Wood FAIL

[eccentrictinkerer]

What happens when a branch falls on a power-line?

http://www.youtube.com/watch?v=DYktD...layer_embedded

[os1kne]

Neat - I didn't think that wood would conduct electricity. (I'm sure the voltage/amperage carried on those lines helps.)

[crokett]

'The branch might also be wet.

[cabinetman]

Power lines can be incredible. Next to my shop was a car repair shop that had a few cars out back. During a rainstorm and a lightning strike, a power line fell draped on a car, ran along the ground and over a dumpster.

The dumpster hummed, and turned reddish, and the car eventually started to burn, and all four tires blew. Fire department showed up, but could do little until the power company shut down the lines.
.

[phi1l]

Neat - I didn't think that wood would conduct electricity. (I'm sure the voltage/amperage carried on those lines helps.)

Sap will conduct..

[conwaygolfer]

Sap will conduct..

This is a fact. I used to climb trees for a living. One day I was using an old homelite saw up a maple tree. The plug wire was bad and it came in contact with a limb next to me. I was holding another limb several feet away. I started getting shocked thru the limb I was holding. The only thing I could figure, was the electricity went thru the one limb to the trunk and then back out the limb I was holding onto. Just glad I wasn't barefooted. It wasn't too long before I replaced the plug wire.

Conwaygolfer

[jackellis]

Looks like a three phase distribution circuit, probably 13,000 volts. Even a dry tree branch probably has enough moisture to conduct electricity at that potential.

All of the insulators on the poles are ceramic for a reason.

Some other pretty spectacular light shows" http://205.243.100.155/frames/longarc.htm

[LCHIEN]

all that screeching noise at the beginning was the moisture cooking out of the branch before it dried enough to catch on fire.

Interesting video.

[BobSch]

Since the fireworks didn't start until the fire had gone all the way across the branch maybe it was the carbon in the charred wood that conducted enough to allow the arc to form.

[jdon]

Since the fireworks didn't start until the fire had gone all the way across the branch maybe it was the carbon in the charred wood that conducted enough to allow the arc to form.

Not to quibble too much, but assuming that the branch was green wood, all of the electrical energy conducted across the branch is used to heat (and boil) all (or most) of the water in the branch (as LCHIEN referred to), and the temperature of the branch won't exceed the boiling point of water. That's the basis of the classic chem class demonstration, where a shallow pan made from stiff paper (like and index card) will not ignite when held over a flame, as long as is contains water.

What conducts the electricity is the movement of electrolytes (ions) dissolved in cell water- be it plant or animal. That's why EKGs and electric chairs work. Pure water is a very poor conductor, as are electrolytes in the absence of water (dry salt, for example, or dry wood). I suspect that the sequence- localized areas of flames before the final arcing- is due to the non-homogeneity of wood, with different rates of water loss, until the water was virtually entirely boiled off, allowing the temperature to rise dramatically at the end. Sorry for the rant- you can take the chemist out of the classroom, but....

In any case, an awesome video!

[conwaygolfer]

That's the basis of the classic chem class demonstration, where a shallow pan made from stiff paper (like and index card) will not ignite when held over a flame, as long as is contains water.

I guess that is why a boat only burns to the waterline. I once took a paper cup full of water and placed it in a fire while camping. The cup was fine as long as water was in it.

Conwaygolfer