How can you determine the optimal fault current for a circuit?

As per IEC definition (603-02-25), fault current is the current flowing at a given point of network resulting from a fault at another point of this network.

Fault current refers to the flow of electrical current that occurs when a fault or abnormality, such as a short circuit or ground fault, creates an unintended low-impedance path for electricity in an electrical system. This sudden surge of current can be significantly higher than the normal operating current and is typically detected and managed by protective devices like circuit breakers and fuses to prevent damage to equipment or infrastructure and ensure the safety of the electrical system.

Determining the optimal fault current for a circuit involves conducting a short-circuit analysis to calculate maximum potential fault currents. Consider system parameters, component ratings, and safety standards to ensure that protective devices can handle faults safely. Ensure compliance with industry codes and standards while periodically reassessing as the system evolves.

Fault current is a generic term that is refers to the abnormal current that may be due to Short Circuits, Overload, Earth Leakage .etc Each situation mentioned above is different and can not be generalized.

Trip really fast! If you want to limit fault energy on transmissions systems, this is what you need to do. Get 2 cycle breakers, direct trip or use goose and use a 87 device ( for T-Line POTT schemes are fast, but you can’t use them on PLC, so if you have fiber, go 87L). You could use traveling wave tripping (SEL T401) for super fast. You can be out the door in under 3 cycles. Cut your BF time down if it’s a stability thing as well. And use IPO breakers to minimize 3 pole BF to a single pole. On distribution, don’t parallel TR, install line inductors on feeders. SLG mag can be controlled by transformer ground Z being added. Note that internally adding Z in the line comes at a cost ( energy loss and voltage drop)

Limiting fault currents in electrical systems involves several methods. Current Limiting Reactors introduce impedance to restrict fault current flow. Increasing overall system impedance using resistors or reactors helps reduce fault current magnitude. Protective devices like circuit breakers and fuses interrupt circuits during faults, preventing excessive currents. Transformers with limited short-circuit capacities and selective coordination of protective devices also limit fault currents. Employing a combination of these methods is common to ensure effective fault current limitation, safeguarding equipment and system integrity.

Current limiting reactors , current limiting fuses , Fault current limiters (FCL) .etc However if you ask me, the best approach to limit fault current is through System Design and load flow studies. The modern Power System Designer , someone like myself uses softwares, the likes of ProDesign , ETAP .etc to simulate a fault condition and predetermine the fault currents in any network.

Also you need to calculate the heat dissipation in electrical enclosure Overheating may cause the devices, fuses, relays to get faulted

Three Primary options to reduce a short circuit current 1) Selection of Transformer Impedance. (Shall be kept on the higher side without negative tolerance) 2) Current limiting Reactor 3) Selection of cable length and parallel conductor. Secondary element helps to shorten the rise of short circuit current which are 1) Breaker 2) Fuse 3) Protection relay