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Thread: Electrical Fire caused by shorted 7-wire cord

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    Electrical Fire caused by shorted 7-wire cord

    Good day fellow Heartlanders,
    Posting this tread for your info.
    While dry camping this past weekend, we experienced a fire caused by the 7 prong 12 volt electrical cord,
    I store my cord up inside the 5 th wheel tongue on my unit and have since it was new in 2012 with no issues.
    On Sunday I reached up and hung cord down getting ready to hook up,I went to back of unit to do other items and could smell electrical burning.
    Looked around unit and noticed smoke coming out from under nose of unit, ran up and electrical cord and metal box with all 12 volt wires on fire, managed to extinguish quickly but it burned 5 wires and cord about 6 in long. The electrical cord was shorted out against clamp going into box,melted clamp completely and part of box, electrical cord remains powered even when dry camping because of your batteries.
    Upon inspection I noticed the cord was wore at the point of entry into the metal box,this wearing was caused from continuous flexing when turning unit over the years..
    Maybe worth taking a minute to look at your cord for wear.

  2. Print this Post   #2
    Moderator danemayer's Avatar
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    Re: Electrical Fire

    Not having the umbilical cord plugged into the tow vehicle, I believe the only powered wire into the junction box would be the emergency breakaway circuit. It must have shorted to the frame or box. But that alone should not have started a fire.

    At the battery end of the breakaway wire, I think there is an automatic 12V mini-circuit breaker that would trip in the event of a short. It should have tripped, reset after a few seconds, and tripped again, and again. The fire indicates something is wrong at that end.

    You should inspect for presence of that breaker and if you don't have one, add one. if you do have one, you should assume it's no longer able to trip and it needs to be replaced.


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    Re: Electrical Fire

    - - - Updated - - -

    Thanks for the information,I’ll check out asap

  4. Print this Post   #4
    Prolifically Gabby Member JohnDar's Avatar
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    Re: Electrical Fire

    There is an excellent thread on replacing that crappy metal box with a plastic one, along with a coiled cord and a holder for the plug. Jesstalkin’ I believe was the author. I replaced mine per his tutorial.


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    Senior Member mlpeloquin's Avatar
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    Re: Electrical Fire

    I do not think that the break away switch has a fuse or breaker. It defeats the purpose of the last resort to apply the breaks when a trailer or fifth wheel would break loose. Nothing should be between the battery/power source and the breakaway switch or the breaks.
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    Re: Electrical Fire

    Quote Originally Posted by mlpeloquin View Post
    I do not think that the break away switch has a fuse or breaker. It defeats the purpose of the last resort to apply the breaks when a trailer or fifth wheel would break loose. Nothing should be between the battery/power source and the breakaway switch or the breaks.
    I understand your point, but it's a choice of which safety issue to live with. With no breaker, if the wire shorts in between battery and switch, and there's no breaker, the trailer may burn to the ground and you could be in it. With a breaker, a double failure would have to occur for someone to be injured or killed by the trailer. The hitch would have to fail and the breaker would have to fail.

    So to me, it's a single failure scenario versus a double failure scenario. I think Heartland has been installing breakers for a while. But of course I could be wrong.


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    Re: Electrical Fire caused by shorted 7-wire cord

    The no. 4 pin is +12 volt.
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    Moderator danemayer's Avatar
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    Re: Electrical Fire caused by shorted 7-wire cord

    Quote Originally Posted by TedS View Post
    The no. 4 pin is +12 volt.
    Forgot about that one. Pretty sure that one has a circuit breaker too.


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    Senior Member Flick's Avatar
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    Re: Electrical Fire caused by shorted 7-wire cord

    Quote Originally Posted by TedS View Post
    The no. 4 pin is +12 volt.
    Absolutely. That is your rv / truck charging circuit. Will have whatever voltage your rv currently has or that your converter is putting out.
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    Re: Electrical Fire caused by shorted 7-wire cord

    Actually, I added a 25 amp self-resetting circuit breaker just downstream (towards the trailer battery) of the umbilical termination box on the tow vehicle charging line of my 2008 Bighorn due to the fact that my 30 amp towed vehicle charging circuit fuse in my 2004 Dodge Ram 3500 kept blowing intermittently, with no indication to me that my trailer was no longer getting battery charging voltage while travelling. This has been in place over 2 years, and the truck fuse has not blown since then.

    I thought this configuration to be the best compromise in ensuring that my trailer's battery system was getting charging voltage while travelling. The breaker size was selected to give the best possibility of the trailer self-resetting breaker tripping before the truck fuse blows.

    BTW, when I park the trailer, I simply drape the umbilical cord over the hitch, with the 7 way connector hanging downward to keep water out of it. This doesn't put any stress on the umbilical cable at the interconnect box.
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