Update: Wire fire on Hudson

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1:11 PM UPDATE: WSB contributing photographer Christopher Boffoli got to the scene on Hudson west of 42nd first (and photographed part of the actual fire, as seen above and below) and reports:

Engine 32 and Ladder 11 are on the scene and a bunch of firefighters are watching the wires burn. Even they were scratching their heads about how weird it is. One firefighter told me that when they rolled up, a length of wire a block long was on fire. For some reason the wires are so hot that the insulation is burning off. They said there is nothing they can do but to let the insulation burn out. (You obviously cannot douse the wires with water). They said that afterward they have to watch them because the fire can weaken the metal and they can fatigue and come down.

ORIGINAL POST AT 12:46 PM: “Wires down” — That’s the label for a fire call happening right now in the 5000 block of 42nd. Heard some scanner talk about possibly restricting some access in the area; off to investigate. 12:59 PM UPDATE: Hudson blocked west of 42nd. Two engines on scene, including the one shown below:

Cheryl December 17, 2007 (2:45 pm)

There must be too many Christmas light on that block. :)

Dis December 17, 2007 (2:46 pm)

wow! amazing photos.

miws December 17, 2007 (3:06 pm)

I wonder if that’s the same circumstances that happened here in the Morgan Junction area maybe 1 1/2-2 years ago. The power was out for a few hours, (which seemed like a long time until a year ago!) due to a wire fire.

The reasoning I had heard behind it, at least in that case, I think weather may have been dry for quite awhile, and the tempurature had fluctuated some, getting rather hot at times, causing the wires to expand and contract, resulting in the insulation cracking.

Then, we got a significant rain, and all the little bitty pieces of dirt washed into the wire itself causing shorting out and fire.

Though on one hand it’s dangerous and quite scary, it would be kinda fascinating to see it happen after dark. (In somebody else’s neighborhood! :p )

Mike

Jan December 17, 2007 (3:28 pm)

ok…my mind must be in the gutter…I was thinking it was a phone line….some hot conversations going on – lol……

Christopher Boffoli December 17, 2007 (3:50 pm)

I was thinking someone on the block might have just launched a basement marijuana grow operation and was using an excess of juice! As I was standing there I could just see the shimmer of heat humming off those wires.

Bob December 17, 2007 (6:46 pm)

The usual reason for car fuses getting hot enough to melt the metal inside them isn’t too much current flow but instead a buildup of corrosion on the fuse holder contacts holding the ends of the fuse. As a corrosion layer builds up around the contacting electrical joints, it slowly increases the contact area’s electrical resistance, eventually to something on the order of that of a toaster heating element instead of a fuse. At that point, the high thermal conductivity of the fuse means that the entire fuse is at a high enough temperature to melt the fusible tin alloy in the middle of it.

Something like this might have happened at the connections at one or both ends of this length of wire. Copper is an even better thermal conductor than anything in a fuse, and the thick insulation layer provides a good thermal insulation blanket as well as electrical insulation, under which the copper can heat up much more than if it were bare wire. The insulation’s burning point is probably a lot less than the melting point of fusible metal, as well.

Aidan Hadley December 17, 2007 (7:22 pm)

Bob: Automotive DC wiring systems and fuses have little in common with high-voltage AC residential delivery cables. Today’s fire could have been caused by the failure of a transformer which overloaded that section of wire. Or it could have been something as simple as damaged or degraded insulation that caused overheating or arcing of the electrical current.

Cruiser December 17, 2007 (7:44 pm)

Those bloody squirrels not putting out their cigarettes again:)

Bob December 17, 2007 (8:03 pm)

Aidan – Yes, they have almost everything in common that’s essential here. Ohm’s Law is equally true of steady DC and sine wave AC as well as other more complex waveforms. Anything other than DC computations does need to use RMS (root mean square) arithmetic, but the laws of physics that we’re concerned with here are the same regardless of the shape of the waveform. I might be wrong about what caused that section of wire to overheat. But Ohm was right all those years ago, no matter what you say about the “little in common” between conductors carrying AC and DC.

Cruiser December 17, 2007 (8:16 pm)

Still say it was the squirrels

MargL December 17, 2007 (8:22 pm)

I second the squirrel vote. I always blame them for static on the telephone line, too.

Aidan Hadley December 17, 2007 (9:11 pm)

Well Bob, it looks like you’ve managed to figure out how to do a cursory Google search, unless you copied all of that from a book. But what you’ve done less successfully is sound coherent. Before you go off throwing around words and terms you clearly don’t really understand, please keep in mind that the other nice people here in the comments section are strangers to you so it is not so important to work so hard to save face and sound right. Besides, I think the majority opinion seems to be that those pesky squirrels are to blame.

Jan December 17, 2007 (9:28 pm)

squirrels having hot phone sex ;-)

chas redmond December 17, 2007 (9:39 pm)

It sort of reminds me of some TV ad (or was it an internet ad) where the subject of the conversation was so hot that fire raced along the wire from the person talking to the person listening. I don’t buy the squirrel theory – I think Jan is right, it was plain and simple a hot and fiery exchange. So hot that it leaked from the phone lines to the power lines. Wonder what the next stage would have been? (shades of Stephen King here.)

Lisa December 17, 2007 (9:44 pm)

Last Summer our power went out for a few hours. I went to investigate what the power crew had to say about the reason for the outage and they pointed to the barbequed squirrel on the ground.

Bob December 17, 2007 (10:59 pm)

Aidan, when I was a younger fellow I was a field engineer and made a living troubleshooting electromechanical, electronic and eventually software factory control systems (well, after they invented software) out in the real world for many years. More to the point, one day a few years ago I looked at a family member’s new 120v electric heater that had gone out. It gave off a burning smell. Inside, some black ashy residue that used to be insulation surrounded the point where one of the 120v wires had been connected. It was basically what I described above. The contractor hadn’t soldered the wire in place but simply placed it in physical contact with a brass connector. The heavy gauge wire carried a lot of current, and before long the much higher than normal resistance of that connection caused enough heating to burn off the insulation in both directions away from the connector. Back in my shop, after soldering the wire in place (along with a second identical connector that hadn’t overheated as much but had been assembled the same way and also caused some charring) it measured much less than 100 milliohms resistance on my bench meter, not enough to ever heat up unduly again. Needless to say, the sloppy contractor never got any more such installation work from us.

Dis December 18, 2007 (12:50 am)

very classy response, Bob. It’s a good reminder for me that it’s never necessary to stoop; something I always need to remember.

Jaime Gummer December 18, 2007 (10:53 am)

Dis: There’s no need to “stoop” when you’re so busy spinning yarns. :-)

I have an ECE degree from Rensselaer Polytech (’96) and even I thought Bob’s car fuse story and penchant for ohms dropping seemed oblique. And while we’re on the subject, why is everyone so down on those cute little squirrels? I didn’t see any squirrels in those pictures of the wires on fire. Unless maybe there was a squirrel hidden on the grassy knoll.

JumboJim December 18, 2007 (12:16 pm)

I wouldn’t be surprised if it was a case of degraded insulation as others have suggested.

Just look around your neighborhood and I bet you’ll see some wires that look like the insulation has been caracking and falling off for quite a while

Jan December 18, 2007 (1:12 pm)

JJ…I like the squirrel phone sex explanation better…not quite so boring and technical ;-)

JumboJim December 18, 2007 (1:43 pm)

Jan – I didn’t say *why* so many lines have cracked and degraded insulation – I thought it was clear that it was because of overuse by randy squirrels. Why do you think there are so many squirrels?? ;-)

Jan December 18, 2007 (2:31 pm)

lol….

Bob December 18, 2007 (10:37 pm)

Well, be as skeptical as you like about poor connections overheating and causing fires. But this seems to have happened again this morning in an underground electrical vault north of downtown. City Light blamed the fire that led to the explosion on a bad splice and old insulation. What does a “bad” splice mean? High resistance, enough to cause overheating. Under some conditions, connections can corrode and gradually develop more and more resistance, becoming essentially a heating element. A conductor carrying 100 amps and that has a 1 ohm resistance at a bad, aging connection point will dissipate (current squared x resistance) 10 kilowatts in that resistance at that point. That’s about six 1500-watt four-slice toasters’ worth of heating applied to the bad connection point. Go ahead and disbelieve it if it suits you.

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