Hair dryers can be used to load test a circuit breaker but that test will tell you nothing about the withstand rating. The withstand rating is determined by testing to destruction at the electrical testing laboratory. The resultant rating is on the breakers labeling.
The available fault current is determined by calculation. You need the rating and internal impedance of the transformer as well as the type size and length of the conductors between the transformer and the terminals of the device that you are concerned about.
"Calculations can be based on the source fault current at the transformer. Unless the user has fault data for the exact circuit of interest, a conservative estimate can be achieved by starting with the fault current at the site transformer. If desired, further refinement can be done by calculating current reductions due to conductor impedance. This method is most useful for smaller electrical facilities; use at larger facilities may provide overly conservative values.
The maximum fault current available at the transformer terminals is determined by the following formula, using data from the transformer nameplate, which can be supplied by the power company or a site engineer.
Secondary full load current = Single phase transformer kVA (Secondary kV) OR Secondary full load current = Three phase transformer kVA (Secondary kV)(?3) THEN
Secondary fault current = Secondary full load current x 100 Percent transformer impedance
This is the maximum fault current at the transformer, which will be reduced by conductor impedance. This reduction can be estimated using wire characteristics for various cross-sections and lengths."
The calculation of series ratings of breakers or fuses that are down stream from other Over Current Protective Devices is the kind of task that electrical engineers are paid to do.
-- Tom H