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Niko #198421 01/21/11 02:15 PM
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Quote
How about a dwelling unit that is built on a permanently constructed deck that is on the body of water?


How do you construct a deck permanently?

Is it on pilings? If it is wooden pilings, I don't know the "proper" way to ground. If they are steel reinforced concrete pilings, wouldn't it be the same as a foundation?


LarryC #198427 01/21/11 04:47 PM
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Sparky summed it up. Floating buildings are covered in 553.

Quote
553.8(D) Grounding Electrode Conductor Connection. The grounding terminal in the service equipment shall be grounded by connection through an insulated grounding electrode conductor to a grounding electrode on shore.
Handbook commentary
Grounding of electrical and nonelectrical parts must be connected to a grounding bus at the building panelboard. An equipment grounding conductor must be included in the feeder supplying the building and connected to the grounding terminal at the service equipment. For conductor sizes 6 AWG and smaller, the equipment grounding conductor must be provided with green insulation or green insulation with a yellow tracer. An insulated grounding electrode conductor must be installed between the service equipment and the grounding electrode on shore.


Greg Fretwell
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It is interesting that I don't see anything particular about the grounding for a building built on a pier beyond Article 555 and that does not talk much about service equipment. Personally I would want to the the service disconnect up on the shore and a feeder with the EGC meeting the requirements of 555.15 (basically an insulated wire).
I see nothing that relieves the installer from following 250 part III when it comes to the electrode and nowhere in there does it allow a connection to the water to be a ground electrode.

In a "boat" with no shore connection, a bronze grounding plate in the hull is common.


Greg Fretwell
Niko #198429 01/21/11 05:19 PM
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As usual, we have at least two separate issues. Let's identify them, and maybe the question will answer itself.

The first is the iisu of clearing faults. This requires a low-impedance path back to the PoCo transformer, and the "ground rod" has no role. Often the neutral is this path.

Then there is the variation: a fault from a 'hot' wire to a metal case. That's where we need a good path between the fault and the PoCo neutral, and this is what we use the green wire for. IMO, "stray current" issues arise most often because this path is inadequate.

The "other" grounding has to do with lightning and static electricity. Those are the only forms of electricity that want to return to planet earth. Perhaps at some point boats with non-conductive hulls will be required to 'bond to water' much as we now require pools.

If a boat is not receiving power from shore, there is no reason for there to be any electrical bond with shore. In that instance, there needs to be a low impedance path back to wherever the electricity was created.

Now we enter the paradox of having multiple power sources. That is, should there be a failure of the PoCo neutral, then we have just energized the entire marina. Since fresh water isn't such a great conductor, we WILL have voltage gradients severe enough to kill. Your ONLY protection in this instance comes from GFI's.

Niko #198432 01/21/11 08:30 PM
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Originally Posted by Niko
Is body of water considered ground?

The floating dwelling units have to ground their system. How about a dwelling unit that is built on a permanently constructed deck that is on the body of water?

How is grounding achieved? confused


The way I see it, you have to answer two questions to answer.

1) Is it floating?

2) Is it permantly connected to shore power?


If the "permanently constructed deck" is floating, AND not permanently connected to shore power, it is a boat.

If the "permanently constructed deck" is floating, AND permanently connected to shore power, it is a structure that must follow the NEC.

If the "permanently constructed deck" is NOT floating, AND not permanently connected to shore power, it is a stand alone system.

If the "permanently constructed deck" is NOT floating, AND permanently connected to shore power, it is a structure that must follow the NEC.


Last edited by LarryC; 01/21/11 08:31 PM.
LarryC #198436 01/21/11 09:59 PM
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Niko Offline OP
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i am not working on a floating building or a deck.
We have some floating buildings about an hour north of where i am so a thought popped in my head as to how their grounding electrode system is done.

I never knew that there is a section in the NEC that applies to that.



Thank you all for your replies.


Be kind to your neighbor, he knows where you live

Niko #198443 01/22/11 03:09 AM
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To answer the OP and to prevent confusion about grounding, the ocean is not an acceptable grounding point as far as the NEC is concern. On float houses, houses on piles, boat houses, any structure which are "permanently" attached to the shore falls under the local electrical code.

In regards to the OP and clarify some of the following posts, the grounding electrode system (i.e. Rods, pipes, plates, rings, etc.) have nothing to a structure's internal wiring or our trade calls, equipment grounding conductors. They both do totally separate things. The simplest way of putting it is the grounding electrode system protects a structure from external sources like near by lightening strikes and faults in the distribution system like a faulty transformer or downed primary on a secondary line. The equipment grounding protects the same structure from internal faults like ground faults. With that said, let the public lashing commence but in a new post


"Live Awesome!" - Kevin Carosa
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Niko Offline OP
Member
I think most of us know the difference between EGC and GEC.

But why isn't the water an acceptable grounding point that may serve in place of the earth.

on a second note, I think the water would be a great conductor specially salty water. Am i wrong?

i guess my basic question is Can body of water be considered earth?



Last edited by Niko; 01/22/11 03:58 AM. Reason: add

Be kind to your neighbor, he knows where you live

Niko #198445 01/22/11 04:32 AM
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Salt water is an excellent conductor but NFPA has never recognized it in part III of 250 so we are left with terrestrial ground electrodes.


Greg Fretwell
Scott35 #198449 01/22/11 12:52 PM
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Clarification time.
My comment on pg 1 was to Larry; "YES" the NEC does apply; it was not a 'yes' to water being acceptable as a 'ground'.

That said, I apologize for the above; workplace confusion and to much multi-tasking!



John
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