On a subject whose Hamming distance from the above isn't very great, no doubt
you've heard stories about people micturating on an electric fence, ignition
coil, or other source of HV. I'm skeptical of them, categorically. Want to
know why? Just take a strobe unit (photographic will do, but repetitive flashes
will be better) with you the next time you go in for a number one. Try for a
fairly dark bathroom. As the waters flow, fire that strobe. Look CLOSELY at
that stream. Now, are you skeptical too?
d
Fortunate is he for whom the belle toils.
Duke McMullan n5gax nss13429r phon505-255-4642 ee5391aa@hydra.unm.eduridder@elvira.enet.dec.com (Hans Ridder) (01/03/90)
In article <1211@ariel.unm.edu> ee5391aa@hydra.unm.edu.UUCP (Duke McMullan n5gax) writes: >On a subject whose Hamming distance from the above isn't very great, >no doubt you've heard stories about people micturating on an electric >fence, ignition coil, or other source of HV. I'm skeptical of them, >categorically. When I was young, my older brother once relieved himself on an electric fence (in Germany if it matters), and by the surprized look on his face, the jumping and the way he "held" hiself (making himself wet in the process), I would venture to guess that he did indeed receive an unpleasant shock. While this isn't first hand (so to speak) evidence, I'm certainly convinced not to repeat the experiment. -hans ======================================================================== Hans-Gabriel Ridder Digital Equipment Corporation ridder@elvira.enet.dec.com Customer Support Center ...decwrl!elvira.enet!ridder Colorado Springs, CO
witters@tc.fluke.COM (John Witters) (01/04/90)
In article <13569@fluke.COM> vince@tc.fluke.COM (Craig Johnson) writes: >The moral: Don't assume all electric fences are safe to grab! You may >be betting your life if you are wrong! Let me add to this. When I was a kid we had an electric fence charger we used to keep our cattle from knocking down fences. The charger ran off the AC mains and had a step up transformer in series with an interrupter and with fuses on both the primary and secondary. The interrupter applied power to the fence for one second every two seconds (i.e. a 0.5 Hz square wave). One of the advertised features of this charger was that the arc it put out would cut down any weeds that happened to fall or grow into the fence. We used pieces of insulated wire to electrify sections of the fence. One morning I went out to do something and I grabbed the insulated wire to disconnect a section of fence. As it happened, there was a hole in the insulation where I grabbed it. Since it was morning, there was dew on the ground, and since it was summer, I was barefoot. Well, the interrupter applied power to the fence, and I found myself paralyzed for the next second until the interrupter removed power. While I was standing there I smelled something burning. When I was able to remove my hand from the wire, I found a small hole etched into the skin on my thumb. I didn't think much about it at the time, but now I realize that the interrupter may have saved me from something worse than a sore thumb. Next Time: What happened when my dog pissed on the fence. -John -- * * * John Witters voice: (206) 356-5274 * \ * John Fluke Mfg. Co. Inc. * \ * P.O.B. C9090 M/S 245F fax: (206) 356-5116 * P A G\I N G * Everett, Washington 98206 or (206) 356-5174 * \ * * \ * domain: witters@fluke.COM * * * uucp: {sun,microsoft,uw-beaver}!fluke!witters
jeffw@midas.WR.TEK.COM (Jeff Winslow) (01/04/90)
In article <1211@ariel.unm.edu> ee5391aa@hydra.unm.edu.UUCP (Duke McMullan n5gax) writes: >On a subject whose Hamming distance from the above isn't very great, no doubt >you've heard stories about people micturating on an electric fence, ignition >coil, or other source of HV. I'm skeptical of them, categorically. Want to >know why? Just take a strobe unit (photographic will do, but repetitive flashes >will be better) with you the next time you go in for a number one. Try for a >fairly dark bathroom. As the waters flow, fire that strobe. Look CLOSELY at >that stream. Now, are you skeptical too? Maybe you should see a doctor for that. :-) Or maybe the flash of the strobe causes a slight involuntary muscle contraction? Or maybe I'm just micturating into the moving atmosphere. Jeff Winslow
bill@flash.UUCP (William Swan) (01/04/90)
In article <13591@fluke.COM> witters@tc.fluke.COM (John Witters) writes: >>The moral: Don't assume all electric fences are safe to grab! [...] >Let me add to this. [...] >Next Time: What happened when my dog pissed on the fence. An acquaintance of mine a couple decades ago relieved himself against an electric fence (he'd failed to note the insulators) while out hunting. As he put it, for several days after he and his wife thought their child-bearing days were over for good. They weren't, though. At least not until after he underwent his *third* vasectomy. -- Bill Swan bill@Summation.WA.COM Send postal address for info: Innocent but in prison in Washington State for 13.5 years: Ms. Debbie Runyan: incarcerated 01/1989, scheduled release 07/2002. In now: 0 years, 11 months, 2 weeks, 0 days.
thomas@mvac23.UUCP (Thomas Lapp) (01/05/90)
> On a subject whose Hamming distance from the above isn't very great, no doubt > you've heard stories about people micturating on an electric fence, ignition > coil, or other source of HV. I'm skeptical of them, categorically. Want to > know why? Just take a strobe unit (photographic will do, but repetitive flashes > will be better) with you the next time you go in for a number one. Try for a > fairly dark bathroom. As the waters flow, fire that strobe. Look CLOSELY at > that stream. Now, are you skeptical too? Beg to differ, but since HV sources are just that -- High Voltage sources -- I would think that they have the capability to cross a small gap between two conductors. Now since body fluids are pretty good conductors, wouldn't it be at least POSSIBLE that given the right voltage and conductivity, that it MIGHT work? - tom -- internet : mvac23!thomas@udel.edu or thomas%mvac23@udel.edu uucp : {ucbvax,mcvax,psuvax1,uunet}!udel!mvac23!thomas Europe Bitnet: THOMAS1@GRATHUN1 Location: Newark, DE, USA Quote : Virtual Address eXtension. Is that like a 9-digit zip code? -- The UUCP Mailer
ghg@ucbvax.BERKELEY.EDU (George Goble) (01/07/90)
25 or so years ago, when I was a kid on the farm, I measured *our* electric fence. It was approx 2100V @ 30MA, one sec on, one sec off. It did not turn completely *OFF*, but dropped to a few hundred volts at a few ma (enough to let go), the interrupter was a plug in "can" and seemed to wear out every few months. It did burn weeds (ants, horseflies and other things we connected it to). Horse flies, after burning and smoking, would "revive" and fly away after 10 mins or so! I (not the fence) moved up to 15-KV neon sign transformers after that. Those turned ant hills into glass. My dad once "grazed" a the fence wire with the top of his head, and he was instantly down in the dirt. A friend of mine, whizzed on the fence at point blank range, it knocked him down too. --ghg
ee5391aa@hydra.unm.edu (Duke McMullan n5gax) (01/08/90)
In article <33514@ucbvax.BERKELEY.EDU# ghg@ucbvax.BERKELEY.EDU (George Goble) writes: #I (not the fence) moved up to 15-KV neon sign transformers after that. #Those turned ant hills into glass. # #My dad once "grazed" a the fence wire with the top of his head, and he was #instantly down in the dirt. A friend of mine, whizzed on the fence #at point blank range, it knocked him down too. # #--ghg Ahem. Where I come from, we call this "natural selection". ZAP! d Fortunate is he for whom the belle toils. Duke McMullan n5gax nss13429r phon505-255-4642 ee5391aa@hydra.unm.edu