short circuit level

Please see companion thread.

The breaking current of the circuit protective device(s).

It's actually the other way around. It depends on the fault current that can be delivered by the power supply. The circuit protective devices are then selected accordingly.

"fault level" or "short circuit level" - commonly used terms to describe (or quantify) - the current delivered by the source (at the service potential) when a "short circuit" occurs. assuming that the "short circuit" is zero impedance, it shall be the current delivered by the source with only the source internal impedance and connecting conductor impedance in the circuit. since the source and conductor impedance is very low, the short circuit current, aka fault current, is very high.

protective interrupting devices are specified (selected / rated) to withstand the high fault current for some specified duration. for LV systems the duration is 1 second under most common codes and standards. sometimes 3 second ratings are also considered depending on the specific conditions and applications.

specification of switchgear also details whether it is required to merely interrupt the circuit on fault or to also leave the switchgear usable for next use in next fault. therefore many different fault conditions and usage conditions are required to be ascertained before selecting the devices.

most modern systems designers always consider peak short circuit levels as well as prospective short circuit levels and limit the actual fault current flowing through the system by interrupting the fault in short time (in effect limiting the "let through" energy).

for actual application details a knowledge of the location (town/county/country) is also required since local rules need to be complied with in addition to national standards and electricity supply company rules.

i hope this helps.