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Mudshark
12-27-2002, 04:16 AM
What will happen if a person touches a power line on the telephone poles?

casdave
12-27-2002, 04:21 AM
If you mean telephone poles then you'd be ok, but if you mean power poles, then you would still be ok if you were not touching anything else, or you were properly insulated.

OTOH, if you were standing on the ground and touched one with say one of those long carbon fishing poles, you stand a good chance of becoming similar material to the thing in your hand.

trader_of_shots
12-27-2002, 04:22 AM
Are ther lines themselves insulted these days ???

Mudshark
12-27-2002, 04:24 AM
What if the person was standing on the ground, and touched the power line?

Mudshark
12-27-2002, 04:26 AM
Touched it with their hands, I should add.

Ice Wolf
12-27-2002, 05:14 AM
Short answer? You'd fry.

Info on high voltage lines. (http://tva.gov/power/safety.htm)

trader_of_shots
12-27-2002, 05:33 AM
wait.. are powerlines covered with insulations or are they exposed wires.

Yes yes yes don;t touch the power lines, but what ? They are exposed ????

Ice Wolf
12-27-2002, 05:43 AM
Overhead power lines have no insulation and can carry more than 500,000 volts. If you touch one of these wires with your body or an object you are holding (such as a paint roller or ladder) while you are grounded, you will provide an instant path for electricity and will be hurt or even killed.


From this site. (http://we-energies.com/safety/electrical/power_lines.htm)

trader_of_shots
12-27-2002, 05:52 AM
Um...sorry stupid follow up question Ice..... Umm.. why don't they have insulation ?

If i was to hazard a guess i would say cos of the extra weight that the line would have to endure may cause breakages.... but then again could be $

Ice Wolf
12-27-2002, 06:17 AM
Not such a "stupid follow up question", trader_of_shots -- I dunno.

Some wires are insulated, some aren't. Could be to do with cost, use, resistance in the wires ...

There is a loosely related Straight Dope column (https://academicpursuits.us/mailbag/mbirdwire.html) about why birds don't get fried just sitting on the lines.

What may look like insulation on some lines is really just weather protective coating. Basic rule of thumb: don't touch, mate, or you'll end up as a crispy critter.

trader_of_shots
12-27-2002, 06:25 AM
Oh yeah can dig .. i am just curious now .. picked up a bit of info that says %90 of overhead lines are not insulated, and being the conspiracy freak that i am, i am tryign to work out what the goverment is hiding.

trader_of_shots
12-27-2002, 06:42 AM
Hmm bit more research indicates that the level of insulation (thickness) of polymers would be too great so it aint worth it.

Thoughts ?

Jdeforrest
12-27-2002, 07:25 AM
Nother quick questions. We all know it's not the volts that kill you, it's the amps. So does anyone know offhand how many amps do the power lines carry?

Ice Wolf
12-27-2002, 07:35 AM
Another source. (http://1stardrive.com/wildhorseacres/alturas.shtml) Don't know if itr's any help.


Typical house voltage is 120 volts. Typical current line is 20 amps. Typically house current feeds are 100 amps - 200 amps. Typically, the high voltage lines in the street are 15,000 volts. Typically, in an urban area, tower power transmission lines are 100,000 volts at 1000 amps. 150,000 volt line are really tricky. Birds land on them in the wrong place, there might not be much left of the bird. Lucky for birds, major power lines vibrate due to the massive current loads. Birds tend to shy off landing. Not always, it's a problem. 450,000 volts, the birds might not make it on the fly.

Una Persson
12-27-2002, 07:54 AM
Reasons they are not insulated:

1) Heat dissipation.
2) Weight.
3) Cost.
4) Lack of need.

casdave
12-27-2002, 08:01 AM
Strictly speaking it is neither the volts nor the amps that kill you.

It is the delivery of energy within a certain period of time, this is why you hear the actors on ER using the term "Joules" when using a heart defibrillator.

Joules is total energy, but when converted into a time dimension, this becomes Watts - Joules per second.

500KV and 1 amp is a huge amount of energy per second.

0.025amps can kill you given a supply voltage of 220V and bad luck.

Increase the voltage and you can use less current to kill, or conversely, decrease the voltage and it will take more current to kill.

Any voltage has to overcome the electrical resistance of the human body though, under 100V you would have to be incredibly unlucky to be killed directly by electricity.

Once the voltage gets above 1000V then you are getting into serious trouble, and at 500000V your chaces of survival are small, even if you don't get killed by the shock, the arc burns through your body are horrific injuries, these are among the worst injuries apart from total localised flesh carbonisation that you can get.

My next door neighbour works on 500KV power lines, whilst they are live, there are ways of doing this safely but the precautions are pretty awesome.

NardoPolo
12-27-2002, 09:40 AM
Originally posted by casdave
If you mean telephone poles then you'd be ok, but if you mean power poles, then you would still be ok if you were not touching anything else, or you were properly insulated.
The power line and the phone line that come into my house come off of the same pole. This is typical for Pennsylvania, even in residential areas, though I understand other areas have their power lines buried.

When you say "power pole", do you mean the high-tension electric lines that are very high and always sizzle and snap? Or do you mean any residential electric line?

I see the tree limbs touching the lines occasionally, with no effects. Even when wet. When a limb severs an electric line there are sparks, though.

Uncommon Sense
12-27-2002, 09:44 AM
Casdave - Is right as usual, but I shall add more

Amps are (more directly) what kill. The amps are the wild card, whereas the voltage stays the same, the amps change according to the resistance. The higher the volts the easier the amps will travel through your resistive body.

What causes the damage to your body is the following,

1. the amount of amps

2. the path the current takes

3. the length of time of exposure

The volts aren`t as important as the amps because the amps can get you at lower voltages.

A static shock carries thousands of volts but nearly 0 amps.
If conditions were right you could be killed by a 50 volt source at mere milliamps.

You can touch any live wire, if you don`t complete the circuit to ground or to another hot wire of a different phase, without injury.

High voltage lines are not insulated. Cost and the fact that they are way up there are the reasons.

High voltage lines are not designed to carry lots of amps. The voltages get converted by the user via transformers. Volts and amps are inversely proportional. As the transformer kicks the volts down the ampere potential goes up. In other words, a large amp load at the user end does not reflect much on the high voltage lines.

Whack-a-Mole
12-27-2002, 10:27 AM
Originally posted by casdave
Once the voltage gets above 1000V then you are getting into serious trouble, and at 500000V your chaces of survival are small...

I thought many Vandegraff Generators (http://amasci.com/emotor/vdg.html) could pump out 500,000 volts and aren't especially dangerous. Again I thought it was the near zero amperage that keeps users form getting fried.

casdave
12-27-2002, 10:58 AM
Whack-a-Mole

Did we mention anything about VdeG devices or were we talking about power lines ? ;)

The static on your nylon shirt is likely in the order of 1000V or more, but not too may folk are killed directly by it, though the fashion police might have to kill their social lives.

Ethilrist
12-27-2002, 11:13 AM
Don't touch downed power lines? Nuts. (scratches item off To Do list). So much for that new hobby.

UncleBill
12-27-2002, 11:28 AM
When I was a kid I had a friend whose father had no arms. He was a Safety guy at SC Electric and Gas. He taught safety classes. One day, he had been working in a cherry picker on a line, and for a reason he cannot understand, he took his gloves off and grabbed the line. Was not thinking. He had a mechanical claw on his right arm stub, but nothing on the left. Took them off at the shoulder.

It made a profound impact on me for safety consciousness.

engineer_comp_geek
12-27-2002, 12:15 PM
The reason that a van de graf generator or just plain static from your clothes isn't very harmful is that the electrical discharge is very high in frequency (which means it tends to travel along the surface instead of deep inside you) and very short in duration. A shock from a power line is much lower in frequency and has a lot more current behind it.

Electricity basically has two ways of killing you. The first is that it can interrupt your heartbeat. If someone is standing next to you with a portable defib then they can knock it back into a normal heartbeat, otherwise you're in serious trouble. The funny thing about your heartbeat is that it is fairly sensitive to getting thrown out of whack at 60 Hz. This is why shocks where the current goes across your chest are particularly hazerdous.

The second way electricity kills you is that it can cook you. One of the old science experiments that I've seen a lot of people use to demonstrate this is to stick a nail in either end of a hot dog, and attach regular 120 volt house current across the nails. The hot dog is nicely cooked in a fairly short amount of time. The electric chair and power lines are fatal mostly because of cooking rather than relying on screwing up your heartbeat. If a 120 volt line will cook a hot dog in 15 to 30 seconds, imagine what a 5,000 volt line can do to you in a fairly short amount of time.

Also keep in mind that higher voltages can arc farther than lower voltages. If the voltage is high enough the electricity can jump from the line to you long before you touch the wire.

By the way, in case anyone attempts to reproduce the old hot dog trick, people in the electrical business tend to call a power cord with exposed ends like that a "suicide cord" and for good reason. Be careful.


High voltage lines are not designed to carry lots of amps.


Depends on what you mean by "lots of amps." The total power through a transformer has to stay the same (you can't defy physics, and a transformer doesn't create energy). So, if you house is using 20 amps at 120 volts, it will be a mere 2 amps off of a 1200 volt line or 0.2 amps off of a 12 kV line. However, it's not just your current that's on the main distribution lines, but the current to every house in your neighborhood, the neighborhood down the road a few miles, and whatever else is fed by that main line. The total current capability of the wire depends on the thickness of the wire they use, but I'd expect it to be able to carry a few hundred amps with no problem.

By the way, the reason the voltages are pumped up so much is that the losses in the line are proportional to the current squared multiplied by the resistance of the wire, and as in the above example 0.2 squared is a much smaller number than 20 squared.

Uncommon Sense
12-27-2002, 01:52 PM
precisely

X~Slayer(ALE)
12-27-2002, 02:28 PM
at 100,000 volts at 1000 amps, powerlines cant use insulation because it would be too heavy and too thick to string out over the hundreds of miles. Thats why they put it way up there so no ordinary fool can get to it. (the special fools will always find the way)

Another factor is that transmitting that much power produces a static charge which tends to arc over any insulation that you might use. Men who work with these powerline always make sure they are properly grounded before even coming near those things.

as a safety advice, at 100,000 volts with 1000 amps, theres really no such thing as insulation.

Pablito
12-27-2002, 02:57 PM
semi-related story:

A couple days ago, we lost all our power for a few hours--putting a serious cramp in the plans of people who were cooking for christmas dinner--because the top 30' section of a pine tree had snapped off in some high wind and lay resting across the power lines (4200V x three) just in front of my office. Although the tree top was still suspended some 20' in the air, it immediately caught fire and burned for the next couple of hours until the utility service arrived to take it down.
It was a pretty impressive display.

David Simmons
12-27-2002, 11:47 PM
Originally posted by Ethilrist
Don't touch downed power lines? Nuts. (scratches item off To Do list). So much for that new hobby.

Not only don't touch it. If you are close to it, don't even point at it. If you get the chance, watch the History channel film on high voltage power lines.

The modern method of working on them is to do it from an insulated bucket, or put someone on the lines from a helicopter.

Since the bucket or the 'copter are at a different voltage from the line, even if not grounded, those voltages must be equalized before the lineman can touch the line to work on it. So when the bucket is about 6 to 8 ft. away, a long conductive probe that is connected to the bucket reaches out toward the line to clamp on. When it gets in the vicinity of a foot away from the line a spark as thick as the man's forearm jumps between line and probe before the clamp is applied to the line to make a firm connection.

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