Engines must be grounded and joined with another negative wire

Discussion in 'OnBoard Electronics & Controls' started by sdowney717, Aug 4, 2021.

  1. sdowney717
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    sdowney717 Senior Member

    The additional negative grounding wire must be separate and equal to the negative wire used by the starter.
    Just found this today. I do have another large wire I can use, but the regs while they make logical sense, just keep getting more and more. My 1970 boat was not built this way. In the same theory regarding inverter grounding also applies to boat engines. Now, what I have noticed on my boat, if the negative starter wire is loose, the starter relay goes click, click, click as it does with a very low battery, the voltage drop simply cycles the starter relay and nothing happens like a burnt wire. Maybe my other ground wire connections allow enough current to flow they dont catch fire. Not in 50 years of this boat's life, has this ever been a problem, but of course there is no equal sized duplicate negative starter wire, joining both blocks together. Nor have I noticed this on other older boats. How about your boat?

    It seems to me, joining both blocks together with an additional wire of the same sized starter wire would meet the requirement. In my case, put the wire from head to head of the 2 engines. My generator is grounded and bounded with 2 additional large wires, so wont bother doing anything with that.
    My negative engine return wire is simply on the head, not on the starter, never seen negative wire directly on a starter. Would make it hard to fit, and they dont do that with cars either. And say if you took off your starter to work on it, then you have lost your engine ground which is not good.

    GROUNDING:

    CFR Sec. 183.415 33 CFR 183 Subpart I | Boat Electrical Systems | New Boatbuilders Home Page https://newboatbuilders.com/pages/33CFR_electrical.html On twin engine gasoline inboards there must be a ground connection for the starting (Cranking) motor and there must be a connection between the starting motors for each of the two engines. This should be the same gage wire as the wire from the battery to the starter. The reason for this is simple. If there is a fault, all the current flows through the ground wire. If there is no ground wire it will burn up the electrical system on the engine and may start a fire. ABYC requires this on all twin inboards, outboards and diesels.
    See Grounding and Bonding: Basic Electrical Practices Boat Building Standards | Basic Electricity | Alternating Current Practical https://newboatbuilders.com/pages/electricity12.html
    See also grounding of the boat's fuel system: Boat Building Regulations | Boat Fuel System https://newboatbuilders.com/pages/fuel.html
     
    Last edited: Aug 4, 2021
  2. gonzo
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    gonzo Senior Member

    The main problem is that if there is no ground wire connecting the engines and the current goes through another conductor, it can cause a fire. For example, the engine could be connecting through a low oil pressure alarm wire. This is an issue with separate batteries for the engines when the bypass (emergency start boost) switch jumps one engine to the other's battery.
     
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  3. sdowney717
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    sdowney717 Senior Member

    I know, it makes logical sense, my old boat was not built this way, but is relatively easy to add another ground wire. Just happened to find the website and thinking about it realized, I dont have an additional safety ground return wire equal in size to the main ground wire for the starter. 50 years later, I suppose now it gets the extra wire.
     
  4. Howlandwoodworks
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    Howlandwoodworks Member

  5. sdowney717
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    sdowney717 Senior Member

    It has a 6 gauge wire off the starboard engine block that runs into the AC distribution breaker panel connected to the ground bar buss. So, yes it is joined there.
     
  6. Ike
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    Ike Senior Member

    sdowney, thanks for the quote. Actually that is nothing new, and has been an ABYC requirement for probably 50 years. The Coast Guard picked it up from ABYC in the 80's.
     
  7. sdowney717
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    sdowney717 Senior Member

    Hi, Ike
    I still have my manual for the EggHarbor 37 boat.
    Looking at the battery schematic , I dont see an extra additional grounding joining wire mentioned, also notice the 1966 date on the drawing.

    eggharbor-battery-diagram (2).PNG
     
  8. missinginaction
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    missinginaction Senior Member

    I'm just not getting the point here.

    I've never seen a starter with an isolated ground. Maybe there are exceptions out there but every starter I've seen grounds through the block it's attached to.
    Alternators? Yes, there I often see isolated grounds but not starters.

    So lets say we have a AWG 0000 cable running from our start battery to the starter itself. The starter grounds through the block. We also have an equivalent cable running from the main DC grounding bus to the engine block. The boat's batteries, both starting and house also ground at the same DC main bus. Everything is tied together at the main DC grounding bus.

    With one engine you'd have one yellow cable (AWG 0000 in this case) going from the engine to the main DC grounding bus.
    With two engines you would have one yellow cable going from each engine to the main DC grounding bus. So two AWG 0000 each tied to the main DC grounding bus.
    Since both engines are tied to ground at the same main bus, why would another cable, between the engines be necessary?

    What am I missing here?

    MIA
     
  9. rangebowdrie
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    rangebowdrie Senior Member

    A 1961 Chris Craft 55 ft motor yacht that I work on has a ground interconnect between the two engines, and it was factory installed, as were the individual engine grounds back to the batts.
    Perhaps it may be thought of as a "belt and suspenders" arrangement, or of a way of keeping both engines at the same potential?
    Whatever,, I believe it to be good practice.
     
  10. gonzo
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    gonzo Senior Member

    VolvoPenta diesels had the starters always hot and the solenoid ground them.
     

  11. sdowney717
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    sdowney717 Senior Member

    Disconnect the ground wire to one of the engines. Then crank engine over, and see what happens.
    It might send all the starter return current through a smaller grounding wire and burn that wire, OR, due to the large voltage drop, your starter solenoid may just go click-click-click, and nothing happens. These extra wires are for a just in case failure, which AFAIK, has never happened in the last 50 years on my boat.
    Someone who is messing with the wires, might leave one loose or off accidently, wire might snap off highly unlikely though. Stuff happens.

    Other thing is for my MSW inverter, I am pretty sure if the large negative wire is not connected, the inverter does not start up, there is no internal connection maybe inside inverter between AC ground on its metal case, and the DC negative wire. So really I dont need an extra ground wire of equal to or one size smaller than the negative DC power wire. But maybe if it was a pure sine wave, I would. I dont know cause I dont have a pure sine wave inverter to look at and see if the AC case ground is internally connected to the DC negative wires. I have had to rebuild my 3000 watt inverter twice, last time I finally changed the mosfet control chip to a US made product and that solved the problem of it blowing power mosfets. The chinese version could not shut down the mosfets properly on an overload, and if they are left on when another mosfet bank turns on, it creates an internal dead short and lets out the magic smoke.

    Only way my inverter could fail and internally ground the negative wire to the case, is if one of the 6 large negative wires feeding the mosfets came loose off the connecting buss as if the bolt came apart inside. Very doubtful. That bolt is fine thread, they dont usually come loose. And if one wire came off, the inverter would either shut itself down, or internally short and let out the magic smoke. But then it is self contained to the inside of the unit.

    I also have a GFCI outlet breaker in a box right at the AC power output of the inverter, so maybe that would help, like it detects current on the ground wire and then it open circuits hot and neutral. ALL GFCI breakers open hot and neutral simultaneously, including GFCI breaker in distribution panels.
     
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