You want the traces to be able to handle a near short circuit condition that's under the trip point on your fuses. In the case of the 11A PTC fuses that's roughly 22A. A lot of the calculators out there assume that you have an ideal board with the amount of copper you ordered on all traces. In an ideal world you would get that. In the real world a trace that's at 2/3 the spec is a much more likely case. That's even more true if you are buying boards from a low cost / quick turn outfit. They forecast one number for an inner layer and another for an outer layer. That assumes you have air able to get to the outer layer. If you have a connector on one side of the board, and the other side against a mounting plate .... not so much...
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