Container Reefer Plugs and Grounding

[GoldDigger]

So each upper container rests only on the stack below it?
And the bottom one rests on asphalt or dry concrete?
That certainly could have enough resistance to ground to avoid tripping breaker, except for the fact that other containers in the same stack should have good EGCs.
Sounds like OSHA would like to see a portable tester for the cord each time a container is plugged in.

 

[suemarkp]

I believe 250.50 serves my purpose. Were none are present, one or more shall be used. Plus I think we can go beyond the code to make things safer. Please read all post.

I still don't see how 250.50 is going to help you. It could be debatable as to whether a ground electrode system is required at these structures (are they within a building, or outside detached from anything else). Even if you install a ground electrode, its resistance is most likely going to be too high to trip a 30A breaker at 277V to ground. Why didn't the miswired refer car trip the breaker by touching the properly wired ones stacked under or above it -- is the outside skin insulated? If that didn't trip the breaker, a 10 ohm earth connection will be even worse.

If you install a conductor from each refer to a common ground rod, that will work. But it isn't the earth electrode that is helping, but the fact that all the refers are bonded together, which just happens to be at the ground electrode. Tying each refer to the "ground grid" or your 4 story racks would also work (e.g. extend it out to the area where the refers are set, assuming there is a way to ensure refer metal to grid contact).

I think the NEC assumes the cord being wired correctly for safety requirements. I don't see mitigation for improper cord wiring in most typical installs (e.g. an appliance or other equipment t that is free standing), and it is certainly a dangerous situation with 277V present. Sounds like a second method of bonding, or verifying the cord is correct before each use, would be prudent.

Did the 400A GFCI trip when the person got shocked?

 

[Smart $]

So each upper container rests only on the stack below it?
And the bottom one rests on asphalt or dry concrete?

Ditto on those questions.

That certainly could have enough resistance to ground to avoid tripping breaker, except for the fact that other containers in the same stack should have good EGCs.

As I mentioned earlier, the bad one may have been the first to be plugged in. Either that or there is isolation between units. Could be something as simple as paint... but then that would seem to imply the shocked worker touching two containers shouldn't have been shocked... unless some parts have non-conductive paint an other parts don't. ...???

Sounds like OSHA would like to see a portable tester for the cord each time a container is plugged in.

Agree. I think the Assured Equipment Grounding Conductor Program posted earlier is actually OSHA mandated... yet I think many believe it only applies to extension cords and portable tools.

 

[Smart $]

...

Did the 400A GFCI trip when the person got shocked?

All valid and noteworthy points on bonding vs. earth grounding.

I too wondered about that upon reading. In addition, I am curious whether the 480V system is grounded? If ungrounded, is there maybe confusion between GFCI and ground detector equipment? If grounded, is the GFCI equipment or personnel protection? Is there such a thing as a 400A GFCI breaker for personnel protection?

I also considered whether this installation falls under Article 626 for Electrified Truck Parking Spaces. GFCI for personnel is required for truck parking space equipment... but not for Transport Refrigerated Units (TRUs), which the reefer units under discussion would be classified.

 

[dudleydorightdad]

Shipboard hookup usually 3 wire non grounded service

Shipboard hookup usually 3 wire non grounded service

I have worked on a couple container vessels and usually there is a 480v 3 wire delta service for these vessels. And the shipping containers I have personally seen (not worked on, although hold journeyman refer rate from apprenticeship at naval shipyd) have been open drive units that run self contained when loading or unloading until after they are either lashed down after placement in the vessel at which point they are again hooked up to remote power. I know for a fact these vessels are equipped with ground detection equipment as stray ground current through the metal structure basically eats steel in salt water through electrolysis. So I would have to question was this container just repaired, just offloaded, miswired by the injured individual or? It sounds to me that there is missing information. These containers do not just sit on one another. There are 4 metal(bare) spuds that are inserted into the oval holes in each of the corners of a container before the next container is set upon it. When the spud is installed with the next container set in place it is rotated 90 degrees to lock it in place essentially creating one multi container assy. It would be physically impossible for these containers not to be bonded to one another through this process. Sound like something besides the facts stated are at play here. Just my opinion though. Oh and the laws of physics.

 

[charlie b]

I have worked on a couple container vessels and usually there is a 480v 3 wire delta service for these vessels.

I haven't gone through this thread in detail. But I think we are not talking about power to the vessel (which is an ungrounded delta). We are talking about power to the containers, and I think that is a 480V grounded WYE.