What is the minimum size of the copper equipment grounding conductor when a lighting panel is protected by a 150-ampere circuit breaker?

The minimum size of the copper equipment grounding conductor is determined by the NEC (National Electrical Code) requirements, specifically Table 250.122. This table outlines the minimum conductor sizes based on the rating of the overcurrent protection device, such as a circuit breaker.

For a lighting panel protected by a 150-ampere circuit breaker, the required minimum size for a copper equipment grounding conductor is indeed 4 AWG. This size ensures that the grounding conductor is capable of safely carrying any fault current that may occur, thereby providing adequate protection against electrical shock and ensuring the safety and reliability of the electrical system.

By using a grounding conductor of the correct size, the system can effectively divert or mitigate potential electrical faults, which is essential for both personnel safety and equipment protection. Larger sizes than required could unnecessarily increase costs and complexity, while smaller sizes than required would fail to meet safety standards and could lead to dangerous situations during fault conditions.