Mobile Wiring

Discussion in 'General Technical Questions and Answers' started by KJ4QCV, Nov 11, 2009.

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  1. KJ4QCV

    KJ4QCV Ham Member QRZ Page

    Ok I'm the proud new owner of a Yaesu FT-2800 and a Larsen NMO antenna. The big brown truck should be delivering it today. Now I need to run some wires from the battery to the inside of the cab of my truck, Yaesu says use 12awg wire??? That seems barely enough as 12 awg is rated to 9.3amp and the 2800 can draw 10amp(65watt) on TX. Should I run bigger maybe 10 or 8 awg to a distribution block in the cab then connect the 12 awg that is already attached to the radio with the fuse to the block, and would it be beneficial?
  2. KX0Z

    KX0Z Ham Member QRZ Page

    You can follow Yaesu's suggestion. Although If you want to use larger wire you certainly can, it won't hurt anything. I would run the power wire directly to the battery. Make sure to fuse the + wire close to the battery, as that will protect the wire in case it shorts out to the car chassis.. What guage wire goes to the distribution block in the cab..
  3. KZ4Y

    KZ4Y Ham Member QRZ Page

    Use Heavier gauge wire


    12 Ga wire should be the minimum gauge to use. I use #4 from the battery to inside my vehicle to a distribution point (having lots of capability). I use car stereo connections for easy components available just about anywhere. Then I use 10 Gauge to my radio (an Icom 706) and 12 ga. to other sets. And for easy connect/disconnect I use Anderson Powerpole connectors.

    Gd luck with your setup.

  4. KX0Z

    KX0Z Ham Member QRZ Page

    Thats kind of what I do in my Solara. I have 8 gauge wire running into the car under the passenger seat into a brass distribution block. Then my Icom28H and my 200W car audio amplifier connect into the block.
  5. N3UJM

    N3UJM Ham Member QRZ Page

    Stop at the auto parts store and get some plastic wire loom to protect the wires. On my old truck, I made a jones strip "hot buss" under the dash protected by a 30A breaker. I wired the radio into that using the inline fuses and a bendix plug for quick disconnect.
    If I do it again I'll use Anderson PowerPole connectors. I've used them up to 40A with no problem.

  6. AD5MB

    AD5MB Ham Member QRZ Page

  7. K0RGR

    K0RGR Premium Subscriber QRZ Page

    I generally use #10 for short runs, and #8 for longer ones. But, I've certainly used #12 many times with no ill effects. A lot depends on the length of the run.
  8. K9STH

    K9STH Ham Member QRZ Page

    Connect the positive lead (red) directly to the battery using a fuse basically right at the battery connection. Ground the negative lead (black) directly to the body of the vehicle using as short a wire as possible. Do NOT fuse this lead.

    Connecting the negative lead to the body of the vehicle cuts the "IR" drop in the wiring almost in half. Also, if, for some reason, you lose the negative connection between the battery and the chassis of the vehicle you will NOT provide a path for the entire battery load (including starting the vehicle) through the negative lead to the radio.

    The major commercial two-way manufactures have been installing radios as such for many decades. The reason for both leads being long and each having a fuse is just a carry-over from the "CB" days of the Japanese radio manufacturers. In the "goode olde dayes" many tractor units (the "truck" part of "18 wheelers") were positive ground. Therefore, the radios were made so that the chassis was isolated from ground. The same radio could be used in both positive and negative ground vehicles by connecting the appropriate wire to the battery and the body of the vehicle. In a negative ground vehicle the black wire went to the body of the vehicle or the negative terminal of the battery and the red wire to the "hot" or positive terminal of the battery. In a positive ground vehicle the black wire went to the "hot" terminal of the battery and the red wire went to the body of the vehicle or the positive terminal. Basically, this meant that no matter what the polarity of the ground in the vehicle the red wire went to the positive terminal of the battery and the black wire went to the negative terminal of the battery.

    When the Japanese started manufacturing radios for amateur radio use they just continued this practice. Most commercial two-way radios made in the United States have a long red wire (positive) and a fairly short black wire (negative) which is connected to the body of the vehicle. The red lead has a fuse and the black lead does not have a fuse.

    Glen, K9STH
  9. K8ERV

    K8ERV Ham Member QRZ Page

    Sometimes it is easier and more available to run several smaller wires in parallel.

    TOM K8ERV Montrose Colo
  10. N4CR

    N4CR Ham Member QRZ Page

    What you are doing is known as Chassis Wiring. According to this, maximum amps for #12 Chassis Wiring is 41 amps.

    From that article:

    The Maximum Amps for Power Transmission uses the 700 circular mils per amp rule, which is very very conservative. The Maximum Amps for Chassis Wiring is also a conservative rating, but is meant for wiring in air, and not in a bundle.

    The larger issue that you need to worry about is voltage drop. According to this page, 15 feet of #12 at 10 amps drops around .25 volts. This is quite acceptable.

    Wire it up.
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