sd80mac wrote: 1. NOT CORRECT! electric CAN jump at least 10 feet.
I was on project on I-490 in Chili. We were doing concrete pouring on bridge deck over Westshore. The concrete boom was about 10-15 ft away from high tension wire. The truck had 3 axiles and... you know how big these rubber tires.. 1 1/2 - 2 feet between ground and rim?? there were burn spot on the ground next to all tires. And the BONUS part is that concrete mix truck was next to the boom truck and is not physically contact to the boom truck. Probably a foot apart. the mixer driver and a construction worker were leaning on the mixer truck. The electric jumped to the mixer and knocked these 2 people down. I was the closest guy to these truck since I was the construction inspector at that time. I saw the flash between the boom truck and concrete mix truck.
I never said electricty cannot arc, but Your talking about two different situations. First off, how far an arc will go depends on voltage, weather, etc. There is no set standard for arcing.
As for the situation you are talking about, a Concrete pump boom is not insulated. And high volatge tranmission lines are usually in the range of 100 KV plus. The situation you are describing is nothing like being on a locomotive. In your situation, you had a metallic boom, not insulated come within arc distance of of LIVE tranmission lines. A concrete pump is not the same as a utility bucket truck purpose built to work around high voltage. The boom becoming an instant path to ground and wet concrete only added to the issue. The scenario you encountered is typical of accidental contact with tranmission lines. It happens on cranes alot as well. Those voltages are so high that rubber tires will not help you.
Again, in the situation we are discussing in this thread, it's a totally different situation since there is constant grounding. Your encounter with power lines is only relevant in this discussion in that it's about electricity, but it does not apply to train crews.
sd80mac wrote: 2. even through locomotive is off the ground and wheel aren't on the ground, the locomotive is STILL GROUNDED because it's sitting on the ground. I dont believe there is any conduction parts between locomotive and truck. I dont think u are going to get electrouded from touching locomtive...
Don't quite undertand what you are saying here, did you mean "even though the locomotive is on
the ground"? in the case of a derailment? If that is what you are saying, there is most certainly conduction between a locomotive and it's trucks. The locomotive frame is resting on the truck bolster with direct metal to metal contact. And you even have grounding wires from each traction motor going to the locomotive itself to make sure the trucks, traction motors and locomotive itself are all tied together to prevent anybody from being electrocuted. The instance i was talking about with being electrocuted by touching a derailed locomotive applies to ELECTRIC LOCOMOTIVES drawing power from a Catanary system. Not a diesel locomotive. In the situation with derailed electric loco's, the danger is very real. Just because a locomtive (or any power cable) is touching the ground does not imply it is grounded
. Why do you think grounding rods on electric panels are in many cases 6 feet long? That is to make sure it is a good earth ground. Mereley toching the surface of the ground is by no means assurance that you are safe. And rubber soled boots are no assurance either. Hundreds of people die from electrocution right through there boots to ground. Certain types of materials and soils are simply not great conductors. You derail (for example) an AEM-7 and put all 8 wheels on the ground but the pantograph is stuck in the catenary. You now have 25k looking for a passage to ground. You step off and happen to step on a tie plate on the rail. Your hand on the grab iron, your foot on the return, BOOM.
Aside from taking the AMT-2 Electric Safety program (required for anybody operating under the catenary on Amtrak) i also took an electric hazard class for fire/rescue operations and they explain this situation in detail with graphic demos. Think of a typical Electric locomotive, derailed, you have the very edge of 8 flanges being your only hopeful source of ground. Those surfaces may all be on dry wood ties or ballast. Neither is a great conductor. I would not want to bet my life that it was a reliable ground. As emergency responders, we are not to touch any electric train that is derailed untill power is shutoff.You are nuts to assume that something is safely grounded simply because it's on the ground.
Diesel Locomotives are different in that when you go to idle, in most cases your taking that lethal voltage away. When you derail, your going to idle. The voltages present at idle are not normally anything to worry about with arcing and a diesel locomotives power is self contained, it does not have to have a return path for the voltage.