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Untinned 50amp Marinco shore cable failure

Discussion in 'Technical Discussion' started by Pascal, Dec 17, 2011.

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  1. Pascal, Dec 17, 2011
    #1
    Pascal

    Pascal Senior Member

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    Recently experienced an odd shore power cable failure... 8 year 50amp Marinco untinned cable in a glend.

    I often check the plug and cable for heat and one night i noticed the plug was cool but the cable was slightly warm. Followed the cable to really hot spot 15' from the end.

    Turned out the white conductor, neutral, was completely melted with burned/corroded copper visible.

    No heat damage at the plug
    Never overloaded or tripped dock side breaker
    Never dunked the plug in the 3 1/2 years I have been on the boat
    No damage to exterior insulation
    Always routed loosely out of the water
    No sign of moisture on the back side of inlet and cable master

    After replacing the entire cable, I noticed all four conductors are black from one end to the other. I sent pictures to marinco tech who say they have never seen this. They ve asked that I send them damaged sections.

    I just don't understand how corrosion could have progressed thru the entire cable

    I was also very surprised to see that the cable was untinned. Don't know if it was supplied by Glendining or by the builder.

    Them when i ordered replacement tinned Ancor cable from port supply, they supplied untinned marinco. I ended up getting tinned cable from Ward

    I had no idea that corrosion could creep 80' up a cable, and had no idea that marinco and posaibly Glendining would use untinned shore cable

    Lesson learned!
  2. NYCAP123, Dec 17, 2011
    #2
    NYCAP123

    NYCAP123 Senior Member

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  3. RER, Dec 17, 2011
    #3
    RER

    RER Senior Member

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  4. NYCAP123, Dec 17, 2011
    #4
    NYCAP123

    NYCAP123 Senior Member

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    :eek: Looked at the content not the posters. He gets around. Guess those link won't help him much.:eek:
  5. T.K., Dec 17, 2011
    #5
    T.K.

    T.K. Senior Member

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    I don't think it's corrosion. Conductor insulation becomes weak and brittle with time and 8 years is not a short time. The cable load capacity decreases and normal electrical loads become over loads and the weakened insulation cannot withstand these loads anymore. I think the conductor insulation inside your cable was not very effective and you had an electrical short inside the cable which burnt the conductors.
  6. Pascal, Dec 17, 2011
    #6
    Pascal

    Pascal Senior Member

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    Insulation of the 4 inner wires is like new ( except in the heat damaged section) no breaks or cracks or it or damage to the outside yellow insulation.

    Heat damage was the result of increases resistnce due to corrosion.

    I ve seen plenty of cables that are much older than the one.
  7. NYCAP123, Dec 17, 2011
    #7
    NYCAP123

    NYCAP123 Senior Member

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    Possibly a spot where the cable once got pinched?
  8. Capt J, Dec 20, 2011
    #8
    Capt J

    Capt J Senior Member

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    This is what it sounds like to me......either the cable got pinched, caught in the glenndenning at that spot or run over by a golf cart.
  9. Marmot, Dec 20, 2011
    #9
    Marmot

    Marmot Senior Member

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    Accordiing to Pascal; One wire suffered from localized overheating and all the wires are blackened with corrosion. The insulation is in good condition and there is no damage to the outer jacket.

    Pinching a wire does not create high resistance unless it breaks conductors or stretches them enough to reduce their cross section. Anything that would do that to a single conductor in a multiconductor cable would do it to others and would create a visible effect on the jacket.

    Someone stepping on the cable probably puts more load per unit of area on a cable than a golf cart running over it.

    All the indications point to corrosion and localized work hardening at an area where the cable might be expected to endure constant flexing due to boat movement. Each strand of cable that breaks reduces the current carrying ability of the wire and increases the resistance as it increases the mechanical load that conductor has to handle when the cable flexes. Once that sequence starts it goes downhill quickly.

    It was an old cable that worked in a nasty environment. I don't think spending a great deal of additional money on tinned wire is going to make much difference in cable life. I would rather invest in a good megger and ohm meter and test the cable on a routine basis to correct connector issues when they are found. As the IR trends downwards, start thinking about replacing the cable before it becomes an issue or a threat.