Free Standing Bridge Crane Lightning, grounding and bonding

[bilwei]

I have an Industrial client with two large free standing bridge cranes. These bridge cranes are outdoors. They are approximately 700' length, x 70' width x 55' height. They are experiencing VFD and other electrical component failure due to lightning strikes. They were built in the early 1970. There have been upgrades with the VFDs and other electrical components thru the years. However, they have not installed a 4th bus for an equipment ground as required by the NEC. Besides the 4th equipment ground bus issue, I cannot find any sort of lightning, grounding or bonding system protection on the structure. With the exception of the equipment ground (#4 awg) brought in with the power feeder to the service disconnect and mounted on the structure. I need some information (literature, published standards, etc.) for my knowledge base and to best advise my client on actions that need to be resolved immediately with respect to lightning, grounding and bonding.

The only way the structure is earthed is through the vertical supports, which are supported on concrete pilings.

In this situation, there are some dangerous touch potential electrical hazards not to mention the problems noted above.

 

[SceneryDriver]

I'd imagine that the concrete pilings are acting as pretty effective ufer grounds and tying the steel structure to earth potential.

Perhaps I misunderstood; is this crane on tracks? Could the steel wheels on the steel rails act as a grounding means? Probably not code compliant, but conductive nonetheless.

As for lightning strikes, lightning has its own agenda and will go where it wants to. Strike damage mitigation is an art unto itself.



SceneryDriver

 

[bilwei]

I'd imagine that the concrete pilings are acting as pretty effective ufer grounds and tying the steel structure to earth potential.

Perhaps I misunderstood; is this crane on tracks? Could the steel wheels on the steel rails act as a grounding means? Probably not code compliant, but conductive nonetheless.

As for lightning strikes, lightning has its own agenda and will go where it wants to. Strike damage mitigation is an art unto itself.



SceneryDriver

Thanks for your response. The crane is on steel tracks with steel rails.

bilwei

 

[mgookin]

If I understand this correctly, you have a 700' long railroad track with a 70' wide crane on it that's 55' high and of undisclosed length. The crane rides along the track back and forth.


Am I right so far?

 

[bilwei]

That is correct. In years past before the age of VFD, microprocessors and the fourth EGC bus, the steel rail and steel wheels were sufficient as the equipment ground. In my humble opinion, the bearings on the steel wheels are one of the week points. I have contacted Bonded lightning protection Co. for their advice and see if they have any experience in this situation. At one time my client had another bridge crane as a back up, it has been removed. Therefore, the one bridge crane is critical. It feeds the raw product into the plant.

 

[mgookin]

If you already have a lighting protection company involved I'll stay out of it other than to say you may want to contact a few companies to see what they suggest. (same as we would do in bidding out construction work)