[Ultra-HOG]

Maybe there is just a misunderstanding somewhere. The point of placing the fuse as close as possible to the power source is to protect everything downstream, including the wire itself, from current flow in excess of the rating of the fuse. The physical location of the fuse in the circuit is critical. True, the size of the wire between a properly sized fuse or circuit breaker and the load is very important, but the physical location of the fuse is critical for similar but far different reasons. Perhaps that is where the confusion lies with this topic. Use the example of an accessory such as a small audio amplifier installed in the trunk of your car. If you were to power the device from the battery located in the engine compartment, feed it with a much oversized wire (generally a good thing to do) such as a 4 gauge wire to supply a 5 Amp device only 15 feet away, and install the fuse in the trunk just 6 inches from the amplifier, the wire between the battery and the fuse is not protected at all. If you shorted the wire to ground by running a screw through the door sill then through the wire then to the body, 100% of the current flow that the battery could produce would flow from the battery to the point of the short (the screw). Zero current would flow from the screw to the fuse. In that case the fuse would actually be connected to ground via the screw, not the battery. The wire, even a 4 gauge wire, between the screw and the battery would be so severely overloaded that it would start to heat very rapidly until it failed (burned or melted apart) or the battery itself failed (or exploded due to the direct short). Visions of the inside of a toaster come to mind.

If, in the example above, you chose to connect the amplifiers ground wire back to the negative battery terminal via another 4 gauge wire and connected the chassis of the amplifier to the vehicle body, the results would be the same. The additional problem that connecting the amplifiers ground wire to the negative battery terminal would cause is that if the vehicles main ground cable from the battery to the chassis deteriorated, corroded or simply failed, your amplifiers ground wire would have to handle the entire vehicles electrical systems current demands to and from the battery. The 40 to 60 Amp current draw that the starter motor draws when you start the engine would be more than your new ground wire could handle. Ok, a 4 gauge wire might handle it for a short period of time but a 12 or 18 gauge wire would not.



In your example of house wiring, circuit breakers or fuses are connected at the source. They are inside the electrical panel just a few inches from the main entrance cable, physically protected inside of a sturdy metal box. The entire electrical panel is 'protected' by the main breaker, usually a 200 Amp breaker, 100 Amps per phase for most modern residences. If there were no individual circuit breakers in the electrical panel and they were all at the receptacle end of the circuit, the wire in the wall would not be protected beyond the protection that the main 200 Amp breaker would provide. Only wires and devices that are downstream of the breaker itself are protected by that breaker. In this example with breakers at the receptacle end, if you ran a nail into a 12 gauge wire inside the wall before the breaker and shorted the black power wire to any or all of: the white common wire, the bare ground wire, or an earth ground connection such as you (via the nail and the hammer) or a water pipe, what would happen to the wire? I suggest that the wire would get very hot very quickly and one of two things would happen. Either the wire would melt apart, hopefully before a fire started, or, the main 200 Amp breaker would trip. In either case, the 15 or 20 Amp breaker that was at the receptacle end of the wire would have no current flow through it so it would have no reason to trip. The entire current flow would have been from the source inside the electrical panel, through that nail and either back via the white or bare wires or directly to ground, all of which are ahead of the breaker in this example. That is why the breakers are installed where they are, at the source.



It is very important to locate the fuse or circuit breaker as close as possible to the power source in order to limit the exposure of any unprotected power feed to the fuse or circuit breaker. Failing to do so can have catastrophic results.



In vehicles, never make power connections directly to the battery unless there is a fuse at the battery. An auxiliary power terminal on the fuse block is a better and a safer choice. Never make a ground or negative connection directly to the negative battery terminal, make them to the body, frame or other designated common ground point. In many of today’s vehicles that have "multiplex" wiring for factory installed lights and accessories, choosing the wrong power or ground wire to connect to can have unpredictable results. Auxiliary battery and / or large power capacitor installations for high power accessories such as high power car stereo installations require a great deal of care and knowledge if they are to be done safely and correctly.



Just my opinion, I could be wrong, but I don't think so.

Here endeth the rant...