What is the minimum ampacity requirement for the grounding conductor leading to the boat's AC grounding system?

The minimum ampacity requirement for the grounding conductor in an AC grounding system is determined by the need to safely handle fault currents that might occur during a short circuit or other fault conditions. The grounding conductor must be capable of carrying the maximum current that may flow in the system without permitting damage to the conductor or creating a safety hazard.

The requirement that the ampacity not be less than the sum of the ratings of the disconnect circuit breakers ensures that the grounding system can effectively deal with any fault conditions. This is because in the event of a fault, the total current that can flow into the grounding system may be equal to or greater than the ratings of the disconnect circuit breakers. Therefore, using the sum of these ratings for the grounding conductor provides a safe and adequate margin for any potential faults.

This approach helps to ensure both safety and reliability within the electrical system, as a grounding conductor that is too small could become overloaded, leading to overheating or even fire hazards, while a properly sized conductor will help ensure quick tripping of the circuit breakers during fault conditions.