overhead crane experiencing an arc

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jflynn

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Hello-we have a customer that is currently starting a project and is telling us that when his crane goes to pick a piece of steel-column or bar joist-they are experiencing quite a arc between the crane hook and any steel it goes to erect,-

They claim the power co has been on site and has verified there are no issues on there end-the area of work is in a pretty wide open area-there is an adjacent building that powers some site lighting-mostly overhead wooden poles that have aerial(looks like tri-plex)l cables between them-they do eventually end up going back to the adjacent building via underground thru one of the site poles for the buildings parking lot.-277volt.These poles are not in the area the crane is actually working-they are right next to it.

They are experiencing these issues during the day when the site lighting is de-energized- we have not seen the arc-but they claim it is pretty distinct and noticeable.

The job is near Boston ma-you can see Boston ed power plant and the MBTA trolley system are within site of the parking lot where this is happening.

ANY IDEAS?
 
A picture of the arc would be great!

If there aren't any circuits that trip when the arc happens, you may have static discharge that is being induced on the crane from nearby MV cables. I'd check the crane grounds and whatever the crane is ground to. Could be a bad ground mat. Also, what voltage is the crane?
 
Bugman1400 said:
A picture of the arc would be great!

If there aren't any circuits that trip when the arc happens, you may have static discharge that is being induced on the crane from nearby MV cables. I'd check the crane grounds and whatever the crane is ground to. Could be a bad ground mat. Also, what voltage is the crane?
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no circuits are tripping that we have been notified about-not sure the crane has any grounds- it is diesel fuel powered.
 
jflynn said:
no circuits are tripping that we have been notified about-not sure the crane has any grounds- it is diesel fuel powered.
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Regardless, of how the structure is powered, seems like it would need grounds on the structure to dissipate any static charge that may build up or from a lightning strike.
 
Bugman1400 said:
Regardless, of how the structure is powered, seems like it would need grounds on the structure to dissipate any static charge that may build up or from a lightning strike.
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How do you ground a mobile structure?

How would static build up on a structure with metal tracks sitting on the ground?

It takes very little to drain off static.
 
iwire said:
How do you ground a mobile structure?

How would static build up on a structure with metal tracks sitting on the ground?

It takes very little to drain off static.
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I did not pick up on that it was a mobile crane with tracks. I was thinking of the type for building high rise structures.....my bad.

For the arc to occur, either the crane is energized or the structure steel is. I would probably experiment with a clamp-on ground and see if the arc stops or is mitigated. Some of the large cranes may rotate to pick up and drop the load but, may not move too much because of the outriggers. Perhaps you could put the clamp there.
 
Iwire,

If you mean electrically-powered portable-machines or structures, then several methods are available:

o For small machines the grounding-conductor is in the power cable tethered to the machine or the drum-reel!

o For large machines the grounding-conductor is in the drag or trailing-cable!

o For very large or HV machine, or frame-to-ground resistance is high (even with ground-rods) then, a resistance-grounded system is employed!


In my own experience I never consudered metal wheel-to-rail, as acceptable!

Regards, Phil
 
Phil. We were taking about static charge and for that steel tracks would do it

As far as a spool and a wire that is highly impractical in most all cases unless you are talking about an electrically powerd machine as some mine equipment.
 
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