JWelectric
Electrical Contractor/Instructor
IMO, to compare a utility to an automobile is totally like discussing apples and oranges because the automobile is like a completely self contained utility and all of it's users/customers. Another big difference is that the modern automobile contains RF circuits, AC circuits, and DC completely self contained.. if compared to a dock that's like installing a gasoline engine powered generator on a dock rather than running electrical wires from a service panel hundreds of feet away... no more need for an earth ground than installing a ground rod to an automobile.
In common vernacular just about everyone uses the term "ground" for "neutral". In my posts I have tried to avoid this confusion. If we get particular about the correct use of the language then we should refer to it as a "neutral connection or neutral side of the circuit".. a short cut is to simply say "neutral (for continuous connection to the neutral of the transformer)" or "ground (for continuous connection to earth)". As a professional multi-skilled laborer I have to know the difference.
Back to dock wiring.. Wouldn't it or would it not be... safest to simply NOT directly connect any earth ground at all to a metal dock? All earth ground wires terminate at receptacles. All wires in insulated (PVC) and all outlet & switch boxes be made of a non-conductive material? All switch box panels on the dock insulated from contact with the dock? .. .this would be comparable to how any appliance is wired, everything insulated from human contact and totally avoids any possibility of even a tickle voltage from the difference in stray voltages, voltage drops and any kind of electrical currents. It appears that this would certainly satisfy the NEC requirement that the green wire/ground be a continuous connection all the way back to the service entrance. No need for epg's, grids in the earth, buried hamster cages, ground rods... nothing except circuit wires to provide electricity and protection from faults. KISS... Keep it simple suckah. For one thing... wiring a dock is the big time equivalent of running an extension cord to the dock. You would not connect the ground wire of an extension cord to a dock or metal building....
As to the generator at the dock it would depend on the type of generator being used as to whether or not a grounding electrode system would be required. A self contained portable generator would not require a grounding electrode but a permanently installed generator would require a grounding electrode system.
There is no way on earth to make stray voltages disappear. It would require that there be no more electrical storms and both the north and south poles would have to be neutralized to stop all stray voltages or gradients voltages through earth’s crust. The temperature would need to be constant over the entire earth with no cold fronts colliding with warm fronts.
All theses combined causes the earth’s crust to have voltages without there ever being any type of electrical current produced by the utilities or any other man made current.
The thought of comparing the 12 volt DC system to a 120 volt AC system as being like comparing apples to oranges is untrue. The only two things that change are the type of voltages and the numbers. The equations are the same.
As to calling the neutral the ground conductor is not exactly correct either. The neutral conductors that supply our homes are a current carrying conductor just as the ungrounded (hot) conductors. In a 120 volt circuit the neutral carries just as much current as the hot conductor. The equipment grounding conductor never carries current unless something bad goes wrong.
The reason the neutral is called the groundED conductor is because the utility connects this conductor to earth. In most cases for a dwelling unit the return or neutral of the high voltage supplying the transformer is connected to the neutral of the secondary (the one coming to our homes) and to the grounding electrode conductor at the utility pole or pad mounted transformer. It is called groundED by the NEC because by the time the electrician gets to wire the building this earth connection is already established or past tense.
The electrician installs the equipment groundING conductor at the time of the installation therefore in the present tense. This grounding conductor is then bonded to the grounded conductor and the grounding electrode conductor at the service. The grounded neutral is earth grounded twice, once by the utility and again by the electrician at the service equipment and can be earth grounded for the third and more times each time the conductors leave the service equipment and go to another building or structure on the outside.
The purpose of bonding this metal dock to the grounding electrode for the panel supplying the metal dock is in case one of the circuits supplying equipment such as lights, receptacles, boat lifts, and the such on the metal dock should come into contact with the metal dock there would be a low impedance path back to the source supplying power to that dock in order to open the overcurrent device thus stopping the flow of current.
This bonding is not to relieve the voltage gradients between the water and the metal or wooden dock. A ground rod will not relieve this current. An equipotential grid does not relieve these stray voltages but instead brings everything to the same or equal potential therefore no current flow.
Even if everything was installed in non-metallic enclosures and raceways it would not relieve the stray voltages. There would still be the step potential between the water and the dry ground.