How can I determine the safe width of the PCB traces so that they withstand the momentary short circuit current before the circuit breaker trips?
A fuse might be more suitable.


SMD Fuse : Current Rating   1A  , Voltage Rating - 350Vac , $0.18 @ 500pc

or a Polyfuse 1A $0.40 (500pc)  10A max  radial




The whole idea of a fuse or a breaker or a Polyfuse to choose protection that reacts quicker than the fragile path. If a short thin track heats up faster than a breaker or a polyfuse, then the only choice is a fast blow SMT fuse. got it?  Which was my 1st answer.  Ensure the track resistance is much much less than the SMT resistance, by design of the tracks and additional solder if necessary or busbar. A 2A fuse is 41 mOhm cold. 

Otherwise if you don't then the track becomes the fuse.  Beware of high resistance The whole idea of a fuse or a breaker or a Polyfuse to choose protection that reacts quicker than the fragile path. If a short thin track heats up faster than a breaker or a polyfuse, then the only choice is a fast blow SMT fuse. got it?  Which was my 1st answer.  Ensure the track resistance is much much less than the SMT resistance, by design of the tracks and additional solder if necessary or busbar. A 2A fuse is 41 mOhm cold. Otherwise if you don't then the track becomes the fuse. 
 Beware of high resistance contacts.