In a main lug panel receiving power from a 300-Amp breaker, what is the smallest EGC that can be run?

The smallest Equipment Grounding Conductor (EGC) that can be used for a main lug panel receiving power from a 300-Amp breaker is determined by the National Electrical Code (NEC) tables. Specifically, NEC Table 250.122 provides the sizes of EGC required based on the rating of the overcurrent protection device (in this case, the 300-Amp breaker).

For a 300-Amp breaker, the code calls for a minimum conductor size of 4 AWG copper for the EGC. This ensures that the grounding system can safely carry fault current, minimizing the risk of fire or electric shock in case of a fault condition. Using a grounding conductor that is sized according to the specified NEC tables is crucial for maintaining safety and ensuring that the electrical system will operate effectively during fault conditions.

It's important to remember that while specific application requirements might lead to using different conductor sizes, the minimum EGC specified by the NEC provides the safe and reliable underpinning for electrical installations.