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15 or 20 Amp Fuse?

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  • 15 or 20 Amp Fuse?

    I was told on here to use a 15 Amp fuse next to the battery in-line with my M3-ATX PSU, since that's what it's rated at, but I recently brought the car to a local audio place to have the guy there quickly redo a bit of the wiring with some switches and he said it'd be better to use a 20 Amp fuse since over the length of the wire it's going to lose a bit of voltage and draw a bit more amperage? This sounds reasonable, but I'm curious as to what you guys think?

  • #2
    As long as that fuse is still rated less than what the wire from the Battery to the M3-ATX can safely handle (based on its gauge), then you should be fine. That fuse is there to prevent that wire from overheating and causing damage to it's environment (your car). *But current at one end of a wire can't be more than at the other, unless there are other nodes on it going elsewhere.

    *Courtesy of: Kirchoff's Current Law.
    It's been a while...


    • #3
      Have a look here. About a 1/3 of the page down is a bit on wire sizes and max current draw. There is also a current calculator that calculates voltage drop across the length of the wire.
      The last thing you want is for the wire to melt and short out. If you are not sure, always use a smaller fuse than you think. Worst case is the fuse blows.
      Never let the truth get in the way of a good story