This may seem like an inane question but I suppose that’s what this site is here for. I promise this is not for any personal use. My friends and I were having a rather dorky conversation about the electrical properties of an electric fence. Having noted earlier that one can dangle from a power line and be safe because you are not grounded we wondered if the same applied to electric fences. Now obviously if you just walk up and touch one, you’re in for a shock but what would happen if you took a running leap onto it? Theoretically I don’t think you’re grounded. However, multiple movies (stunning reference I know :)) have shown me that this doesn’t work. Why? The only thing I can think of is that there is some kind of voltage difference between the different contact points on the fence. Any other dopers smarter than me or with actual electric fence (we’re talking the big security kind here, not for livestock) experience?
Well, I suppose a smart design for an electric fence would be a series of closely-spaced parallel horizontal wires with alternate live and earth charges. I don’t know if this design is actually used though.
Most electric fences are really one charged wire on little insulated standoffs. The rest of the fence is not usually live, but it might be grounded. If you touched both the live wire and the grounded part, it would bite you.
My brother once had an exceedingly stupid and amorous Irish Setter. One day the dog climbed over an electric fence to go carousing. He howled and yelped as he climbed, but his lust was strong; he did not turn back. Nor did he ever come back home.
Getting back to the OQ, It might be possible to hop onto the hot wire and get over, but it would be a feat of balance.
What about those electrified chain-link fences around prisons and such? Or that fence the little kid was hanging on in Jurassic Park.
What follows is not really pertinant to the OP, but I had a male collie many years ago that peed on an electric fence, gave one hell of a yelp, and dashed home to hide under the porch for the next few hours. I know it was evil of me, but I could not stop laughing.
IIRC, I think I could just make out little wires running between the big wires in that particular scene. But it’s been a while since I’ve seen the movie.
IANA physicist and I know little about electricity, but I do have experience with being shocked by an electric fence. i’m sure somebody will stop by and explain how they work, but my understanding is that they operate on timed pulses. If you have a very long fence you can actually hear the crackle as the electricity travels down the line and around the loop. The top wire is usually the only electrified one.
Because of the pulse nature of the charge, tapping your fingers on the wire to check if its on won’t always work. I’ve made this mistake before. Tap fence, seems fine. Grab it as I’m vaulting over and YOWZAH!!! And that thing about not touching the ground and not getting shocked (just like the squirrels do it!) isn’t true. Power lines are insulated. Without it, they shock anything, even if it wasn’t touching the ground. Haven’t you ever seen a squirrel or bird that was cooked because it gnawed through the insulation on the wire, despite being midway between the telephone poles and nowhere near anything that could ground them? Well, electric fences have to be insulation-free to work. So you can get shocked even if you’re in midair. And it hurts.
I’m not an expert on electric fences but I do own several "fencers.
Thats the box that produces the high voltage.
Its done in pulses.
Sometimes over 9Kv.
The pulses are somewhere around a second apart.
Thats why mcbiggins could touch the wire and not get shocked.
Sometimes ,for cattle, you run 3 wires. bottom a HOT wire. middle the common wire. the top another hot wire same as the bottom.
Animal can get shocked from the bottom to ground or sticking his head between the center wire to either top or bottom.
The common wire from the box must be to a stake driven into the ground and
Don’t know how fences electrified for prisons etc is done.
The thing about not touchingthe ground or any other wire and not getting shocked from over-head powerlines is true. Also overhead cables do not have any insulation on them at all. In electrician college we were told that the thickness and weight of the insulating material would be too large to be economical.
IIRC if there was a thin layer of insulation on a power cable and you grabbed it whilst being earthed you would still get the shock because the ‘aura’ or whatever ( I can’t remember the proper terms) of the electricity in the cable fill a certain size of air around the cable.