Where is the available fault current typically the highest in a low voltage distribution system?

The highest available fault current in a low voltage distribution system is typically found at the service point. This is because the service point is where the utility service enters the facility and is the location closest to the source of power. At this point, the impedance of the distribution system is relatively low since it has not yet encountered significant resistance from downstream equipment, wiring, or loads.

As you move away from the service point towards the load terminals, the fault current diminishes due to the additional impedance introduced by circuit breaker settings, conductors, and any connected loads. Similarly, while the transformer secondary does provide a significant fault current level, it does not exceed that available at the service point where utilities connect to the distribution system. The circuit breaker, while it is a critical component for overcurrent protection, does not maximize the fault current; rather, it is designed to limit and interrupt currents exceeding its rating.

Therefore, the service point is where the fault current is maximized, making it the correct choice.