Surprised by the gauge of the 12V utility socket wires at the rear of the console

Discussion in 'Prime Accessories and Modifications' started by sylvaing, Aug 6, 2023.

  1. sylvaing

    sylvaing Senior Member

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    So I'm installing a trailer harness (to seldomly pull small load in a light aluminum utility trailer) and routed the 12V cable to the rear console 12V socket which is 12V/120W so 10A. The trailer harness module requires 12V/10A (its fuse is 10A) so that was a perfect fit. No need to bring the cable to the front of the car and have more parasitic power drain by connecting it to the battery, so I thought.

    Well, look at the size of the wires for that jack! They're allowing 10A through that???

    I'm planning on changing the trailer light bulbs to LED so they don't draw as much power as incandescent.
     

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    #1 sylvaing, Aug 6, 2023
  2. jdenenberg

    jdenenberg EE Professor

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    It is the size (gauge) of the wiring that determines the fuse capacity. The fuse is there to protect the wires. I have found the the old cigarette lighter style connectors get hot when asked to deliver more than 5 amps.

    JeffD
     
    #2 jdenenberg, Aug 6, 2023
  3. sylvaing

    sylvaing Senior Member

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    And yet, the power limit shown on the outside of the socket says 12V 120W, so 10A... Go figure.
     
    #3 sylvaing, Aug 6, 2023
  4. fuzzy1

    fuzzy1 Senior Member

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    Can you read the gauge of this wire?

    Depending on the allowed insulation temperature, I'm seeing ampacity charts allowing it to be 18, 20, or even 22 gauge. Though the later will be getting quite hot, requiring 90°C insulation.
     
    #4 fuzzy1, Aug 6, 2023
  5. sylvaing

    sylvaing Senior Member

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    Nothing is written but my wire stripper 18 gauge slides over the insulation and its 20/22 opening is a tight fit. I would say it's at max a gauge 22. It's crazy they allow 10A through that! Once I hook up the trailer next week, I'll see how hot it gets with all the lights on and the brake pedal pressed. The 12V wire that came with the harness is a gauge 16.
     
    #5 sylvaing, Aug 6, 2023
  6. ChapmanF

    ChapmanF Senior Member

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    As fuzzy1 was getting at, the ampacity of wire is influenced by what temperature the insulation can stand, and how well heat can leave the wire.

    If you pass the same current through a thinner copper conductor, there will be more heat generated, but that can be ok if the wire insulation is both higher temperature-resistant, and thinner so more heat can get away.

    Most of our judgments for how thick a wire "oughtta be" for a certain current come from experience with household wiring, most of which uses familiar types of insulation rated for 90℃.

    Car manufacturers are really looking at the weight and cost of copper the car will have to haul around, so they've gone to these ultra-thin new insulation types like GXL or TXL, which can take temperatures up to 125℃ and also be super thin. So the wire is thinner both because the copper gauge can be reduced and also because the insulation is a lot thinner around it, and the much thinner insulation lets more of the heat escape, and the temperature rise that does remain is still within the rating of the higher-temperature insulation.

    Ampacity charts that work for household wiring, or even for the old dirt-cheap PVC-insulated automotive wiring, just aren't the same charts that work for the new stuff.
     
    #6 ChapmanF, Aug 7, 2023
  7. sylvaing

    sylvaing Senior Member

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    That would make sense but what I forgot to add was those two tiny wires were within a plastic flexible conduit with electrical tape wrapped around it. You can see the wires exiting the conduit at the top of the picture. Not much place for heat to dissipate.
     
    #7 sylvaing, Aug 7, 2023
  8. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Not much, no.

    But just enough.

    This isn't an especially new trend in automotive engineering, and there's millions of wire harnesses out there with wire, connectors, anti-rattle dressings and harness looms just barely good enough to get the job done.
     
    #8 Leadfoot J. McCoalroller, Aug 7, 2023
  9. sylvaing

    sylvaing Senior Member

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    I've decided to splice through there. I've let it opened for now since the trailer is at the cottage and I'm waiting for the LED kit to replace the trailer's lights. Should be able to test it this weekend. If there is a too big voltage drop or it gets too hot, I'll need to find a way to bring it to the front of the car where the battery is. To be continued...
     
    #9 sylvaing, Aug 7, 2023
  10. sylvaing

    sylvaing Senior Member

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    Update: At the cottage and installed the LED lights to replace the incandescents one on the trailer. Hooked the cable and it stayed cool to the touch, even after 10 minutes and with the flashers On to increase the load. I therefore closed the rear of the console and that concludes this thread, for me
     
    #10 sylvaing, Aug 10, 2023
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