Working Around Electricity

Brian,

Are you able to carry on a dialog? That means being able to listen to what others have to say without attacking or fuming. Just becaues everyone doesn't follow lock step in your thought pattern doesn't mean that you're being attacked.

Calm down and lighten up. Think of this as a pot luck. Is that just a Midwest thing maybe? When someone has a party, everyone who comes brings something to share. Rolls, drinks, a favorite dish, I make a dang good fruit salad that's pretty famous in my family. If there's something on the table that you don't like, the polite thing to do is just pass it up. Making nasty and rude comments on someone else's gift is considered very boorish. I've know people who got shuffled out of the party for doing that. Get my drift? Share a dish but don't be spittin' on my fruit salad. If you don't like it, keep it to yourself, I'm not holding a gun to your head to eat.

Now, where were we? Oh, electric lines...
 
Where we are joint use we refer to it as our space and their space.
Different voltages require different space.
The higher the voltage the more space is required.
It wouldn't hurt to develop a safe working space around live power where arborists are concerned just as a rule of thumb.
 
A utility forester with years of line clearance experience told me to treat service drops like big extension cords. That analogy has worked during my decade of tree work, including 3.5 years of line clearance. I wouldn't want to mess with a worn 110 volt extension cord any more than a worn 220 volt housedrop.

We have insulated 7200 volt primaries called tree wire here. It's rare, but exists.

I think all pole pruners used in tree work should have insulators on the cords. Even though working around the wires may be rare, might as well be prepared.
 
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Chris,

I agree here. The most important concept to remember is resistance. If you create a path of less resistance than that service drop, you will be energized. The easiest ways, like said before, water, dirt, grease... or cut the wire with your handsaw. I knew of a guy who cut into the service drop with the finish cut with his handsaw. He said that his chest hurt and then died. Rare, but can surely happen.


I've seen plenty of guys touch and even grab and move a service drop with no problems. It's all about resistance!

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A couple of points here--and considering our practical interests in staying alive:

Electricity doesn't take the path of least resistance. That's a never-properly-killed myth that is useless in the electrical business; disproven by every parallel circuit lesson in schools; and quite misleading in discussions here about safety.

Electricity takes every path it can. Whatever the resistance, the voltage will drop a proportional current flow across that resistance. If your hands are dry and calloused, that's one resistance. If they're sweaty and thin-skinned, it's a significantly different resistance.

What's critical issue here is how much current can flow through the chest area and the heart. Our heart beats are run by a very complex unrolling set of muscle instructions, each telling what spot and muscle to contract and expand. Hearts aren't flapper valves or switches, simple and foolproof; they are complicated pumps that need everything in place and in sequence. A disturbance of those instructions sends the area and the heart into a series of flutters--muscle movements that aren't coordinated and remain twitching.

It takes only 15 or so milliampres (15/1000's of an ampere) to disrupt the required patterns and there appears to be no body defense mechanisms available to come out of this mess. When this disturbance appears in the heart area, it is the RESULT of whatever circumstance that were present to allow that amount of current flow. None of us can predict it, so it makes sense to stay away from the circumstances.

I once fired a journeyman electrician for telling an apprentice he didn't need an electrical tester; just put his fingers on a circuit and the current would travel through one finger and out the other--he'd feel a tingle--no harm; no foul.

That will happen; electricity will take that route. But, it will also that the route from his fingers, up his arm, through his chest and down his legs to the wet floor. The victim gets one tingle and one disrupter. One tells him there's electricity preasent; the other tells his wife he's dead.

A really good way to stay alive is to understand electricity --and its crcumstances. A better way is to aggressively look for knowledge and skip the journeyman's macho-ignorance as a part of a karma. I am not disrespecting anyone or anything here, but erring on the sideof your own safety is prudent for you and the ones deopending on you. Be skeptical; ask good questions and look at sites about electrical safety as independent issues.

I'm just getting back in the saddle and haven't reviewed everything, but the prime directive here is to not let your body be a part of a current flow path. None of us are smart enough to do the math and know the answer (more than 15 ma.) before we touch something that might be energized.

Stay safe and tough.


Wulkowicz
 
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I'm just getting back in the saddle

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Ride em Cowboy! The range has been wasteland without ya; many coyotes, few wolves.

Fung brung dung, hung tongue.
 
Thanks for the insight. Very well thought out post. If I may ask, what is your background or job title? It sounds like you have had extensive training in electrical awareness. Are you a lineman? Or line-clearance arborist?

Not really a matter. What you say makes sense. I have one question in my mind though. Is there a difference in potential when talking about resistance? Can potential be stepped up if wet, greasy or dirty?
 
Some reading for the motivated...

"Ventricular fibrillation can be triggered by very small electrical stimuli. A current as low as 70 mA flowing from hand to hand across the chest, or 20µA directly through the heart may be sufficient. It is for this reason that most deaths from electric shock are attributable to the occurrence of ventricular fibrillation."

Here's an approximate set of figures for electrical resistance of human contact points under different conditions:

1) Wire touched by finger: 40,000 to 1,000,000 ohms dry, 4,000 to 15,000 ohms wet.

2) Wire held by hand: 15,000 to 50,000 ohms dry, 3,000 to 5,000 ohms wet.

3) Metal pliers held by hand: 5,000 to 10,000 ohms dry, 1,000 to 3,000 ohms wet.

4) Contact with palm of hand: 3,000 to 8,000 ohms dry, 1,000 to 2,000 ohms wet.

5) 1.5 inch metal pipe grasped by one hand: 1,000 to 3,000 ohms dry, 500 to 1,500 ohms wet.

6) 1.5 inch metal pipe grasped by two hands: 500 to 1,500 ohms dry, 250 to 750 ohms wet.

7) Hand immersed in conductive liquid: 200 to 500 ohms.

8) Foot immersed in conductive liquid: 100 to 300 ohms.

9) Anything in between, take a guess: 100 to 1,000,000 ohms.

"The conditions necessary to produce 1,000 ohms of body resistance don't have to be extreme...(sweaty skin with contact made on a gold ring). Body resistance may decrease with the application of voltage (especially if tetanus causes the victim to maintain a tighter grip on a conductor) so that with constant voltage, a shock may increase in severity after initial contact. What begins as a mild shock -- just enough to "freeze" a victim so they can't let go -- may escalate into something severe enough to kill them as their body resistance decreases and current correspondingly increases."

So the circumstances of contact will determine whether you live or die at 120vac = 170v peak to peak or 240vac = 340 v peak to peak. Obviously to get the 240vac shock you need to contact across both hot wires.

Any voltage above 30 is generally considered to be capable of delivering dangerous shock currents. At thousands of volts you simply fry, fibrillation is irrelevant.

How many of you have experienced tetanus? As kids we used to grab hold of electric fences for fun (double dares)./forum/images/graemlins/smilie_schreck.gif

Here are references:

See "Cardiac Effects" 1/2 way down---
http://web.bsu.edu/tti/3_3/3_3h.htm

http://www.osha.gov/SLTC/etools/construction/electrical_incidents/eleccurrent.html

http://www.bassengineering.com/E_Effect.htm

http://www.allaboutcircuits.com/vol_1/chpt_3/4.html
 
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What you say makes sense. I have one question in my mind though. Is there a difference in potential when talking about resistance? Can potential be stepped up if wet, greasy or dirty?

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Potential remains the same. Think of that massive nuke plant whose only job in life is to maintain a constant voltage at the load no matter what---downed line, whatever. Resistance usually decreases with wet, grease, and dirt (ions). So up goes the current through the load. I=V/R

Might be worth mentioning how voltage diminishes along a resistive path. It will never exceed the voltage that is at the source. Example is step potential. Another (maybe poor) example might be a wet climbing line with one end touching a wire at 120v and the other touching the ground at 0v. Midway along the line you'd be looking at 60v with respect to the ground. A tall guy footlocking might get a bigger jolt than a short guy. (If they had no gloves and were barefoot. /forum/images/graemlins/grin.gif)
 
Looks like I missed this the first time around. The only thing I will add to Bob and Chuck's comments is that if you need to work around electricity it is best to use only your right hand. This tends to keep the current from a shock away from your heart.

Cary
 
This is the best description of electricity that I have ever read. Last year I was reading Hunter S. Thompson's book on the plane to Expo in Long Beach where I was going to do an EHAP training. This is what I found:

Lock one hand behind your back before you touch anything full of dissatisfied voltage-even a failed light bulb-because you will almost certainly die soon if you don’t.

Electricity is neutral. It doesn’t want to kill you, but it will if you give it a chance. Electricity wants to go home, and to find a quick way to get there-and it will.

Electricity is always homesick. It is lonely. But it is always lazy. It is like a hillbilly with a shotgun and a jug of whiskey gone mad for revenge on some enemy-a fatal attraction, for sure-but he won’t go much out of his way to chase the bugger down if ambush looks a lot easier.

Why prowl around and make a spectacle of yourself when you can lay in wait under some darkened bridge and swill whiskey like a troll full of hate until your victim appears-drunk and careless and right on schedule-so close that you almost feel embarrassed about pulling the trigger.

That is how electricity likes to work. It has no feelings except loneliness, laziness, and a hatred of anything that acts like resistance…like a wharf rat with its back to the wall-it won’t fight unless it has to, but then it will fight to the death.

Electricity is the same way: it will kill anything that gets in its way once it sees a way to get home quick…

Zaaappp!

Right straight up your finger and through your heart and your chest cavity and down the other side.

Anything that gives an escape route. Anything-iron, water, water, flesh, ganglia-that will take it where it must go, with the efficiency of gravity or the imperative of salmon swimming upriver…And it wants the shortest route-which is not around a corner and through a muscle mass in the middle of your back, but it will go that way if it has to.

-Dr. Hunter S. Thompson
Songs of the Doomed
More notes on the death of the American Dream
Gonzo Papers Vol. 3
 
I recall from my power-plant days that when making boiler water the target was extremely low conductivity. This was achieved by removing (as practically as possible) everything that wasn't H or O.

Not that we'd encounter it in practice, but it's not the water itself that promotes circuit-making, but the stuff (salts/ions) attached to the molecules.

http://en.wikipedia.org/wiki/Electrical_conductivity and links within are "fun" (one link contains "while distilled water is almost an insulator, salt water is a very efficient electrical conductor" -- we all know which end of the spectrum sweat lies near!).

Dang! The local FOX station is replaying their 10 o'clock news and they just had a report that the Emerald Ash Borer was found just west of Indy. The trees which had been removed were no more than 3" or 4" DBH so I'm guessing the source was a nursery somewhere. They speculated the infestation could have been 7 years old...
 
"The wire does have a weathercoating which will insulate the wire as long as the weathercoating is not cracked or broken."

The idea that we might be SURE of being able to see any fault in the covering on a line is I think false.

"The secret is being informed and prepared if something happens out of the ordinary."

If your heart gets enough current to it there will be NO time to do ANYTHING. This does not mean one has to be scared, panicky or irrational in any way. It means the opposite. We need our best thinking and mental and physical control to have a safe working life around electricity.

A highly qualified electrical mate of mine says that the current can increase rapidly in some situations and there is NO reason to ever have any faith in things cutting out before it kills you.

Pete
 
A few thing I forgot to add yesterday. With the price of portable defibrillation machines becoming almost reasonable does it make sense to include them as part of the standard first aid kit? They may not help with the severe shocks, but they would help if your only problem was a stopped heart.

Second, like Glen mentioned about water it's the ions that cause the problems. The same applies to your skin. Clean and well rinsed dry skin will significantly reduce the level of shock you receive. Your core is conductive no matter what you do.

In general the shock potential of a house drop is no different than the 120V plug in the wall. You are at ground potential and the legs are each at 120V. It's only if you get really creative and get yourself connected between the two do you have a problem. Shorting the two out with a saw will create a 240V problem for the saw but only a 120V problem for you.

Cary
 
"Clean and well rinsed dry skin will significantly reduce the level of shock you receive."

Sweat or oil off a saw or other contaminants could appear RAPIDLY anytime on your skin. In an instant. Why think about all this in terms of things that MIGHT minimise conductivity instead of thinking of it by always working to the worst case? It's not that hard to work like that and it gives you practice in working well more often.

"only a 120V problem for you."

It's the CURRENT that kills you.
 
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... Why think about all this in terms of things that MIGHT minimise conductivity instead of thinking of it by always working to the worst case? ...

[/ QUOTE ]Point taken. I guess I like to try and add a little extra margin over and above what you get from just using best practices. I probably should add that pruning trees is not how I make/made my living so I get to work at a slower pace then most.

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It's the CURRENT that kills you.

[/ QUOTE ]That's certainly true, but current has at least a linear and more likely slightly non-linear relationship to voltage. My comment was more directed to Chuck's comments about residential 240V. Which in the US should not exhibit anymore shock potential than any single 120V leg. Oh and I have made a few dollars making electrons dance.

Cary
 
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It's only if you get really creative and get yourself connected between the two do you have a problem. Shorting the two out with a saw will create a 240V problem for the saw but only a 120V problem for you.

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I know exactly what you mean, Cary, but that could be construed to mean you'd think there wouldn't be a problem so long as you only got bit by one leg at a time.

Personally, I think one would be relatively safe if they could manage to snag the ground lead both first and last if they were sawing through the drop.

The stuff I've been working on lately, they get anal about having the bolts in the lugs attaching the conductors on either side of the breaker protrude away from each other to maximize the gap. And it's not uncommon to have to clean the insulators several times before getting good test results. 34.5 KV stuff is neat.
 
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I know exactly what you mean, Cary, but that could be construed to mean you'd think there wouldn't be a problem so long as you only got bit by one leg at a time.

[/ QUOTE ]Yikes! Did I type that! What I meant to type was you would only have a 240V problem if you got connected between the two. Otherwise it is the standard 120V problem. Which as we all know may or may not be a problem.

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Personally, I think one would be relatively safe if they could manage to snag the ground lead both first and last if they were sawing through the drop.

[/ QUOTE ]Wouldn't it be nice if you could make it happen that way. As I am sure you know many buried feeders are coaxial for just that reason.

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The stuff I've been working on lately, they get anal about having the bolts in the lugs attaching the conductors on either side of the breaker protrude away from each other to maximize the gap. And it's not uncommon to have to clean the insulators several times before getting good test results. 34.5 KV stuff is neat.

[/ QUOTE ]Sound like fun /forum/images/graemlins/grin.gif. I try to stay at 480V and lower.

Cary
 
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