transformer on a floating pier

[jnava]

Will the NEC allow me to mount a 150kVA (480V to 208Y/120V, 3-phase) transformer on a floating pier? I understand that Article 555.5 says I need the bottom of the transformer to be above the elec. datum plane. And if it is allowed, getting back into the building is not feasible for the GEC (grounding electrode conductor), what can I ground it to? Any thoughts?

 

[charlie b]

Yes the NEC would allow a 480-120/208V transformer on a floating pier. See 555.4 (voltage on pier not to exceed 600 phase to phase). However, there is another code that also deals with this question. I dealt with it about 5 years ago, and no longer remember where it is to be found. There were disagreements in the interpretation of that code, with regard to whether it was considered safe to bring 480V to a pier. I only remember contending that it was safe, and therefore within the rules of that ?other code,? and that I won the argument with the port authority.

Why do you say that the GEC cannot be brought back to landside?

 

[jnava]

I don't think there's going to be a problem with the voltage as there is an existing 480V feeder serving a boat out there already. I plan on using that 400A feeder currently fused down to 100A. I plan on putting new 400A fuses in the building so the feeder is fully rated for 400A. I plan on providing a new 400A panel w/ a 100A c/b to refeed the boat and another c/b to feed the xfmr. The problem is I can't get back into the building w/ the GEC. I can get back to landside, but don't know what to ground it to.

 

[augie47]

ground

ground

enter one electrical inspector with scuba gear
(sorry, couldn't help myself---your question is legimate-but I just pictured a ground rod under 12' of water and a very zealous inspector)

 

[charlie b]

If this were a separate building on land, with the first building feeding power to a second building, and if you installed a transformer in the second building, there would not be a need to run the GEC back to the first building. You have a separately derived system that requires its own grounding electrode system. You would put a ground rod (or two) at the second building, or use whatever electrodes are available.

I do not know a Grounding Electrode System is designed in the case of a floating pier. Yes, I do believe a ground rod or two pounded into the bottom of the lake would constitute a valid grounding electrode. But I doubt it is often done that way. If you can bring GEC to landside, and put a rod (or two) into the ground near the head of the pier, that should suffice.

But I have never gotten that deep (pun intended and not regretted :roll: ) into the design of a marina. I do not know how this is normally handled. Someone else will have to finish this story.