Wire resistance chart

We all know there is no such thing as a free lunch. Stranded copper wiring, which is what is typically specified for automotive use, has a certain amount of resistance per foot. This resistance per foot decreases as the gauge of wire increases (indicated by a smaller number; confusing, I know).  The figure below is the American Wire Gauge (AWG) standard for resistance of copper wire by the foot.





EXAMPLE: Installing an Electric Fuel Pump
OK, now that you know your Laws and how they apply to basic circuits, it's time to give you a rfeal world example. Let's say that you just purchased an electric fuel pump and wanted to determine what gauge of wire to use to connect it.
Here's what you should know:

• Current requirements of the pump at 12 VDC (this should be provided by the manufacturer). For the sake of this example, let's say that it's 10 amps.
• Length of wire from the ignition switch to the fuel pump--let's assume this is 20 feet since it is typically located near the fuel tank.
• Length of return path from pump ground to charging system ground--let's assume this is 5 feet (more on this later ).
• Resistance of different gauges of wiring via the supplied AWG wire resistance chart.