The supplemental grounding electrode for a metal water pipe electrode is permitted to be bonded to which of the following?

The supplemental grounding electrode for a metal water pipe electrode is correctly permitted to be bonded to the grounded service-entrance conductor. This practice enhances the grounding system's effectiveness by ensuring that the grounding electrode system is adequately tied to the overall electrical system. The grounded service-entrance conductor provides a reliable reference point for the grounding of the electrical system, helping to maintain safety and reduce potential differences that can lead to electrical shock hazards.

The other choices may not provide the same level of grounding system integrity or may not be compliant with electrical codes. For example, bonding to an equipment grounding conductor is intended for equipment and not for creating a path to ground for the overall service. A lightning protection system, while crucial for safety, is designed for different purposes and might not serve the everyday grounding needs of electrical systems. Lastly, while bonding to a ground rod electrode could potentially enhance the grounding system, it may not be as effective as bonding directly to a grounded service-entrance conductor, which is typically at the same potential as earth ground and assures a lower impedance path for fault currents.