WAG but I would imagine something as big and wet as a human would have a pretty fair capacitance and first contact with a high-potential would result in a pretty fair old inrush current. Wouldn’t kill you but would certainly wake you up.
No, no, and thrice no*, and I briefly explained why in post #3. Not well enough it seems, so to expand, here are the ways in which you can be electrocuted by a high-voltage pylon:
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Touch the pylon while you’re earthed. You can do this by flying a kite into a line on a rainy day. Please don’t do this.
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Get close enough to the live wire when you’re earthed such that there is an electrical arc between you and the wire. This is just as effective as method 1. Please don’t do this.
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Touch 2 or more wires at different potentials, or be close enough for the gap to arc over. Please don’t do this.
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Be in the presence of an electromagnetic field large enough to induce a significant current through your body. Please don’t do this. You don’t have to be earthed to anything to make this happen, and floating in a vacuum wearing a rubber suit won’t stop it. You either need electromagnetic shielding (like an earthed Faraday cage), or you make your toes the same potential as your head by wearing a conductive suit. David Simmons’ post reveals another alternative method to the conductive suit, though I assume the insulated bucket is conductively lined inside, and the lineman is wearing some sort of conductive strap on the body that is connected to the high voltage line? It sounds quite plausible that this would work, though if I was a lineman I’d prefer the conductive suit and helicopter approach.
Induced electromagnetic fields can be nasty. You can’t run phone lines under pylons, and sometimes the field can be so strong that it’s not possible to run other electricity lines nearby. A local woman I know has a pylon at the bottom of her horse paddock, and when she installed some floodlights underneath it recently, someone from the electricity board came round to measure the field strength to see whether it was OK to erect such an installation. It was just - she could only light 3 of the 4 corners of her exercise court as the field was too strong in 1 corner, and the lights wouldn’t be allowed if they were just 2 feet higher. It was a bit marginal.
There are high EM fields in lab installations where it’s dangerous to enter if you’ve got a pacemaker or metal plate in your skull etc., but I’d imagine the effect is less under a pylon. All the same, best avoided. And nothing would persaude me to live in a house under a pylon, if only because it creates a really grim atmosphere. I don’t know whether it’s the air ionization, the EM field, or the constant crackling sound in damp weather, but pylons are not fun places to hang out.
If there do seem to be dead birds and bats under pylons, I wonder if they got fried or otherwise harmed by the electricity, or whether the high concentration of roosting creatures just concentrates the bodies in an area as and when they drop dead of natural causes?
*Don’t think I’m ungrateful though - I appreciate every post.
She could probably have done this for nothing - or at least just the cost of a few flourescent tubes - they light without any connection in the field under pylons/transmission lines.
The History Channel had a documentary on power lines with film of both methods. The arc whan connecting the probe to the line is quite impressive.
That’s true! Although one of her horses is epileptic, which may be a concern.
I wonder if you can get prosecuted for tapping into the EM field under a pylon as a source of energy? Probably.
A couple of random real examples of high EM field damage:
A hot air balloon becomes entangled in power lines, shorting several wires together and causing a blackout by tripping safety circuits in the power station. When a short is detected on a line, it is assumed that it’s an encroaching tree branch, and what often happens is a huge electrical surge is sent down the line in an attempt to vaporise the obstacle. This happened to the hapless balloonists, melting the rope holding up the basket, which then plummeted to ground. The occupants were hurt, but survived.
Offshore pirate radio station Laser 558 tried a novel approach to antenna design. Usually pirate radio ships have big masts, but Laser initially tried a different approach, opting to hoist aloft a wire aerial with a helium balloon. Strong North Sea winds notwithstanding, the system failed as the insulating kevlar rope holding the balloon aloft kept melting, and several expensive balloons were lost.
First of all, the correct term is grounded, not “earthed”. Second, the previous posters have, in fact, answered your question.
It’s true that very high frequency, high voltage fields, like those produced by a magnetron can causing heating and disruption via direct induction upon ionic compounds or electrons; essentially, they vibrate charged particles rapidly to induce thermal impulse–that is, resistive or ohmic heating–in a semi-conductive medium. This is how your microwave oven works (and you’ll find that pure, distilled water actually takes much longer to heat up than water with a chloride or potassium solution). It can also induce eddy currents in highly conductive materials; if you’ve accidentially left a piece of foil in the microwave you’ll see sparks flying off of it. (Do not do this at home, kids; not only will you get toxic gases from the dielectric breakdown of gases, you can also get dangerous arcing which may damage or overload the magnetron.) These fields are in the 2.5GHz range, though, whereas power transmission lines are typically in the 50-60Hz range (although some specialized systems are less, or even non-alternating direct current), and their fields are unguided, so they rapidly disperse.
High frequency, low power systems, like those found in electric “stun guns” can cause temporary disruption in the central nervous system, but unless this incidently affects an arhythmia in the heart it won’t cause any permanent damage.
It’s true that a fluorescent bulb can be activated by the “ambient” currents in proximity to an alternating current, especially near the leakage currents on a step-down transformer, but that’s because the bulb is filled with a free noble gas that requires only a small current to initiate and becomes even more conductive as it activiates; in fact, fluorescent lights have to be powered through a current limiting device called a ballast to prevent them from exceeding the power maximum of the fluorescent coating. Getting a fluorescent bulb to light up takes very little power.
There is some ongoing concern about the long-term biological hazards the extremely low frequency (ELF) waves have with regard to carcenogenesis and genetic dysfunction a la the alleged “cancer clusters” of children living or schooling within proximity to high tension power lines but both the epidemology and statistical correlation of these claims are inconclusive.
So, again, from a low frequency, high voltage source like power lines, the only immediate threat is conducting from a high potential to ground or a different potential. If you are tap-dancing on the line without any connection to another conduit, your biggest danger is slipping and falling. The only way you are going to suffer electuction is if you grab the other wire for balance.
All the same, stay off the power lines, kids. We don’t want another one of those cascading multi-state blackouts. :dubious:
Stranger
Fridgemagnet is from the UK where the proper term is earthed.
I don’t have a dog in this hunt except for I can add this data point.
If I ride my bike with a wireless heart rate montior/ speedo / pedal cadence under high tension lines my heart rate goes to zero, my speed goes to 68 mph, and my pedal cadence goes to 200. :eek:
First time it happened I thought either my heart rate monitor was bad, or I was dead.
I am sure the speed/cadence displayed has to do with the frequency of the high tension lines, I just have never done the math to find out.
Fridgemagnet, as so many of us keep saying, there is no danger if all you are doing is touching power lines without grounding yourself. You keep giving examples of grounds that are irrelevant to that answer.
What you don’t do is respond to any of our comments. What is your proof that any birds feel a “tingle” when just grasping a power line? What is your proof that larger birds are in more danger? What is your proof that an arc can be made to wet earth from someone just hanging from an overhead power line? What is your proof that any power lines can induce a significant current through a human body just by themselves?
Yes, there is an electrical field around power lines. It can make fluorescent bulbs light up. It can affect electrical equipment. So what? What is your proof that this field is of killing strength without a ground? Please note that despite decades of controversy the current consensus is that power lines don’t even cause cells to become cancerous.
Your OP was about apples. When we objected to its assumptions you keep taking out oranges. Nobody is disputing the part about oranges. But your apple comments are simply wrong.
Exactly - what I’m saying is that there will be a voltage induced across your body in the presence of an electromagnet field, with or without being earthed*, and if I’m stubborn in my refusal to accept that hanging off a single high voltage wire suspended in space is safe, it’s because it’s potentially dangerous, and I dispute any statement to the contrary. Exactly how unsafe I’m not sure, and that’s essentially what I was asking in the OP.
One last time:
You’re floating in deep space, wearing an insulated suit. You’re approaching a single length of cable at a high potential and carrying a high current. There’s no fucking ground for 3 light years. The electromagnetic field will induce a current in your body, due to the fact that the EM field is stronger at one end of your body than the other because the field strength reduces with distance. At some point, the induced current in your body will make you ill, and at higher levels than this it will be fatal. It’s just a matter of degree. Read chapter 2 of this Non Ionizing Radiation and Fields H&S doc from the University of California Lawrence Livermore National Laboratory if you don’t believe a current can be induced in the body without it sharing a ground reference with the radiating EM field.
There’s a similar analogy with gravity. If you’re standing up, the gravitational pull on your head will be a teensy bit smaller than the pull on your feet, which are a bit closer to the centre of gravity. Try the same experiment where the gravity is much stronger, say near a black hole, and the difference in gravitational force between your head and your feet will tear you asunder.
Stranger on a Train makes a fair point about the fluorescent tubes. It doesn’t take much current to strike them. As a child, I made a crude test device for air ionisers that consisted of a small ceramic capacitor in parallel with a minature neon bulb. I would hold one end of this arrangement, and wave the free end near the ioniser emitter. The charge would build up a voltage on the capacitor, and when the striking voltage of the neon was reached (typically 60 to 100V) it would flash over, and the charging would begin again. Thus the flash rate of the neon was roughly proportional to the charge of the air. Relative to earth, on this occasion, but the only current it drew was from the ionised air molecules.
*Thanks Rick! Where I’ve used Earth, it refers to the planet; earth = conductive connection to the Earth, like a big chunk of metal buried in damp soil. We also use the term “ground” in the UK, where it refers to any zero reference, like the OV line on the power supply of your PC. This ground may or may not be connected to earth/The Earth.
And the answer is: not at all.
Nobody is disputing this. What everybody is saying is that it’s negligible for standard high-voltage power cables.
You keep pulling imaginary super-powered voltages out of thin air. Maybe they exist in some lab someplace. But they have no place in answering your question. For real world situations, the current induced is enough to light a fluorescent tube. But that’s it.
But the fact is, an ungrounded connection to a ELF-power transmission line at any voltage is not dangerous. Not at all. Even if the wire is bare, the conductivity of the human body is so low in comparison to the copper or copper-clad wire that scarcely any current will go through your body. See [post=6687165]this post[/post] for a better explaination of what current, with reference to AC power, is, but suffice it to say that the induced currents in a body near or even in conductive contact with a metallic conductor are minimal unless they provide a conduit to ground.
You cite Lawrence Livermore Labs ES&H, Vol II, Doc 20.7, but take a look at Section 3.2, Subradiofrequency Fields (0-4000 Hz electric, >6-300 Hz magnetic, including 60 Hz). The primary concern, aside from people with pacemakers, is sparking from conductor to body to ground. And they are often dealing with voltages that are substantially higher than are typically found in high tension power lines; the kinds of voltages used in partical accelerators and inertial confinement fusion initiators.
In short, if you aren’t grounded and can’t arc to ground, you will feel nothing, as any number of linesmen, who frequently work on live wires (with adequate training and protection…again, don’t try this at home) can attest. That’s the physics of it, and as stubborn as you may wish to be about it, the birds will continue to perch on lines.
Stranger
But you do have to remember to make sure that your body and the line are at approximately the same potential. The current to charge your body capacity to the line voltage can be dangerous.
This current has nothing to do with any currents induced by the EM field around a power line which, as has been said over and over, are negligible.
I recall seeing the documentary about the helicopter linemen working on the high-voltage pylons. Apparently, it is a very specialized job with a very low mortality rate thanks to strict adherence to safety measures (the threat of being grounded by something wind blown, I guess is a concern).
I also recall seeing a documentary about the first couple of generations of lineman in the late 19th/ early 20th century. They has a mortality rate of ~50%. That’s quite an electrifying 
statistic.
It should perhaps be noted that albatrosses do rather little perching, and the shape of their feet (webbed) is poorly suited to perching on a wire.
Any helicopter flying in the air builds up a charge. Quite high sometimes. So, even if all you are going to do is touch the helicopter that has been flying for a bit, you better use a grounded cable because you will get knocked on your ass if you don’t. No transmission lines need to be near.
Now, put that repair man in an plastic bucket or a helicopter, the first thing that you need to do is get everybody on the same page. So you stick out a stick and watch the pretty sparks. Then you attach some line between you and the other guy, be it a transmission line or the helicopter so that the static charge can not build again nor can the develop any difference ion potential between the bucket / helicopter the repair man is using.
Now, if we restrict our problem to 50 or 60 cycle alternating current at 72,000 KV or less, the amount of charging up of the guy in the bucket / helicopter is not nuff to harm him. If they discharge any major difference before he reaches out of the bucket /helicopter himself.
Playing in an particle accelerator is a whole different kettle of fried fish.
Wanna see spooky, watch the line clearing helicopters with the long cable / shaft with a 20 foot blade on the end that they fly along the lines clearing brush and growing trees. I think the line / shaft is insulated or is fiberglass but I’m not sure.
Got to have some brass ones to do that work.
I used to patrol some power lines from fixed wing aircraft but that is not nearly as dangerous.
While working for Pike Electric in Florida during the summer (My dad is a journeyman lineman that worked for Georgia Power and I have seen him work barehanded many times, though my dad is very experienced and has never even had a “flash”) I got the chance to touch a live primary (14,400 volts) barehanded. Even though you know its safe its still scary and all your instincts scream don’t touch! You can hear the electricity and even feel it while your hand is on the wire. It really is an interesting line of work. An interesting fact I learned is that if the neutral were to break it in effect becomes a primary and can kill you. Once while we were moving the Primary from one pole to another the guy in the bucket dipped the primary into the neutral and ZAP! crazy electric ball too bright to look directly at. The guys directly under it said they could feel the heat from 50 feet. Some guys told me that in cases they’ve seen where a downed powerline hits the ground it actually crystallizes the concrete. I look forward to it next summer. 
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- I heavily suspect that this effect is not significant (as long as you don’t have a pacemaker). If it were, birds would be getting killed just for coming so close to high-voltage wires. Birds are physically smaller than a human of course but they would have lower sensitivity thresholds as well. If you were dealing with RF waves/shortwaves I’d bet it would be possible but the wavelength of a 50 or 60 Htz signal is much longer than any dimension of the human body.
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- I heavily suspect that this effect is not significant (as long as you don’t have a pacemaker). If it were, birds would be getting killed just for coming so close to high-voltage wires. Birds are physically smaller than a human of course but they would have lower sensitivity thresholds as well. If you were dealing with RF waves/shortwaves I’d bet it would be possible but the wavelength of a 50 or 60 Htz signal is much longer than any dimension of the human body.
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If the cable was stranded I suspect what you were hearing and feeling was the mechanical working of the cable strands as a result of the magnetic vields associated with the currents ub the strands.
Such noises are not unusual in transformers as the windings and core laminations vibrate slightly in response to the magnetic fields.
Maybe that’s for the best, as their 3.5m wingspan might be enough to bridge adjacent cable runs. It would explain the lack of perching ducks too.
pool, you may have been feeling several things when you touched a 14.4kV live wire. It could be the corona discharge from the HT, a fluctuating ion wind, or the direct effects of an electromagnetic field on the flesh (the latter only if you’re particularly sensitive for a 14KV line). Or combinations thereof.
As there’s been some raging debate as to what levels of electromagnetic fields are generally considered safe, I thought I’d better do some research and provide some typical (and quantifiable) figures. Without entering in the whole mobile-phone health risk debate, it can be stated that a high enough electric field will kill you or at least make you sick, and a low enough electric field will be harmless. Not electrocution or static discharge, just being in the presence of an electric field. It may even be that a certain low level of EM exposure is beneficial, in a similar way that a small amount of particle radiation seems to stimulate the immune system. I don’t know, and nor does anyone else yet. Plenty of studies have been done that prove biological effects of EM fields, but what hasn’t been proved is whether these biological effects are harmful on a macroscopic scale.
Some figures: Standing below a 220kV transmission line will expose you to an electric field of between 0.2 to 3kV/m. The induced currents from this exposure would only be a few mA per square metre, and the induced currents from exposure from any electric field below about 50kV/m shouldn’t give rise to any physical sensation, though sensitive people may feel as little as 1kV/m. . Cite: National Radiation Laboratory, Ministry of Health, New Zealand.
The government of Bruei Department of Electrical Services recommend maximum daily exposure times to high EM fields - below 2 hours/day for 30kV/m; below 5 hours per day for 12kV/m; and unrestricted time below 2.6kV/m.
The International Commission on Non-Ionizing Radiation Protection (IRPA/INIRC) Guidelines specify a maximum field strength exposure for workers of 25kV/m, and then only for a limited period. People fitted with heart pacemakers should avoid fields higher than 1kV/m.
For 220kV transmission lines, the field strength at ground level is about 7kV/m, but if you’re a bird actually sitting on the wire, this is significantly higher. How high I don’t know, as all the electric field strength measurements I can find are at ground level. Crops in fields subjected to an electric field strength of 20kV/m or greater show signs of leaf damage, due to heating effects on the leaf tips during corona discharge. It might be suggested that feather tips on birds may experience some localised heating due to corona discharge, though probably this would be less damaging to a feather than a leaf.
Interestingly, it’s well known that it’s not a good idea to site bee hives underneath pylons. Bees are very sensitive to electric fields anyway, but what seems to do them harm in this case are little electric shocks from the hive. Many migratory birds are also sensitive to EM fields, and may even avoid areas of high field strength.
In conclusion, I might posit that birds indeed don’t get spontaneously fried on high voltage transmission lines, and that the majority of bird fatalities from power cables can be traced to electrocution from bridging adjacent wires. Indeed, it is usually the lower voltage (<70kV) lines that produce the most fatalities, as the cables are strung closer together than with higher transmission voltages. However, it seems that many birds would be breaching health and safety guidelines when they perch, though they probably for the most part get away with it.
Just to muddy the waters, we haven’t even talked about magnetic fields. These have health implications too!
Thanks to everyone who posted, particularly the linemen anecdotes, they were most illuminating.
There is no lack of perching ducks.
Firstly it’s good of you to posit what is a well established fact.
Secondly the vast majority of bird fatalities from power cables seem to be the result of birds striking the cables in flight. Birds have evolved to cope with branches that are connected to the ground via a thick trunk. Branches that float in empty space they don’t cope with so well.
Are you sure that isn’t because lower volatge cables are thinner and hence less visible? Have you compared deaths on live lines to deatsh on non-functioning lines?
There are bird H&S guidelines? You do know that it’s completely invalid to try to apply human guidleines to an animal with a lifespan of less than 15 years?
Given the number of crows nests I’ve seen on high tension pylons, and they all seem to produce healthy young, I doubt this is too great a concern to a birds.