Agree. It's not the best way to go generally. Have made many designs with a 
fuse link track in the B+ line in hopes that a trace will blow before a hazardous 
thermal event can occur; in case someone put a penny in the fusebox or 
somesuch. We found that the allowable variance in copper thickness, plating 
thickness, trace width, and (I suppose) the operating ambient make burning a 
track off the board pretty hard to nail down.

As kinda said, all you can really do is to size the track such that the width is 
just enough under all worst case allowable conditions to keep the rise over 
ambient from causing the laminate to degrade. An inch or so seems to be 
enough skinny length.

If you need to pass 10 amps all day, under hood, in the desert sun, but need 
to protect against 15 amps, a fuse link trace is NOT the way to go. But it 
might vaporize before something *does that thing I can't say* somewhere if 
you pump 150 amps through it.

Depending on how the board ends up being mounted in the application, and 
the composition of things nearby, it can still be a pretty iffy way to go. 

Sorry for the less-than-scientific response, but that's all i gots...

Best Regards,
-Chris

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