Why do the Tires blow on a crane truck when it has electrical contact with overhead lines?

Status
Not open for further replies.

nuckythompson

Member
Location
Nova Scotia
Occupation
Electrical
I thought the rubber tires would act as an insulator.. is it because there is steel inside the tires? I also would think the least resistance path would be the outriggers, which in this instance were directly touching the ground and not on wood blocks. Is there a ground under the hood for battery/ electronic connections? Thinking it could travel there as well.
 
Probably hard to answer without a lot more information.
Crane came within 10’ of 69kv line. It was a truck crane where the cab was on the back of a truck skid. It arced and triggered the substation recloser to trip. The arc went from line to top of crane. What other info do you need… ? One of the front tires of the truck went flat and had burn marks but so did the out riggers. Looked like little welding marks
 
Second question first: The entire truck body and chassis will become energized, but nothing would cause voltage gradients across components.

Probably a combination of arcing/carbon tracking and puncturing the rubber with voltage. There is likely to be current through the outriggers, too.
 
The tires will have some current flowing across them. Current takes all paths not just the ones with least resistance. There actually maybe quite a bit of carbon in the truck tires, as well as some moisture inside of the tire itself. An inch or so of rubber is probably good insulation for 480V but it will not be for 69kV.
 
Park that sucker on high moisture dirt or grass and anything possible. Also depending on height of the mast, the knee-jerk reaction and moving the mast quickly could break the beads on tires, regardless of outriggers... anybody know the osha distance for 69v+-?
Not 10'?!
Boneheads putting others in danger, bugs the heck outta me....
 
What I'd like to know, is why the operator was operating a crane with the tires touching the ground? For pretty much any crane manufactured in the last 70 years that is considered operating "off the chart"
 
Vehicle tires are deliberately conductive, to drain any static charge off the body when pulling up to a filling station. I assume crane tires are made in the same factories from the same raw materials.

Yeah, remember when tankers used to drag a chain. They stopped having to do that when they increased the lampblack

EhmIaF8UMAAhotq.jpg


In some parts of the world they still drag an anti-static strap
 
I think the conductivity of carbon black in tires is an ancillary benefit, I believe the primary reason it is used is the properties it gives the rubber.
 
I still want to know what kind of idiot was operating a boom truck with the tires touching the ground. No boom truck has an "On Rubber" chart. Any tire touching the ground even a little bit and you are off the chart. You are operating totally outside the manufacturers ratings.

NBT50-outriggers.jpg

boom on outriggers.jpg

We don't just lift the tires off the ground for fun
 
I still want to know what kind of idiot was operating a boom truck with the tires touching the ground. No boom truck has an "On Rubber" chart. Any tire touching the ground even a little bit and you are off the chart. You are operating totally outside the manufacturers ratings.

View attachment 2566323

View attachment 2566324

We don't just lift the tires off the ground for fun
Outriggers can burn too.
 
I still want to know what kind of idiot was operating a boom truck with the tires touching the ground. No boom truck has an "On Rubber" chart. Any tire touching the ground even a little bit and you are off the chart. You are operating totally outside the manufacturers ratings.

View attachment 2566323

View attachment 2566324

We don't just lift the tires off the ground for fun
There are a lot of small truck cranes that have plenty of boom to get into power lines that only use stablizers and not outriggers and the tires stay on the ground.
 
Outriggers can burn too.
Believe me I know, I lost family and friends in 2003 from a crane vs 13.2KV accident in Telford Pa. We cut the crane up for scrap because the idea of it still existing was freaking out the women. I saw the damage

I was just pointing out that the operator was unqualified, careless, sloppy, or whatever by operating with tires touching the ground. Big chance of upsetting the crane.
 
We were erecting a traffic signal pole with a street light arm and fixture attached. To aid in lining up the base of the pole with the anchor bolts in the foundation we loop a rope around the street light arm. On this occasion, the individual entrusted with holding the rope, let go of it as soon as the pole reached its vertical position. As a result, the poles base quickly moved towards the boom truck, a fellow worker was in its path. I immediately grabbed the pole into a bear hug eliminating the possible injury to said fellow worker. When I grabbed the pole I looked up to see the street light arm swing into the overhead Edison 40,000 volt lines. The operator of the boom, seeing what was happening, jumped off the boom and threw the rope around the pole allowing me to let go of it.

I hugged that pole for a few seconds, those seconds seemed like minutes. In those few seconds I noticed: The street light arm touching three of the four Edison lines, the top of the pole, inches away from the fourth wire, was arching to the fourth wire. The outriggers of the boom were melting the asphalt and sinking into the pavement. And most importantly, "I should be dead," I thought.

You can, to this day, (this happened 30 years ago) still see the marks the pole made on those wires. My boots saved my life.
 
Crane came within 10’ of 69kv line. It was a truck crane where the cab was on the back of a truck skid. It arced and triggered the substation recloser to trip. The arc went from line to top of crane. What other info do you need… ? One of the front tires of the truck went flat and had burn marks but so did the out riggers. Looked like little welding marks

Mostly voltage, but it looks like everything’s been pretty well covered.
 
Status
Not open for further replies.
Top