120 VAC mystery

Discussion in 'Powerboats' started by StewartG, Mar 26, 2009.

  1. StewartG
    Joined: Mar 2009
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    Location: S.F. Bay Area

    StewartG New Member

    I just joined up, initially to ask this question though I'm hoping to think of something else to contribute.
    Q: A customer of mine (at a marina in the US) recently had a meltdown at his AC neutral connection strip, 120 VAC 30A, because he overloaded his panel with electric heaters and none of the breakers tripped (23 year old trawler, Taiwan built). The mystery for me was that the outlets affected by melted wire tested as having swapped their hot and ground (green safety wire). But half the outlets were okay, even though there's only one breaker for all of them. As I disassembled the neutral strip, the outlets went to a simple open neutral condition, as one would expect. When the strip was replaced and damaged wire ends repaired, conditions returned to normal at all outlets. At no time did the panel ground strip show voltage, nor was current flowing (i.e., a short) that the meter could detect. Methinks there may be other damage, but I cannot find any, nor does the customer want me to begin tearing his conduits apart. Is there any way the positive and grounds can swap, other than from damaged or incorrect wiring? And why would half of the outlets remain unaffected, even when all their grounds were ganged at the same strip? Sorry for all the questions; I'm still scratching my head over this one. Either I was fooled, or my tester was, or both of us.
     
  2. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Is the vessel consistantly wired Y or Delta? Were the effected outlets split between shorepower and ships service? New and original?
     
  3. Boston

    Boston Previous Member

    the issue could have been in an appliance that shorted out and fed current to the ground system
    ask the customer if there are any appliances that no longer work since the event
     
  4. StewartG
    Joined: Mar 2009
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    Location: S.F. Bay Area

    StewartG New Member

    I guess it's wired Y--I'm only just learning about Y and Delta wiring. Power comes to the boat in the normal fashion, a shorepower cord, passes to a selector switch for Generator or House, then to a main breaker the ship's service panel, and from there to branch circuit legs. Both the neutral and safety wires are ganged at strips a foot or so away from the circuit breakers. All outlets are original, with no GFCI protection. As far as I know, no appliances failed when the meltdown occurred. While there is evidence of marginal DIY work here and there, the original wiring is not too bad. I couldn't find any evidence of either a ground or line fault, though there is much wiring I couldn't inspect. It looked like a simple overload/meltdown. I never tested the ground/hot swap for its load-carrying ability, was afraid I'd cause another meltdown. And as curious as I am about the cause, the customer is out of $$ and it's a Pandora's Box of liabilities I'm hoping not to open again.
     
  5. Boston

    Boston Previous Member

    well I got home wiring down to an art but I suspect your systems aboard ship are far more complex than that
    so rather than steer you wrong Im just going to read along
    best
    B

    guy named Rick W. in here somewhere seems pretty good with electronics
    might try and find him
    B
     
  6. alan white
    Joined: Mar 2007
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    Location: maine

    alan white Senior Member

    The odd thing is the meltdown occurring at the neutral strip. It sounds more like a short circuit, where a hot wire contacted the strip. If the hot wire involved was overloaded but the breaker failed to operate, it would have possibly melted that hot wire's insulation near the connection to the breaker, allowing the bare copper to contact the neutral strip.

    As far as swapping hot for ground on some of the outlets, you don't mention neutral, but obviously if the hot and (green) ground were reversed, nothing plugged into those outlets would ever have worked, since neutral and ground are both grounds. If the neutral and the hot were reversed the outlets involved would have worked fine, with polarity reversed. A recent thread discussed this, where such a condition on a boat would be very dangerous because of proximity to water.
    Are GFIs involved, by the way?
     
  7. Jack Daniels Eq
    Joined: Aug 2008
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    Location: Phuket

    Jack Daniels Eq Shockwave

    My nickel is manifold -
    You appear to be unqualified to do any troubleshooting, even less repair work
    The boat sounds like a typical Rube Goldberg Framus - garage sale components
    Anything you do will be wrong & might even contribute to, plus liability looms
    Anyone could have swapped leads. cord, polarity anytime - nobody would know or confess for fear of liability to existing marina, boats wiring.
    Walk away ...... he clearly has no money either
    BR>Jack
     
  8. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    A frequent problem is the white (neutral) and green (ground) are joined somewhere inside the boat,

    They can ONLY be joined at the source , so joined at the gen set or inverter is fine , but on board from the dock wiring is not.

    Take a look at the selector between the shore , inverter and noisemaker and see what you have.

    Its not as "Yachty" but we use plugs and sockets to transfer loads , no fires yet, or burnouts from a bad dock setup.

    FF
     
  9. Jack Daniels Eq
    Joined: Aug 2008
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    Location: Phuket

    Jack Daniels Eq Shockwave

    This post get scarier by the mo .....
    Please cease & desist
    BR>Jack
     
  10. Boston

    Boston Previous Member

    in my biz electrical issues cause the most fires and although Ive done more than my share of elec work Ild have to second Mr Daniels previous
    you staring at a can of worms that could explode at any moment
    and on your dime
    part of being a good business man is knowing when to walk away

    best
    B
     

  11. StewartG
    Joined: Mar 2009
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    Location: S.F. Bay Area

    StewartG New Member

    Thanks all, for your comments, even Jack Daniels' rather backhanded attempts. The mystery will have to remain due to reasons mentioned in my first post. But to answer some of your queries, no, there were no GFCIs involved, and as much as I had to time to search, no other damage or incorrect wiring to be seen. And so there must be either a hidden connection somewhere, or damaged wires unseen. I've run across older Taiwan boats where hidden sub panels were added by the manufacturer that were unprotected by any breaker or fuse at all. This is one of those boats where the only intelligent solution is a complete rewire.
     
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