Wiring "Trunks"

I've read the 101 and FAQ threads, but I'm still a bit confused over how to wire the main + and ground wire that most of the bike's components will connect to.

In a stock cb350, the fuse between the battery and ignition switch is rated to 15A and connected to a 16ga wire. Max current for a 16ga wire is 7A, so why is it that the fuse is rated at over twice the maximum current?

Also if a larger gauge wire is used for the + wire, how is that it can have a higher current than the smaller wires that connect to it? I was under the impression that circuits only use as much current as the smallest wire in the circuit, as in an 18ga wire connected to a 14ga wire will only carry the current of the 18ga.






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The amount of current being used doesn't have to do with the wire, but with the components connected to it. The main trunk wires in the 350 should be 14 gauge, not 16. Check the wires that lead to the ignition switch. They're pretty hefty.

That said, wires are usually rated at a 100% duty load, so you can actually get away with thinner wires if they're not to be used 100% of the time (e.g. horn and turn signals). Also, the rating is usually a "safe" maximum rather than actual maximum. An 18 gauge wire can probably pull 20A without being damaged, assuming you're only doing it for a short period of time. Because the fuse is the weak point in the circuit, the wires will still be OK and the fuse will pop. It's still preferable to use as small a fuse as is feasible, however.