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#211609 - 11/20/10 01:25 AM Determining if downed power lines are live?
JohnN Offline
Old Hand

Registered: 10/10/01
Posts: 966
Loc: Seattle, WA

We had a windstorm a while back that downed a number of power lines. This made quite a maze of roads that were and were not blocked.

But, I could imagine if the storm had been a bit worse, that it could be much more difficult to travel without crossing some downed lines.

Is there any safe way to determine if a downed line is live or not?

-john

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#211611 - 11/20/10 02:10 AM Re: Determining if downed power lines are live? [Re: JohnN]
Susan Offline
Geezer

Registered: 01/21/04
Posts: 5163
Loc: W. WA
What's the emergency that you would consider driving over downed power lines? Turn around and go back to an open area and park. If you're headed home, tell Honey you'll be late. If you're going to work, tell them you'll be late or you're sick. If you're bleeding heavily or your labor contractions are less than two minutes apart, you shouldn't be driving, anyway.

If you insist on driving over live power lines, your car is wearing studded tires, and you survive, be sure to post here and tell what happened to the tires. I've always wondered what would happen.

But this looks like some good advice:

"If you must drive, be watchful for downed power lines, tree limbs, and general blockages in the road. Never drive over a downed line with your car. If the car has made contact, your car could become energized. Stay in your car and roll your window down to call for help. You can also use a cell phone to dial 911.

"... If the car has made contact and catches on fire, you have two problems. Donít panic! You must get out of the car in this instance. The way you exit the car will determine whether you live to tell about it. Open the carís door and stand on the floorboard of the car. Jump away from the vehicle with both feet together as far as possible. Donít hang on to any part of the car during the jump, including the door handle. If you do, youíll likely become the path to ground from the energized car to the street below. Remember, your car has four rubber wheels and is essentially insulated from the ground. When you just step out out the vehicle while touching it, you have completed the circuit.

"De-energized Power Lines - Although you can see that the power lines are down and the power is out, donít think that it is safe to move a downed line. These power lines could become re-energized at any time! Never assume anything when working around power lines. Instead, assume that they are live and that electrocution dangers exist."
From 'Downed Power Lines'

Sue

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#211619 - 11/20/10 03:27 AM Re: Determining if downed power lines are live? [Re: JohnN]
rebwa Offline
Enthusiast

Registered: 01/25/09
Posts: 295
I agree with Susan, there is no way that I would ever assume they were not live. A couple winters back one went down on the rural road I live on right in front of my place, I called 911 as it was obviously live and the fire department blocked the road until a crew got out here from the power company. I would think if the power company had already been there the lines wouldn't be on the road. Those things are nothing to mess with.

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#211620 - 11/20/10 03:27 AM Re: Determining if downed power lines are live? [Re: JohnN]
dougwalkabout Offline
Crazy Canuck
Carpal Tunnel

Registered: 02/03/07
Posts: 2741
Loc: Alberta, Canada
Downed power lines? That's serious business.

If you could visualize the amount of energy in a power line as a fire, you wouldn't even think about driving through it.

A tree took out the 15kV lines to my parents' place a couple of years ago. Even though they were both lying in a trout pond (the perfect earth ground, and no dead/boiled fish in evidence), I was not inclined to get close.

There are ways to detect voltage without contact, but in this scenario you could easily become part of the circuit before you could do the measurement. You can't help someone in distress by adding to the casualty count.

EDIT: To be fair, if I knew the line in question with a high degree of certainty, and had reliable evidence that it was de-energized, I might cross it if I had no other choice. An interruption in the overhead supply line past my house, for example, would be pretty obvious; the neighbours' yard lights would all be off. But in many other places, the line does not feed local residences directly, or at all.


Edited by dougwalkabout (11/20/10 03:38 AM)

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#211622 - 11/20/10 03:50 AM Re: Determining if downed power lines are live? [Re: Susan]
Desperado Offline
Veteran

Registered: 11/01/08
Posts: 1530
Loc: DFW, Texas
Originally Posted By: Susan
Remember, your car has four rubber wheels and is essentially insulated from the ground. When you just step out out the vehicle while touching it, you have completed the circuit.


Generally, above 7.5 KV, the tires last about 30 seconds. The next step following to four loud " POP's " is dark black smoke from your tires and you corpse.


We once had a lineman make unintended contact with 30KVa. He lost track of the lines and hit one with the arm of his aerial lift truck. It was not enough of a short to ground to cause the circuit breakers in the substation to trip, so he rode the lightning until the local utility dropped the power.

By that time he and the truck had completely burned to ash.

Keep in mind, within 4 feet of typical electrical transmission lines, the power can and will jump to the best path to ground.

DO NOT SCREW WITH DOWNED LINES.
_________________________
I do the things that I must, and really regret, are unfortunately necessary.

RIP OBG

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#211625 - 11/20/10 04:24 AM Re: Determining if downed power lines are live? [Re: JohnN]
dweste Offline
Pooh-Bah

Registered: 02/16/08
Posts: 2463
Loc: Central California
Knowing the downed lines might be live or become live at any time, it would take a rapidly approaching and imminent threat of death to force a conservative, survival type to choose a close encounter with them. But what if there was such threat of death? How then would you proceed?

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#211626 - 11/20/10 05:02 AM Re: Determining if downed power lines are live? [Re: dweste]
Richlacal Offline
Old Hand

Registered: 02/11/10
Posts: 778
Loc: Los Angeles, CA
If the Ground is Wet,Where the line/s have fallen,Stay Far away from it,Period!If someone is Stranded Between Powerlines,& Power co. or Help is 4hrs.Away or something like that,Lots of Dirt, Shoveled over a Line with Planks on Top,Would probably suffice, for a Rescue of The Stranded Person, But Only if it isn't raining/snowing!Note:There are Seperation Switchs to cut power on Power Lines,Usually Located on Power poles,& Usually 10-15' High,& Locked as well,But It could be done,If you cut the lock! This would work for an Imminent Threat Scenario! The Big Huge Metal Towers with The High Voltage Lines,I don't have a Clue,Short of a helo-lift!

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#211628 - 11/20/10 05:36 AM Re: Determining if downed power lines are live? [Re: Richlacal]
dougwalkabout Offline
Crazy Canuck
Carpal Tunnel

Registered: 02/03/07
Posts: 2741
Loc: Alberta, Canada
Originally Posted By: Richlacal
If the Ground is Wet,Where the line/s have fallen,Stay Far away from it,Period!If someone is Stranded Between Powerlines,& Power co. or Help is 4hrs.Away or something like that,Lots of Dirt, Shoveled over a Line with Planks on Top,Would probably suffice, for a Rescue of The Stranded Person,


With all respect, I have major problems with this advice.

For 220V yard wiring, it would work. But with live wires in the kilovolt range, all sorts of materials that would normally be insulators become conductors. This includes dry wood and soil.

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#211629 - 11/20/10 06:46 AM Re: Determining if downed power lines are live? [Re: dougwalkabout]
Richlacal Offline
Old Hand

Registered: 02/11/10
Posts: 778
Loc: Los Angeles, CA
Dry wood/soil ARE Not Conductors for Any Voltage,However with The Mega-Amps Powering Kilovolt lines,They aren't much of an Insulator,In that regard,That's For Sure!You Excluded what I had to say,Below that!Also It's Not Advice,It's a Suggestion for A Haste Scenario,ie. What is Immediately at Hand to Help.Either you Help,or You stand there doing Nothing,Your Choice!

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#211642 - 11/20/10 06:35 PM Re: Determining if downed power lines are live? [Re: JohnN]
JohnN Offline
Old Hand

Registered: 10/10/01
Posts: 966
Loc: Seattle, WA
A couple of things. In an urban area with a lot of trees, you could become boxed in with downed lines.

In a serious region wide storm, I could imagine help could be several days away.

Second, there are induction testers for home voltages, I can't imagine it wouldn't be possible to detect without actually touching the line.

What are the procedures used by linemen? It seems to me the would double check lines before working on them -- and possible safety measures like grounding to earth.

What are the real working parameters for safety? Is there a possibility of arcing, or is avoiding direct contact adequite?

Are the lines insulated, or no?

-john

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