OK, I'll show my ignorance. Are we talking about voltage looking for a path to ground, like jumping a gigantic spark plug gap , or is this induced electricity from moving a conductor through a magnetic field?
I'll say it's more like high voltage and high amperage current looking for ground in some instances, and in others, like flying in air preceding a storm it might be considered the other. If flying before a storm, you only tend to feel it if your lines are pointed in a certain direction, usually 90 degrees to the path of the system. In flying near high voltage power lines, I would say it's the other. Electricity follows the path of least resistance, correct? If you get close to that 50,000 volt line under the right conditions, you are the path of least resistance and if presented to it, then it will jump that gap. Touching it is obvious. The best example I ever saw of this was at work one evening. We had just installed a huge 8 unit double path web press, and had to install new 480 volt service to power it and some other support equipment, about 1200 amps worth if I'm remembering correctly. The power company hung two 600 amp transformers, and we always hired outside contractors for the heavy stuff, like running the heavy cable from the transformer to a large panel on the wall near the press. They ran large diameter conduit across the roof, and penetrated the roof with an elbow to connect to the panel. After that, we did all other installations off that panel. We tapped 400 amps off that to run to another panel to power up some other support equipment plus a 480 VAC air compressor. We finished the press, test ran everything, got the county to inspect everything and gave us a blessing to use it for production. After about a month, another worker called me out to the poles that the transformers were mounted on. They ran a copper ground wire down the pole to a grounding rod to establish the earth ground. It was just getting to be twilight and getting dark. I got out there , and saw little lightning bolts running off the copper cable across the ground, like something out of a horror movie!! I called my bosses immediately, and told the press crew to shut the press down, and once they washed it up a bit, I pulled the disconnect on it, then shut down all the other equipment running off those transformers. This pissed off the press room supervisor but I didn't care, and put lock out locks on everything so no one did anything stupid!! I had heard that there was a plastic molding company in the building at one time and they had some sort of equipment outside in that area. I guessed that what ever it was, something leeched into the ground and it wasn't a good earth ground any longer, but there had to be something else wrong with the main power installation. The vendor that installed the roof top portion was called, and they tested the ground around the poll, which I guess they did NOT do the first time. The shut off the main disconnect feeding the transformers, installed new ground cables that went out about 10 feet in another direction. They sent one of their guys back up on the roof to power it up, and there was an explosion and a shower of sparks!! Just like you see in "The Natural" when he hit the ball into the lights!! I figured we would have to call the fire department to come get a dead guy!! His boss yelled up to him," Are you OK?" and it seemed like forever before he answered " Uh, yeah! WTF happened??" I went back inside to see if anyone by the press failed to do what I told them, and that was stay WAY the hell away from the machine. As I got back by the big 1200amp panel, they were all looking up at the roof, and pointed to where they saw another shower of spark where the elbow penetrated the roof. It was burned black and welded to the roofing sheet metal. After some more investigation, it was determined that the vendor skinned the cable when they were pulling it through the conduit, and that point was right there at the elbow. The cable for things like this is huge, about the size of my thumb, and was either 500 or 750 MCM rated, and it doesn't bend easy so it takes specialized equipment to pull three lengths of that through the conduit, and it should be checked afterwards. The vendor didn't do that, and obviously didn't make sure there were no sharp edges or burrs in the conduit ends and the connectors. I personally ran hundreds of feet of conduit and miles of wire from that box doing other installations on the press and support equipment, after it was brought on line and hot. If that line had suddenly found ground while I had my hands on things, I wouldn't be typing this today!! I'll never forget seeing those little blue lightning bolt running off that ground cable "looking for ground." In thinking about it afterwards, I can't believe that no one got killed out of the event, including me!! There was so many ways that something could have gone wrong! The vendor had to replace all the cable and any damaged equipment from the event. The press couldn't run , nor any of the other 480 VAC equipment coming off that panel, and I imagine the company hit them for lost revenue for the two weeks or so it took to reinstall that line. it was the third or fourth time I was almost injured and/or killed following behind a licensed on the job. But I'm proud to state that of all the heavy equipment I installed and powered up, no one has ever had to follow behind me to correct anything or been injured by any of it. I learned everything on the job, and was taught by some really great guys that knew their stuff, learning from their experience and other peoples mistakes, and I'm still here with all my body parts because of it!!
Type at you later,
Dan McEntee
Topic: Why you never fly near power lines. (Read 2038 times)
