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Joined: Oct 2004
Posts: 18
Hello, I am new here and I'm an electrician in California. On this job, we are mounting transformers (480V delta to 208V wye) out on a floating dock system. There is an appropriately sized equipment ground conductor coming in with the 480V conductors feeding the line side. The floating dock system is all constructed of 2" X 2" X 1/8" wall aluminum square tubing with plastic floats bolted to the bottom and deck boards screwed to the top. My question is, what is the best way to install the grounding electrode conductor? My idea was to attach it directly to "building steel" as I would in a building, then have a monster ground conductor bonding the whole dock system to the ground rod on shore (where the 480V comes from). The city is suggesting we run another ground wire parrallel to the equipment grounding conductor, or just upsize the equipment grounding conductor and use it for both the equipment ground and the grounding electrode conductor. What do you think? Thanks brothers and sisters, Ben

2017 / 2014 NEC & Related Books and Study Guides
Joined: Oct 2004
Posts: 18
What? Nothin? I know I put this post in the wrong section, but still thought I might get some help! [Linked Image]

Joined: Jul 2002
Posts: 8,407
Likes: 2
Welcome along Ben,
I've moved this to a more appropriate area.

[Linked Image]

Joined: Dec 2000
Posts: 38
Does the transformer have to be on the dock?
It can't be shore mounted I would do as they say in article 553.8 (D) run an insulated grounding electrode conductor to a grounding electrode on shore.

Joined: Mar 2005
Posts: 1,803
Is the ocean (salt-water) 'ground'?


Wood work but can't!
Joined: Nov 2000
Posts: 2,148
I would install a primary EGC, sized per 250.66 for the transformer secondary conductors and bond to the dock structure.

Joined: May 2003
Posts: 2,876
e57 Offline
This is an odd question maybe? But how are you getting out on the dock? Its a floating dock, so I imagine it being flexible and in constant movement. If it is in multiple sections you may have to bond the dock, and all other items like water and such on each section.

Art 553, and 555 are a good read, especially 555.15. You're still in '99 for the time being, Cali wont go to '02 until October, then wait for all the cities to change up to it too. But interesting how this install could change in '02.

(1999 and 2002 read slightly different. And the '02 says all transformers must be approved for the location, and lots of talk of the "Electrical Datum Plane".)
555.2 Definitions.
Electrical Datum Plane. The electrical datum plane is defined as follows:
Throughout Article 555, the physical location of electrical equipment is referenced to the electrical datum plane. This term is used as a horizontal benchmark on land and on floating piers. The definition of electrical datum plane encompasses areas subject to tidal movement and areas in which the water level is impacted only by conditions such as climate (rain or snow fall) or by human intervention (the opening or closing of dams and floodgates). In either case, the term covers the normal highest water level, such as astronomical high tides. The term does not cover extremes due to natural or manmade disasters.
(1) In land areas subject to tidal fluctuation, the electrical datum plane is a horizontal plane 606 mm (2 ft) above the highest tide level for the area occurring under normal circumstances, that is, highest high tide.
(2) In land areas not subject to tidal fluctuation, the electrical datum plane is a horizontal plane 606 mm (2 ft) above the highest water level for the area occurring under normal circumstances.
(3) The electrical datum plane for floating piers and landing stages that are (a) installed to permit rise and fall response to water level, without lateral movement, and (b) that are so equipped that they can rise to the datum plane established for (1) or (2), is a horizontal plane 762 mm (30 in.) above the water level at the floating pier or landing stage and a minimum of 305 mm (12 in.) above the level of the deck.
Marine Power Outlet. An enclosed assembly that can include receptacles, circuit breakers, fused switches, fuses, watt-hour meter(s), and monitoring means approved for marine use.
555.4 Distribution System.
Yard and pier distribution systems shall not exceed 600 volts phase to phase.
555.5 Transformers.
Transformers and enclosures shall be specifically approved for the intended location. The bottom of enclosures for transformers shall not be located below the electrical datum plane.
555.7 Location of Service Equipment.
The service equipment for floating docks or marinas shall be located adjacent to, but not on or in, the floating structure.
The requirement covering service equipment location in 555.7 is similar to that in 553.4 for service equipment supplying floating buildings.
555.9 Electrical Connections.
All electrical connections shall be located at least 305 mm (12 in.) above the deck of a floating pier. All electrical connections shall be located at least 305 mm (12 in.) above the deck of a fixed pier but not below the electrical datum plane.

Mark Heller
"Well - I oughta....." -Jackie Gleason

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