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Shore power back fed to the generator

Discussion in 'Generators' started by 993RSR, Jul 13, 2021.

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  1. 993RSR

    993RSR Senior Member

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    I recently bought a boat with a 5kw Northern Lights diesel gen set. Diesel generator runs well but no electricity being produced. All the breakers on the gen set look good but no power on either side of them. Then we noticed the lock out bar had been removed so the generator and shore power panel source. That mod would allow both shore & gen breakers to be on at the same time. Assuming this occurred what would fail first on the gen set or is the complete elect end toast?
  2. Capt Ralph

    Capt Ralph Senior Member

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    Not good.
    If you can not figure it out for safe operation, please get a proper tech in there.
    Pretty sure you would not like your new wire-curly hair do (at least) that may happen.

    We can try to help but with out lots of schematics (or drawings) and pictures, we may be not time achieving.

    Would you have wiring schematics for the boat and panel?
    N L info is on their web site (used to be). I have lots of N L stuff here if needed.

    Just be careful when messing with that stuff (curly)..
    Last edited: Jul 13, 2021
  3. DOCKMASTER

    DOCKMASTER Senior Member

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    How is it possible to have both shore power and gen on the buss at the same time? I get your point about a lock out bar but don’t you have a source selector in addition to breakers? If you can truly have both on at the same time, holy cow that’s dangerous. Not just your generator damage but if you are running the gen and backfeed shore power you are really asking for trouble. You can seriously hurt or kill someone and in most places is actually illegal.
  4. Pascal

    Pascal Senior Member

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    Some boats only have a safety slide over the breakers. No rotaries. Pretty bad that the boat is missing the slide. No idea what it could damage inside the gen... voltage regulator probably?
  5. 993RSR

    993RSR Senior Member

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    The lock out slider was broken off by somebody and I suspect that is what damaged the gen set.
    I am not a do-it yourselfer and always try to hire the best tech for the job. Unfortunately with the demand for service it will be 5 weeks before the NL dealer trouble shoots the gen set.
    I did buy the replacement lock out parts and installed them.
  6. MBevins

    MBevins Senior Member

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    Safe bet the generator is damaged, however any good generator guy should be able to diagnose your problem, he may not be able to readily get parts, you may have to order the parts yourself,
  7. Capt Ralph

    Capt Ralph Senior Member

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    Sounds like the shore connect would have to be disconnected first then start the gen-set.
    I assume the owner was not available to discuss this with you and no survey.

    We worked on a Meridian that had a gen-set failure like this.
    The transfer breakers and slide bar were intact, just the one of the breakers had an internal issue (carbon trail).
    While on shore power and gen-set running, the gen-set got zapped.
    Fancy newer Cummins/Oh-No.
    The voltage regulator and all else were fine.
    Just the armature exciter diodes fried.

    On another boat, smaller NL, not used for a long time and did not make juice.
    High moisture in the windings and lost it's self exciting magnetism.
    Ran the engine for a few hours and re-gauzed (flashed) the windings.

    Easy fixes.

    Hope you find an easy fix also.

    Oh, while you are repairing the transfer switches, don't forget to include a forth lead.
    Green wire open while on shore, green wire tied to white while on gen-set or inverter.
    During updates, installs and repairs we usually incorporated this into our check list.
  8. tbaxl

    tbaxl Member

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    Capt. Ralph,
    Where oh where is the green usually tied to the white for the genny?
  9. Capt Ralph

    Capt Ralph Senior Member

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    Only when off the dock.

    On a proper transfer switch (4 pole), when in the gen-set position the green and white are tied.
    While in shore power position, white and green are NOT tied.
    Here the dock service ties green and white (per code) together.

    This is how we installed gen-sets and is ABYC approved (mandated).

    There are long and boring codes from ABYC, CFRs, and other that have these specs.

    If your white and green are tied on board, while on shore service, on a newer dock with GFI service breakers, they will trip.
    You will also offer stray currents in your bonding system to/from other boats in the hood.
  10. Pascal

    Pascal Senior Member

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    N and G are bonded at the generator.

    I don’t think I have ever seen ground being switched on and off at the transfer switch. All grounds are tied together at the bus. Neutral though is switched on and off at the transfer switch though so when switching from gen to shore neutral is disconnected from the gen therefore the G to N bonding inside the gen is broken

    marine inverters also bond N to G when in inverter mode but automatically break the bond when in charging mode otherwise dockside GFI would trip. This is why you need marine inverters and not off grid or truck inverters
  11. Capt Ralph

    Capt Ralph Senior Member

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    So, when you switch to shore power, white and green are still tied? This is the usual case when GFI service breakers are tripping.
    On the gen-set, only while on gen-set away from the dock are green and white tied. NOT TIED while on shore power.
    We used a 4 pole transfer switch to make this happen. In gen-set mode, green and white are strapped..
    How do you keep green & white separate when on shore power?
  12. Pascal

    Pascal Senior Member

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    If the N from the Gen is disconnected at the transfer switch or dual breaker with slide, then the neutral from shore is disconnected from the N/G bonding in the gen
  13. Capt Ralph

    Capt Ralph Senior Member

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    But your green may still be tied to ships bonding. Also not correct.
    Green should be connected to bonding off of the shore power service also, only when on ships power.
    On shore power, green (fault current) must go to the shore service. I think we agree, separate from white.
    This is why we never trust 2 pole breakers, don't trust 3 pole breakers.
    The sure fire way to ensure all is correct, 4 pole transfer switches.
    Oh, rarely found.
    Now, those with isolation transformers with out a white wire input, most can ignore this.
    Last edited: Jul 22, 2021
  14. CaptPKilbride

    CaptPKilbride Senior Member

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    I had the same experience on a poorly wired boat. Luckily it was just the fried diodes, and it was a quick and easy repair.
  15. tbaxl

    tbaxl Member

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    Thank you very much, that may be the issue I am having here in Marathon that we talked about. Hope you and family are well.
  16. Capt Ralph

    Capt Ralph Senior Member

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    Any updates?
    What did you find?
    How was it fixed?
    Lots of pictures (we like to watch)..