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The National Electrical Code (NEC) Table 250.66 provides important information regarding the sizing of equipment grounding conductors. It applies to the derived conductors of separately derived alternating current (AC) systems as they are essential for ensuring safety and proper grounding in electrical installations.

When considering separately derived systems, such as transformers or generators, the NEC requires that the grounding conductors be sized appropriately to ensure they provide adequate fault protection. Sizing these conductors is crucial for minimizing the risk of electrical shock and fire hazards, as they play a pivotal role in safely discharging fault currents to the ground.

The applicability of this table extends beyond just residential wiring and DC systems, as it covers a wide range of installations involving AC systems and their derived conductors. Its purpose is to promote consistency and safety in how grounding methods are approached across different electrical systems, making the understanding and usage of Table 250.66 essential for electricians working with both residential and commercial applications.