AC ground wire connected to DC ground engine negative terminal. yes or no

Discussion in 'OnBoard Electronics & Controls' started by sdowney717, Oct 1, 2024.

  1. sdowney717
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    sdowney717 Senior Member

    upload_2024-10-1_16-58-47.png
    Noted sailing expert and electrical engineer Stan Honey discusses how to have perfect ground systems for AC, DC, RF, lightning, and corrosion protection.
    Marine Grounding Systems | West Marine

    I do believe my AC ground wire and DC negative are joined somewhere
    My metal monel fuel tanks are also joined to the ground somewhere.

    Underwater metal, I ungrounded many years ago. But of course SS prop shaft bolted to engine and has a bronze prop and they are electrically connected by nature
     
  2. sdowney717
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    sdowney717 Senior Member

    one thing to note, if you reverse polarity 120 VAC power plug incoming shore power, if you have GFCI breakers, they will trip off the power.
    They detect reversed AC polarity which is a good thing.
    Since my 8 breaker positions old Square D QO distribution box is full of AFCI-GFCI combo breakers, I have pretty good AC protection for the boat.
     
  3. Ike
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    Ike Senior Member

  4. rangebowdrie
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    rangebowdrie Senior Member

    The idea of connecting the AC green/grounds and the DC grounds together, (usually at the DC grounds/AC grounds busbars, not at the engine,) was simply to provide a low resistance pathway to ground to prevent someone in the boat from being electrocuted, (leaning against a water heater that's leaking currant and touching a seacock for example).
    However, this whole concept is predicated on having the engine electrically connected to the water via the prop shaft.
    All of that was long before GFCI devices were in use, and when ESD was not commonly known.
    Now we have the knowledge and the devices to keep people both aboard or in the water from electrocution and any AC from ever getting to the water.
    And we can also stop using the engine as a "Grand Central station" for stray electrons, and for sure stop using the engine as a pathway to ground for a lightning strike.
     
  5. Ike
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    Ike Senior Member

    As you can see this is a controversial subject. It has been argued ad infinitum in ABYC meetings, at ISO meetings, and when I was working for the USCG we used to discuss this frequently. However, if I were in your situation and concerned about it I would thoroughly research it, and consult with either an Electrical Engineer who specializes in marine electrical systems, or a certified marine electrician. I have always advised people to follow the ABYC standard E11 AC and DC Electrical Systems For Boats. If you want to vary from that then make sure it meets the same level of safety. Even the USCG allows variations from the electrical regulations (which do not include AC systems for recreational boats) if they meet the same level of safety. I would agree that the USCG regulations were written in the 70's an 80's and are seriously in need of updating. However, ABYC, and ISO standards are constantly updated at five year intervals. They are the most up to date standards and what I based my web page on.
     
  6. rangebowdrie
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    rangebowdrie Senior Member

    The guy who "wrote the book" for the electrical and corrosion control classes for someone to become an ABYC certified electrician, as well as the main impetus behind the requirements for marinas to furnish GFI protection on the docks and has taught classes at the CGA and is a recognized expert witness for electrical/corrosion control cases in court has been a good personal friend of mine for ~25 years.
    I happened to be at the marina where/when he lost a son to ESD.
    We have had endless hours of discussion on electrical/corrosion matters over the intervening years.
    I will say this; The ABYC "standards" do little to nothing to prevent stray current from eating away at the metals in a boat and in the main are hide-bound and out of date in much of their application.
    Their standards are quite good at providing electrical paths TO the water, but very deficient of keeping electrons OUT of the water.
     
  7. sdowney717
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    sdowney717 Senior Member

    GFCI-AFCI breakers have become much smarter, they have firmware now. They detect mis wired and other strange potentially dangerous electrical conditions for people and structures.
    Primarily you do not want to kill people by electrocution on a boat or swimming in the water, secondarily you do not want stray currents corroding underwater metals or burning your boat in an electrical fire which can spread to other people's boats and also harm and kill people.

    You can get decent protection using GFCI-AFCI breakers a long-time standard which on land their use keeps being expanded by the NEC.

    ELCI allows a much higher stray current before shutting down the power. I cannot do much about other people's boats.
    ELCI is a compromise that will not keep you from being killed, it is for 'equipment protection', not people protection.

    I have been able to create such a tight AC system, a GFCI power cord on incoming shore power can power my entire AC system on the boat without tripping off, and I think it is a worthy goal to pursue.

    For example, I am hauled out now. I sometimes need power inside the boat. I can take the GFCI protected marina extension cord and plug in the shore cord on the boat and everything works without the GFCI tripping off the power. If I reverse the polarized plug, (my ground wire on cord broke off, need to fix), that marina shore GFCI cuts off the power. I decided to try it, and sure enough, I had to walk over and reset the GFCI on the shore power. Marina has a whole bunch of GFCI outlets people plug into for working on the hard. I wonder if their slips power has GFCI breakers, I haul out there I don't slip there. I should walk over and look. Seems really dumb to have GFCI for shore power and no GFCI for slip power.

    Even my very old CruiseAir Heat Pump, and its water pump, I have on AFCI-GFCI breaker, and it works great. Long time ago it was not, and the water pump had an issue with a wire, and I reached down to feel outflow temp, and I got shocked. Found the wire box had gotten wet from rain and cause a stray current to go into the water.

    I got shocked and was shocked at how easy it was to get shocked, everything was running fine, but I got shocked.
     
    Last edited: Oct 3, 2024
  8. sdowney717
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    sdowney717 Senior Member

    And likely even though my AC system is one of the safest for a boat anyone can have, I am sure is not meeting their ABYC boat standards as my system is NEC based and uses QO Square-D boxes and breakers, which came on the boat originally back in 1970. I was able to upgrade it as it is still one of the best products for electrical panels around. I don't really care about meeting all the ABYC electric codes as I think the boats standards are not as good as the NEC for land. As long as it is really safe, that is all that matters to me.
     
  9. sdowney717
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    sdowney717 Senior Member

    And the GFCI also self test continuously, so when they fail, they will trip off the power, that has been around 10 years now.

    https://hubbellcdn.com/literature/Wiring_WLBG001.pdf
    AUTOGUARD® Self Test Technology 1st introduced by Hubbell over 10 years ago! …self test monitoring now required in 2015 UL 943 GFCI Safety Standard… Hubbell AUTOGUARD® GFCI receptacles continually test and monitor for “people protection capability” automatically. This patented safety feature includes disconnecting power to the receptacle if critical components are damaged and GFCI protection is lost. GFCI auto-monitoring is conducted continuously within every 30 seconds. Also, clear visual indicators are provided on the device face representing power status, trip condition, ground fault condition and end of life status. In addition, for added safety, power will be denied to the receptacle face if reverse wiring of line and load was to occur

    so there is no reason or excuse not to have GFCI today, on your boat and at marinas, around your home.
    Technology keeps on improving. In the years since I put in Square-D QO AFCI-GFCI combo breakers, none have failed. I did have an older GFCI breaker that did fail, and Square-d gave me a new one. The reason was a voltage surge from a gen maybe or maybe came in from utility power. I do think the new one has improved protection from that one which was maybe 20 years old.
     
  10. sdowney717
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    sdowney717 Senior Member

    Right now, there are 2 circuits I don't have GFCI on, one is the Victron battery charger, other is the fridge. I suppose fridge I do have concerns about about a nuisance trip and same with battery charger. I have run both on the GFCI and they did not trip off. I look at those 2 circuits as important and I don't think dedicated circuits to either is going to be a problem. I think if you have GFCI on the dock it could be a problem which is a knock against it, which is one reason for using ELCI as a compromise. Nothing is perfect, everything is sort of a compromise. If I had GFCI on the marina pedestal, I would not complain. I know some people have fancy setups that will send a text message if power goes out like at a boat. I don't have that, not that rich.

    Here I am just talking off the top of my head...
     
  11. rangebowdrie
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    rangebowdrie Senior Member

    Me too.
    Everything, and I mean everything in the boat that uses AC is on a GFCI.
    All the permanently mounted gear, like the battery chargers, refrigeration, water heater, etc., are all hard wired thru GFCI devices, and all outlets are GFCI protected, and the shore power cord plugs into a GFCI outlet on the dock.
    Another GFCI device is on the boat between shore power inlet and the panel.
    For a person to be shocked would require the three GFCI devices in that circuit path to all fail in the on position.
    There is no connection between the AC green/grounds and the DC grounds.
    One of the big secrets to having zero electrical problems, (AC or DC,) on a boat is DRY wiring.
    When you are sitting down in my boat there is no AC wiring below shoulder level and the only DC wiring that is below waist level is for the bilge pump, freshwater pump, and the main battery cables that feed the panel/engine.
    Rat's nests of wiring strung helter-skelter underneath floorboard levels/in bilge areas is just asking for trouble, keep the wiring high and dry.
     
    Last edited: Oct 3, 2024
    sdowney717 likes this.

  12. sdowney717
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    sdowney717 Senior Member

    That is great. All my AC wiring is out of the bilge, cant get wet unless it sinks or humidity condensation which can get things really wet. I suppose the gen location is a bilge area, but I keep the AC wires up there too.
     
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