Overhead Powerlines

I have been watching the harvest in my area and my attention has been drawn to the size of today's combines v/s the distance between the top of the machine to the power line. We have all been coached to stay a minimum distance away from a power line as there can be an electrical arch that will jump a distance. The distance is unclear to me right now, but believe it is at least 6 feet. I see numerous instances of combines traveling under power lines that are within 3 feet of the power line! I realize the machine is on rubber, but....what if the operator parked under the line for whatever reason and climbed down the ladder to the ground. Isn't there a potential to be electrocuted when your foot touches the ground? I have never heard or read of this happening.....but seems like it could. Educate me please.

I've seen it happen with a dump trailer.The driver knew what he was doing,he was dumping on a project for an industrial park under some high tension lines.He was a lot more than six feet from them,and dumped with no problem.He called me on the radio,(I was the mechanic)and told me to get a tire ready because he had just blown one.i was headed for the tire shed when he called back and said he lost another one.OK,not unusual to lose the mate to it when one blows and the mate takes all the weight.It wasn't the mate.Then the boss got on the radio and asked him if he was near the power lines when he dumped.He was,the boss said get out a set of tires and some bearings.He knew exactly what happened.It was VERY hot and humid that day,and the current jumping through the tires has turned the steel cords into hot wires like in a toaster.When he ran the four miles back to the shop he had three tires out of eight still holding air.I didn't think such a thing could happen,but all the older drivers that had paved with dump trailers had all experienced it.

It takes a dramatic voltage to jump an inch. (in the area of 15,000 volts in dry air) Think of a spark plug wire to block distance. Most coils can make 20,000 and jump inside the cap at about 1/2 inch from the block. Once an arc is started the air, and exploded metal particles from the conductors create an ionized path that sustains the arc for far more distance than needed to start it. Most intermediate power lines carry between 3000 and 6000 volts AC (which is much higher peak voltage than that) ~6000 volts AC has a peak voltage of ~8555. So in reality clearing local lines that are allowed to be at ~16 feet above the road surface are pretty safe unless hit. Don't go there though, there be dragons. Jim
Calculator for arc gap

That is way too close to high voltage transmission lines, you can look up tables for safe distances and voltage. We have 115,000 volt lines here and they recently installed another pair of poles to raise up a span that used to hang a bit low during the warmer months. I would avoid crossing under them in hot weather, just not worth it and though it seemed there was just enough distance, high or any kind of voltage for that matter is not worth taking any chances. I could get a blue arc to span my finger tip to trigger guard on my rifle if I lifted the rifle up a bit and pointed the muzzle at the lines. With the span raised much higher I can still get an arc and hear it, but it is not as pronounced.

When they work around these lines with heavy equipment, they clamp off securely a ground cable to an earth ground.

Sprayers are the danger. Up to 120 foot span, they pull off the road and unfold on the edge of the field, which is often under power lines. Some unfold kinda vertical, can be a mast very high.

Paul

In "theory" you should be safe if you are as far away as the length of the insulator, if you are as far away as the gap between the lines then safe.

There are NEC rules that supersede my statements.

Here is OSHA views

They are super cautious.
OSHA

It is a chart which gives voltages and distances. I have it inside my hard hat in sticker form. Must know info.

Don't let the idea of being on rubber tires is going to help one tiny little bit. My buddy's kid was plowing a field that had a the one high voltage like 7600 volts running in it and it jumped from the line to the muffler about three feet . When this happened it blew every shear off the plow took out all five tires trashed out every bearing in the tractor whipped out the engine as it arched the crank and bearings and one pair of shorts and sounded like a 155 going off . Getting under them high tension lines can give you and education also , case in point here the sale lot at Tri Green in London Ohio .Years back my one buddy that he and i travelled to sales together went down to a March sale it was misty and cold when Donny and i got there Early and he and i were scouting the lot for some of our stuff that got moved and see what else was there so we could work out our game plan . He saw his piece of equipment and got out to look as the tag was not wright and it was setting under one of the towers , he was driving that day and we had his S 15 , Donny is shorter then i am and i am scrunched up in the passenger side , he jumps out and the wind blows the door closed so he finds his tag placed out of site and moves it so it can be seen . He grabs the door handle and is promptly knocked to the ground by and electrical shock . The power lines over head are sizzling and creating a static charge , now now being to bright he gets up and trys again to open the door and gets Zapped . I had to unfold myself and climb over all the junk we had inside to get behind the wheel and move the truck up from under the power lines , that day you could not touch anything setting under or around the towers with out getting zapped big time.

There was a low voltage line that went across one of my fields. At one point there was not adequate clearance for my bale wagons, so I had to detour around. I was spreading lime there last week for my friend who does it now, and I could see that they had raised it but probably only three feet.

Not exactly to the point, but I was on a job site with a smaller (40 foot) crane on a flat bed truck. They had made a BIG deal about staying clear of the power lines by the street (they said at least 4 foot away, if memory serves) and at first he did just fine. These were the 15 foot poles you commonly see in town. Next thing I know he had completely touched it, no one was hurt fortunately, but they said they were going to have to replace ALL the cable as it was all compromised!

You better bet sparkey!! Many years ago up near Allentown,Pa I stopped at a motel for the night. Was a very fine misty slight fog night. As I stepped out of my van I got a pretty good ZAP. Was parked under the big hi tenson line tower. It took out my meter and stuck one end in the ground and held the other to the door hinge. I was reading about 350 volt AC on the meter. Wished that there was a four foot neon tube in the truck so I could hold it up and light up the parking lot.

I was stationed North of the Washington State / Canadian Borden in the small town of Savona Canada. That area, is an area of high yielding crops of hay land due to high ambient temperatures and availability of inexpensive water for IRRIGATION.

Two young teenagers were horsing around, seeing how many lengths of aluminium irrigation pipe they could stand on end.

When the irrigation pipes came in contact with an over head high voltage power line, one young fellow lost his three middle fingers on his left hand immediately!

Very tragic day .


Bob...

Look at the distance between the 2 power lines which are what maybe 6 foot. Lower one is the ground and the higher one is the power and on the common lines it is around 7300 volts. I once worked on a insulation checker for the Bagnell dam power plant here at the Lake of the Ozarks. It put out 100,000 volts and when we fired it up we did so from across the room. and used a long extension cord to do so. Arch from it was around 6 foot between the 2 probes. But even 20 feet away form it you could feel the voltage in the air and the guy who plugged it in unplugged it pretty fast

My wife and I winter in Arizona. When we arrived back at our summer residence, the neighbor commented the Electrical Grid had "BLINKED" a couple of times while we were gone...?

The public utilities had ran their Power Lines down the center of our property back in 1963....one mile..
With the winter storms....the lines was on the ground. Several Deer had walked on the packed snow....the rest is self explanatory.

Bob..

The power plant I retired from this Nov has high voltage lines going out from it. The small units were 115kv and the large units were 250kv. We were always told 10 feet minumun on the 115kv lines. They were moving some top soil around one year where they were doing some construction. One of the contractor dump trucks left his box up and came to near the 115kv line, the line is quite high, probably 30 plus feet, the line arc jumped to the tandum dump truck and blew all ten tires and did a lot of damage to the trucks electrical system. The driver jumped clear and was un-hurt. It tripped the generating unit off line. When I was in operations we had to do some switching in the tranformer yard at times. big knife switch and a fibre glass pole, heavy rubber gloves and ppe suit. the arc that fallowed the knife till it gets a distance away will make the hair on your coved head stand up. :shock: Electrical power lines are not to be taken for granted and should be treated with caution.

Good day Lumbersawyer.......May I ask what make of Prime movers your plant used to drive the Generators?

In last three years of my 40 year carrier with a Natural Gas Pipeline Company, we installed 5 Meg Turbines at several of the Natural Gas Compressor stations.

The waste heat from the Exhaust stack from the 25,000 HP General Electric LM2500 Gas Turbine (Air Craft derivative CF8) was directed into a boiler. The boiler Tubes were filed with a synthetic oil that assumed the heat from the turbines.

The heat carrying medium from the boilers flowed through heat exchangers. This heat was transferred to PENTANE. The pentane flashed off into a vapour and drove a Reactive Turbine attached to the Electrical Generator.

Once the cycles, voltage, etc,etc, were parallel with the public power Grid the main breakers would lock in

5 Megs. is very small compared to most industrial generating plants.

Bob..Retired and loving it......

Wow I must have been lucky, when I was a teenager I had a favorite place to park with my girl friend it happened to be under high tension power lines, I remember hearing them buzz.

Doubt that line was 7,600 volts. May be more like 765,000 volts.

Yummy...venison steaks, nicely cooked to perfection. In an industrial park along the street somebody hit a pole. Kinda cool to watch a power line burning a trench into the sidewalk. Makes funky looking green glass paperweights.

By the way...I found out what all of the helicopter action down near Atlantic City is all about. They are putting in a new main power line and are using welded aluminum towers. They look right out of HG Wells War of the Worlds. Here is that big Sky Crane today. Boy that baby is big.

We had a chopper exactly like that this year lifting a Stainless steel extension ring on our #4 stack, it is 650 foot high and 35' in dia up at the top.

It is a coal fired station #4 unit is 630 megawatt and unit 3 is 410 megawatt. I worked on U4 as lead maintenance. The boiler runs at ~2600psi throttle pressure. Something like 3,800,000 HP The steam turbine/generator is 120' long and the low pressure blades are about 8' diameter and run at 3600 rpm.

Great place to work and now retire from. We provide electricity to the iron minning and paper industries.

I worked as a mechanic for a company that did high line work. Rubber tires will not insulate the truck. I've seen bucket trucks which the booms are insulated with all tires blown out. Only one of ours but, when this happens at one company usually every company gets a report and a picture for safety reasons. Also, a completely dead disconnected line can kill a person. One of our guys died when they were pulling and spooling a dead line. There was no way this line could have touched anything live. A foreman didn't have his safety equipment on. He grabbed the wire to help it spool straight. He never knew what hit him. It was windy that day. Wind going past that line caused a static charge. This is a true story. Stay away from any power lines live or dead!!!!!

Thanks Jim. Interesting stuff to say the least.

Thanks all for the input. Seems to me.....stay the heck away from them....period.

The guy plowing with a tractor with rubber tires is not going to be protected when the plow bottoms are in the ground....