Just bought a place and want some more opinions on what i have and if its correct. Metal frame dock, walkway and swim ladder are bonded #6, top of walkway at shore bonded to ground rod with #6. Stiff arm on other end of dock is not bonded. I believe it should be. Outdoor panel at top of walkway at shore is a main lug panel fed from the house, 4 wire system on standard two pole breaker. 4 gfci breakers in outdoor panel feeding individual branch circuits on the dock. All device boxes on the dock are bonded and made up to the ground bar in the outdoor panel, however the ground source for the outdoor panel is the ground coming from the house. It is not bonded to the ground rod. Neutral and ground are not bonded in the outdoor panel, I don't believe they should be, however I feel like the ground bar should also have a #6 going to the rod. Confused about the rule stating the feeder has to have its own egc. Also should there be a main breaker in the outdoor panel? Code states there must be a disconnecting means at the shoreline/top of walkway, do the breakers count as a disconnecting means or are they trying to specify ONE disconnect to de energize everything??
Residential dock grounding
- Thread starter JB85
- Start date
A photo would help. A dock panel (like on the dock at a marina) are typically protected by a Ground Fault Protection of Equipment (GFPE) feeder breaker and don't require a ground rod. A panel at a residence up away from the dock on say a equipment shack would have a ground rod and not need a GFPE breaker though I have seen them with GFPE breakers. See NEC articles 555 and 682 especially 682 part II and 555.53.
correct see explanation below
yes may not need to be a #6 but yes
It says your a substation electrician which I take to mean you work on the utility side which is a 'Multi Grounded Neutral' or (TN-C) system where neutral and protective conductor functions are combined into one bare wire.
In a NEC system after the service disconnect a MGN (TN-C) system is no longer used. The standard is to separate the neutral from the 'equipment grounding' or protective conductor creating a TN-C-S system, so a feeder would treat a neutral as if its 'live' and its only job now is carry neutral current, and the 'equipment ground' AKA protective conductor is used to bond all metal parts, ground rods etc.
Last edited:
Eddie702
Licensed Electrician
- Location
- Western Massachusetts
- Occupation
- Electrician
I would assume with 4 breakers in the panel you shouldn't need a main breaker as you can kill the power with 4 hand movements. Usually 6 is allowed.
Fred B
Senior Member
- Location
- Upstate, NY
- Occupation
- Electrician
What you have is covered under 555.13
555.13 Bonding of Non-Current-Carrying Metal Parts.
All metal parts in contact with the water, all metal piping, and all non-current-carrying metal parts that are likely to become energized and that are not connected to a branch circuit or feeder equipment grounding conductor, shall be connected to the grounding bus in the panelboard using solid copper conductors; insulated, covered, or bare; not smaller than 8 AWG. Connections to bonded parts shall be made in accordance with 250.8.
682.32 Bonding of Non–Current-Carrying Metal Parts.
All metal parts in contact with the water, all metal piping, tanks, and all non–current-carrying metal parts that are likely to become energized shall be bonded to the grounding terminal in the distribution equipment.
Also you mention a swim ladder so might want to contemplate the point made in 555.10 sign requirement and the Mike Holt references below.
555.10 Signage.
Permanent safety signs shall be installed to give notice of electrical shock hazard risks to persons using or swimming near a docking facility, boatyard, or marina and shall comply with all of the following:
(1) The signage shall comply with 110.21(B)(1) and be of sufficient durability to withstand the environment.
(2) The signs shall be clearly visible from all approaches to a marina, docking facility, or boatyard facility.
(3) The signs shall state “WARNING — POTENTIAL SHOCK HAZARD — ELECTRICAL CURRENTS MAY BE PRESENT IN THE WATER.”
If you are providing power out to the dock there is a potential for ESD Mike Holt video:
555.13 Bonding of Non-Current-Carrying Metal Parts.
All metal parts in contact with the water, all metal piping, and all non-current-carrying metal parts that are likely to become energized and that are not connected to a branch circuit or feeder equipment grounding conductor, shall be connected to the grounding bus in the panelboard using solid copper conductors; insulated, covered, or bare; not smaller than 8 AWG. Connections to bonded parts shall be made in accordance with 250.8.
682.32 Bonding of Non–Current-Carrying Metal Parts.
All metal parts in contact with the water, all metal piping, tanks, and all non–current-carrying metal parts that are likely to become energized shall be bonded to the grounding terminal in the distribution equipment.
Also you mention a swim ladder so might want to contemplate the point made in 555.10 sign requirement and the Mike Holt references below.
555.10 Signage.
Permanent safety signs shall be installed to give notice of electrical shock hazard risks to persons using or swimming near a docking facility, boatyard, or marina and shall comply with all of the following:
(1) The signage shall comply with 110.21(B)(1) and be of sufficient durability to withstand the environment.
(2) The signs shall be clearly visible from all approaches to a marina, docking facility, or boatyard facility.
(3) The signs shall state “WARNING — POTENTIAL SHOCK HAZARD — ELECTRICAL CURRENTS MAY BE PRESENT IN THE WATER.”
If you are providing power out to the dock there is a potential for ESD Mike Holt video:
Yes we do gave a grounded neutral on most everything. I see with it being a 4 wire system from the house panel to the outdoor panel, and not having the NG bond outside, the neutral is current carrying all the way back to the panel in the house. All the way to the meter base actually, the service from the meter to the house is 4 wire with the NG bonded in the meter base. My confusion was seeing code requiring the ground with the feeder, and I have a ground established with the ground rod at the top of the walkway, yet they're not tied together. I wasn't sure if that was something that was incorrect or if it was supposed to be that way. At the moment the only thing the ground rod is doing is basically making the dock structure and walkway at ground potential. Almost like they have two separate ground systems, like one serving as GEC and one as EGC. In my world we bond at all ground points to keep and even potential across the yard
Ok so I simply need to run from the ground bar in the outdoor panel to the ground rod. We use #4 on our meter bases so I'll grab some of that. I have the signs. Thanks
I thought 6 was the magic number but its been about 15 years since I did commercial work. I couldn't find anything real cut and dry in the codebook about it. Thanks
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
This is nothing like a substation though. Workers in substation are wearing insulated sole footwear and a voltage from a surface of 10-20 volts to earth may not even be felt if you touch it.
Immersed in water is one of worst case electrocution hazards, drive all the ground rods you want, the water is generally going to be earth potential. If your grounded service conductor (neutral) has voltage drop of 2 volts on it, that means it and all the equipment grounding conductors that land on it have a rise in voltage of 2 volts above earth voltage. If you have a MGN for the medium volt distribution some the voltage could be coming from voltage drop on that system, all the grounded conductors are bonded together and grounded conductor basically the same potential across all the systems involved. You will feel that 2 volts to earth if you are in the water. might not even need to touch the dock, there very well might be voltage gradients in the water surrounding any conductive portions of the dock that are in contact with the water.
GFCI and GFPE does not protect against such a rise in voltage on the EGC and electrocutions still happen at docks even if everything was done in accordance with NEC. Best advice is keep people out of the water in dock areas with electric power on them and keep electrical items as minimal as possible on them as well. Unfortunately if it is a metallic dock, it will end up being bonded to the EGC of the feed coming to it. This puts it at neutral to earth voltage of the service even if the feeder circuit is opened.
I don't have the neutral and ground bonded at the dock or house though. The only point on the property that is NG bonded is at the meter base. I understand voltage gradients, we call it step potential...same idea. I agree with water being at earth potential, thats why the dock frame, ladder, walkway etc is all bonded together and also at earth potential via ground rod at top of walkway. What i wasn't clear on was the lack of the grounding bar in the panel at the top of the walkway being tied to the ground rod also.
Last edited:
Fred B
Senior Member
- Location
- Upstate, NY
- Occupation
- Electrician
Code only says "555.13.....not smaller than 8 AWG. Connections to bonded parts shall be made in accordance with 250.8"
As opposed to a 680 installation Equipotential Bonding, 555 installations shall have all metal on dock either connected all the way back to branch or feeder source panel by means of the EGC of the branch or feeder or a separate "not smaller than # 8 conductor" back to the panel EG bus. Most 120V outlets and lighting will (or should have) have an EGC that should be connected to any metal enclosure. If these do not have an electrically continuous connection to the dock a separate connection of the "not less that #8" would need to be added for all the metal dock components such as the "swim ladder" and dock surface.
How far is the panel from the dock? May need EPB and equipotential plane as indicated in 555.14. As to the 4 breakers and disconnect do all 4 of them actually feed onto the dock? If so would recommend a main disconnect as found in 555.36
As to the 4 breaker in the main lug panel and disconnect being at the house panel it may be an issue related to 555.36(C) a review of that section will help you to see if there is an issue with not having an emergency disconnect, within sight, that disconnects all the power potentially supplied to the dock. this might be a "good idea" even if the criteria in 555.36 are not applicable for your specific installation, particularly with the "swim ladder" originally mentioned. And Even if not, I have been seeing many more "electric" boats and jet ski showing up on the lakes in our area and they want charging at the docks, then you do meet the requirements of 555.36 even if "shore power" is only 120V to a charger. Look at the enhanced content of 555.36 for the rationale for this requirement (Electric Shock Drowning). (review the referenced Mike Holt video from post #4)
Where is this ground rod here mentioned? "Stiff arm" if metal should be bonded unless it is physically and electrically connected to the rest of the dock. A simple meter test would be able to confirm this.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Voltage drop still occurs on the current carrying grounded conductors in the service neutral and POCO's MGN in the distribution system. The ECG you run out to the dock is still bonded to the service neutral and this voltage is imposed on it and everything it is connected to. You can drive all the rods you want at the service or even the dock it will only equalize the voltage in a small area surrounding that rod and will be zones if differing volts as you move away from the rod.
art 680 for swimming pools takes care of this with equipotential bonding of points that may contribute to touch potential to keep everything in the pool at the same potential, even if there is still an overall voltage to true ground. Is impractical to do so with natural bodies of water or even larger man made bodies of water leaving you with potential voltage gradients in those applications that you wouldn't have in properly done swimming pools.
IMO NEC has failed us with how to handle this, and we keep hearing about electrocutions in these applications even where the install is NEC compliant. You can install isolation transformers, but bonding rules still would bring any voltage rise that is present on the grounded service conductor to the dock. Allowing swimming near any dock with electric power is not a great idea. But you also don't need someone to fall into the water accidentally and then get electrocuted trying to get back onto the dock. They need to require the supply to the dock to somehow have total isolation from the grid to lessen these incidents.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
EP sort of makes no sense being required only at electrical equipment when the entire dock if a metal structure is effectively part of the EGC, and is impractical to install in the water surrounding the dock. We need to find a way to isolate the systems supplying these docks from the utility system. I myself would feel much safer in the water around a dock that had a supply run to it that was isolated from the main premises wiring and had it's own grounding system or even had an ungrounded supply with ground monitoring system that would do more than just turn on an indicator that likely gets ignored if a ground fault is detected
Yeah there is nothing we as electricians can do to prevent that, thats why attorneys call it electrical trespass.
A GFPE breaker on a feeder to panel that supplies any swimming area or dock I think is the best protection you can offer, most electricians will consider it overkill.
They sell all these green light gizmos now for 'safe swimming' but really if you want enhanced protection I think the money is better spent on a GFPE feeder main.
With NEC complaint equipment grounding in place a line to ground fault will pull more than 30ma within a few cycles.
GFCI's are somewhat fragile devices, especially the receptacle type, and subject to the environmental harshness of waterfront electrical system, wind driven rain, ice, insect nests, salt water ...
GFCIs can fail and they can fail without switching off the power, a GFPE feeder breaker will trip as a fallback.
I actually was working on outside light the other day with its breaker off and forgot the panel was fed from a 30ma GFPE breaker like you'd have to a dock panel, when I cut the cable with my dikes the GFPE main instantly tripped in the service.
To @JB85 the substation electrician will likely be familiar with the concept as its like the newer style protective relaying utilities do like 'advanced' recloser protection for sensitive earth fault (SEF) protection.
Last edited:
I agree with that, not sure about a 100% fail proof way though. And you know people aren't going to stay out of the water. The dock alert systems are going to become more required in the near future
Stiff arm is at the other end of dock going to land. Its a metal hinge point but im not going to rely on that, ill bond it to the dock frame next time im there. Yes all 120v has egc and is bonded at every device/box and is made up at the equipment ground bar. I may add a main breaker anyways, just as a further means of an emergency disconnect. Can't hurt anything
Agreed. I'll look into changing the feeder breaker as well then.
Also as far as the receptacles, other stuff I've done in prefer to use standard recess on a ground fault breaker. The gfce receps don't last
- Location
- Illinois
- Occupation
- retired electrician
Second building or other structures supplied by a feeder have required both an EGC run with the feeder and a grounding electrode conductor connecting the EGC to a grounding electrode at the second building or structure. They are not separate grounding systems as the feeder EGC is connected to the main building grounding electrode system via the main bonding jumper.
Also the connection to earth does not keep points at ground potential. Typically there is a voltage on the neutral as a result of various voltage drops, and all that happens when you connect that to a grounding electrode is that the voltage of the earth is raised, in a small area around the grounding electrode, to match the voltage on the neutral.
I'm going to get that made up next time im there. I figured it should be but just wanted to check and make sure it wasn't something weird with it being a dock. I'm guessing it was just incorrect with the previous owner
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
GFCI and GFPE both will not detect voltage rise in the EGC. They only trip if the protected conductors (L1, L2, L3, N) have leakage to something not connected to the protection device(EGC or anything with continuity to it or true ground, other circuits is possible but probably not so common especially in this application) that exceeds the trip threshold. Neutral to earth voltage incoming via the grounded service conductor through the main bonding jumper then out to the dock via the EGC of just 2-5 volts can be deadly to someone in the water that touches any part of the dock that is at that potential. If said voltage is much higher they may not even need to touch it, just need to be too close while in the water and end up across a voltage gradient in the water and might become incapacitated and can not move out of said gradient. GFCI/GFPE won't detect this, and won't disconnect it even if you manually turn off the feeder breaker, you need to open the EGC to make this go away, hence the problem with current NEC requirements not addressing this issue, or at least not addressing them sufficiently. Warning signs isn't enough, people ignore them for various reasons, even those that may understand the hazard pretty well may still ignore them in some cases. Thing is you often don't know there is any problem in these applications until there has been an injury or death.