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Chassis Wiring - How Many Amps?

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  • Chassis Wiring - How Many Amps?

    OK, get your Lucas replacement smoke ready . . .

    The stock A harness is all 16ga. Does this mean a 20 amp load will burn it up?

    I was helping a friend swap out a dead alternator on his modern and he commented about how the 100 amp alt was connected with "only" an 8ga output lead. Most car guys seem to magically defer to house wiring rules of thumb for gauge vs. amps. He thought it should be at least 3ga, like the feeds to a 100A breaker box in a house. That's not the only game in town, there are lots of factors involved.

    Here's a few other differing views on ampacity.
    Caveat Utilitor.

    Mechanical engineering 101: If you put an adjustment knob, screw, bolt, or tolerance specs on something, some people will immediately fiddle with it. If you mark it DO NOT TOUCH everyone will mess with it.

  • #2
    It can get confusing when you figure AWG and SAE for the same gauge wire have two different values. The length of the wire and if it is in a bundle also affects the value one uses.


    • #3
      The load / amp capacity of a wire at 12 volts DC is much less than at 110 Volts AC assuming the same % of loss of voltage. The chart below shows the ratings for no more than a 3% loss. A 12 ga wire 15' long can carry 10 amps at 12 volts DC. There are a lot of factors in the calculation, however to keep it simple the higher the voltage the smaller the wire size can be to carry the amp load.


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