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6 AWG wire melt down

Discussion in 'Technical Discussion' started by Pascal, Jul 16, 2021.

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  1. Pascal, Jul 16, 2021
    #1
    Pascal

    Pascal Senior Member

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    Has a nasty surprise on my boat today... as I walked past the main panel i smelled something. Didn’t take me long to swing the panel open and find a 6 AWG wire with melted insulation.

    it was a 4 year old Ancor tinned wire, connecting one of the 50 amp line from the back of the shorepower inlet to the panel main breaker. I don’t have an inlet breaker since the wire run is about 18 inches between the inlet and the panel main breaker.

    The other line and neutral are fine. That wire wasn’t chafing against anything, no corrosion or water intrusion. No idea why it failed.

    I used 6 AWG when i wired the panel since that’s what the 120/240-50 cord uses but I m going to replace all three with 4 AWG.

    I wonder if the somewhat tight radius affected the wire integrity

    for the time being I had enough slack to cut the end, and crimp a new terminal

    Attached Files:

  2. mapism, Jul 16, 2021
    #2
    mapism

    mapism Senior Member

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    Loose terminal maybe? From your photo it looks like the overheating might have started from it.
  3. Norseman, Jul 16, 2021
    #3
    Norseman

    Norseman Senior Member

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    Agree..
    Not marine grade tinned wire?
    Looks like plain copper strands on the picture.
  4. Pascal, Jul 16, 2021
    #4
    Pascal

    Pascal Senior Member

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    Nope. Terminal was tight and as I said this is Ancor brand tinned marine wire! I only used tinned wire when I re wired the boat and every terminal has shrink tubing, even behind regular outlets

    looks like the tin burned up
  5. Capt J, Jul 16, 2021
    #5
    Capt J

    Capt J Senior Member

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    It wasn't crimped properly. The crimp was loose, that's why the terminal looks perfect where it screwed on the panel, but fried aft of the terminal.
  6. Capt Ralph, Jul 16, 2021
    #6
    Capt Ralph

    Capt Ralph Senior Member

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    I downloaded the pic and blew it up. Nothing wrong with that crimp. A failure in the wire.

    I have discovered thru the years. A nick, scratch or stretch on the insulating cover that would allow any environment into the wire, will effect the wire one day.
    You may have had that day.
  7. Pascal, Jul 16, 2021
    #7
    Pascal

    Pascal Senior Member

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    Crimp was and is still solid. Because of space constraints I had to bend the terminal so the wire could come in without chafing on anything.

    the failure was in the wire about 1” from the terminal. The heat shrink is split in the picture because I moved the wire and bend it to test the crimp.

    I m pretty sure there was no nick in the insulation and the panel is inside the boat with no moisture.
  8. MBevins, Jul 16, 2021
    #8
    MBevins

    MBevins Senior Member

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    I made my living as a master industrial electrician, I can tell you without a doubt the connection from the wire to the connector failed. Usually due to poor crimp, don't sweat it, it happens. Replace and move on.
  9. Capt Ralph, Jul 16, 2021
    #9
    Capt Ralph

    Capt Ralph Senior Member

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    But the crimp, shrink over the crimp did not burn. Just a bit away from the crimp, it got hot.
    Where a bend and possibly abused sheath was.

    Oh well, Ship happens. Replace and move on.
    Replace the whole lead.
  10. Pascal, Jul 16, 2021
    #10
    Pascal

    Pascal Senior Member

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    Going to replace the 2 hots and N with 4awg. But I just pulled on wire, it s not coming out of the terminal. It wasn’t the crimp
  11. Capt J, Jul 16, 2021
    #11
    Capt J

    Capt J Senior Member

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    The crimp could have been tight, but it might not have had enough surface area contacting the wire to carry the load. Also make sure your loads are balanced on L1 and L2.
  12. Pascal, Jul 16, 2021
    #12
    Pascal

    Pascal Senior Member

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    No it s tight with maximum possible contact. Loads are pretty balanced since most of them (both chillers and pumps) are 240. That’s about 35 amps. The rest is split evenly between the 5 air handlers plus one charger and house loads incl the other charger.
  13. DOCKMASTER, Jul 17, 2021
    #13
    DOCKMASTER

    DOCKMASTER Senior Member

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    I just had near identical issue on my boat. One of the wires melted about 1” from the terminal where it connects to the shore power breaker in my main panel. I had my electricians pull all new wires back to the incoming j-box/fuse box and replace both port and Stbd breakers as precaution. I think my wire got damaged/overloaded when we were running big heaters earlier in the spring to heat the cockpit deck to install flexiteak. That’s the only thing I can think of that caused my issue.
  14. mapism, Jul 17, 2021
    #14
    mapism

    mapism Senior Member

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    It might feel and look solid, but still be not good enough from an electrical standpoint.
    In fact, when in my previous post I suggested a loose terminal, I meant loose on the crimping point, because the metal around the hole looks clean, while the crimped bit looks like it wasn't tightened with the correct tool.
    Ref. the insulation melted just a bit away from the terminal, the reason could well be that the connected and tightened terminal offered some heat dissipation on that side, while on the wire side there was nothing but the wire itself to take the heat.
  15. Slimshady, Jul 17, 2021
    #15
    Slimshady

    Slimshady Senior Member

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    Crimps are always the area where resistant increases. Use a highway as an analogy. 6 lane road narows to 2 lanes that are under construction for only 100 ft then back to 6 lanes again. Traffic and resulting tempers flare in this area. Difference is the amount of cars passing the construction area per minute is greatly reduced, in the wire the cars per minute must stay the same. SO tempers flare!! Melted wires!! Just swap cars for electrons and you have burnt wires. Another reason solder is recommended.
  16. Pascal, Jul 17, 2021
    #16
    Pascal

    Pascal Senior Member

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    The only heat dissipation on the terminal would have been the breaker and it shows no sign of heat whatsoever.

    solder on marine terminal? I don’t think so
  17. Oscarvan, Jul 17, 2021
    #17
    Oscarvan

    Oscarvan Senior Member

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    I thought it was not recommended in vehicles/boats because of vibration leading to fatigue failures....?
    MBevins likes this.
  18. Slimshady, Jul 17, 2021
    #18
    Slimshady

    Slimshady Senior Member

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    It's not recommended but from an electrical resistance perspective it's much better than crimps
  19. Capt J, Jul 17, 2021
    #19
    Capt J

    Capt J Senior Member

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    No, the large surface area of the terminal, allows the heat to disapate, much like a heat sink. You could have a strong crimp, where the wire is never going to pull out of the terminal, BUT the crimp is not a lot of surface area to carry the load. This is what I think went on here. But I think you're better off with 4 awg anyways. I don't think the bend has anything to do with it.
  20. Pascal, Jul 17, 2021
    #20
    Pascal

    Pascal Senior Member

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    I don’t know.... when using the correct size terminal, which was the case here, the wire fits snugly in the terminal with full contact all around.

    the shrink tube on the terminal doesn’t show any evidence of being burned or melted
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