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An excess of current is usually because an uncontrolled connection to battery voltage has occurred.
Let's talk about the most basic of circuits, a simple light bulb. You start at the battery positive, which is at 12 volts. There is a wire that goes from the positive terminal to one side of the light bulb, then another wire that goes from the other side of the light bulb to the negative terminal of the battery. As long as the light bulb is good and the battery is charged you have light.
Then, after 30 years of operation and vibration, the two wires rub together and wear the insulation off. Current now goes from the battery positive through the wire until it finds the worn insulation, then it takes the SHORT CUT into the negative wire and returns to the negative terminal of the battery, bypassing the light bulb entirely. This is where we get the term "short".
Unfortunately, aside from just rendering the light inoperative, it also damages the wires. This is because the light bulb was restricting how much current flowed through the wires. Dim lamps allow a little current, brighter lamps allow more current. Headlights allow still more current. A "shorted" circuit allows virtually limitless current, limited only by the resistance of the wires themselves, and that isn't much. So the circuit takes every electron your battery is willing to provide, overloading the wires tremendously, overheating them, and burning them.
It is for this reason that fuses exist. The power (12 volts) has to go through them FIRST.. If a short occurs, the fuse will overheat and melt long before the wires will overheat and burn.
Let's talk about the most basic of circuits, a simple light bulb. You start at the battery positive, which is at 12 volts. There is a wire that goes from the positive terminal to one side of the light bulb, then another wire that goes from the other side of the light bulb to the negative terminal of the battery. As long as the light bulb is good and the battery is charged you have light.
Then, after 30 years of operation and vibration, the two wires rub together and wear the insulation off. Current now goes from the battery positive through the wire until it finds the worn insulation, then it takes the SHORT CUT into the negative wire and returns to the negative terminal of the battery, bypassing the light bulb entirely. This is where we get the term "short".
Unfortunately, aside from just rendering the light inoperative, it also damages the wires. This is because the light bulb was restricting how much current flowed through the wires. Dim lamps allow a little current, brighter lamps allow more current. Headlights allow still more current. A "shorted" circuit allows virtually limitless current, limited only by the resistance of the wires themselves, and that isn't much. So the circuit takes every electron your battery is willing to provide, overloading the wires tremendously, overheating them, and burning them.
It is for this reason that fuses exist. The power (12 volts) has to go through them FIRST.. If a short occurs, the fuse will overheat and melt long before the wires will overheat and burn.
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