The maximum prospective short circuit current is the maximum electrical current which can flow in a particular electrical system under short circuit conditions. It is determined by the voltage and impedance of the supply system. It is of the order of a few thousand amps for a standard domestic mains electrical installation in the UK, but may be as low as a few milliamps in a SELV (Safety Extra Low Voltage or, occasionally, Separated Extra Low Voltage) system or as high as hundreds of thousands of amps in large industrial power systems.

It is of particular interest when designing an electrical installation because fuses and circuit breakers must be capable of safely breaking the flow of current in the event of a short circuit. When a large electrical current is interrupted an arc may form and if the breaking capacity of a fuse or circuit breaker is exceeded then it may not be able to extinguish this arc meaning that the flow of current will continue, possibly resulting in a fire or explosion.