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What amperage in this wire?

  1. Jul 18, 2011 #1
    My cars factory wire diagram is not that helpful - If a wire is feeding a terminal block that supplies 12v to a 20amp circuit (power windows) and the other is a 30amp circuit (A/C), and the possibility exists for both circuits to be drawing max amperage, shouldn't that main supply wire be able to carry 50amps? If so, what gauge wire should I use? (8 or six?)

    Thanks folks! :)
  2. jcsd
  3. Jul 18, 2011 #2


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    Staff: Mentor

    Why are you re-wiring your car?
  4. Jul 18, 2011 #3
    It's my 40 year old 70 Lincoln Mk III...and I had a relay blow and I can't find any literature on what was the amperage rating of the relay. Also, the previous owner of the car replaced a lot of the wiring in the engine compartment due to a small engine fire. So I'm not 100% sure the supply wire is even the correct gauge.
  5. Jul 18, 2011 #4
    I would use 6-gauge. If you don't know exactly how it works, better to play it safe.

    I've (re)wired cars before, and one thing I can tell you is that the material protecting it is just as important as the electrical ratings. It will likely have to endure water, high temperatures, bits of salt and dirt hitting it occasionally. Make sure you buy stuff that is designated for use in engine bays.
  6. Jul 18, 2011 #5


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    Most of the time neither circuit will draw near what it is protected with for a fuse. It's of course always wise to play it safe. Especially in automotive, where there is only 12 volts to start with. Losing X volts in a residential circuit on a 120 volt supply due to voltage loss when passing 10 amperes is one thing. But 10 amperes flowing in the same wire on a 12 volt system will drop just as much voltage and we have less to start with.
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