Tuesday, November 30, 2010

June 26th, 2008

Portland, Oregon A Liebherr 100 struck power lines which electrified the crane but did not electrocute the operator. After the power was shutdown he climbed down  the crane with the Firefighters. Source

The pull on the loadline looks as though the operator was swinging the crane with an empty hook at a radius that was too far out and with the hook too low. A lapse of thinking while operating?

The crane was clearly grounded well since he isn't dead. Potentially there could be quite a bit of damage done to the crane even with proper grounding. The motors could end up burned out due to the immediate surge. The issue that stands out to me is the condition of the slewing bearing. Cross arcing between the balls is a known problem on cranes that have received multiple lightning strikes and it leads to premature deterioration of the bearings themselves. The Loadline is destroyed on this crane. While you might be able to pick up a small line like this for a few thousand dollars, you'll have to have it installed, potentially wait for it and what does shutting the job down really cost? All of these consequences assume that there is not a load on the hook and that no one is touching the crane itself.

This is where I speak of the virtues of modern cranes over even a 10-15 year old crane like the one in this case. Most modern cranes have the option of what Liebherr calls a ABB system. What it does is allows the crane to block out areas of operation. In a case like this, you would trolley out to the tip and swing out to the limit of operation (10 feet away from 50kV and add .4 inches of clearance for every kV above that), mark that spot then travel to the opposite point, mark it, and the crane will prevent the operator from swinging into that area. It knows the virtual location as a straight line, or you could set it up for multiple direction changes. Almost every crane manufactured since 2005 has this option, so if you are going to work with a tower crane near power, I cannot recommend this feature enough. I've had older operators balk at the idea, but I frankly don't understand it. It's like being against a seat belt or Anti-lock brakes. Unless you are in a race car, why is that again? If it's my insurance on the line, the system will be turned on when I'm there.

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