Metal pipelines used as a ground return circuit running parallel to trolley tracks must be bonded to the return circuit rail at intervals not exceeding what distance?

The correct answer is 500 feet because this distance is stipulated to ensure safety and integrity in electrical systems, particularly in mining operations where metal pipelines are utilized as return circuits. Bonding these pipelines to the return circuit rail at intervals not exceeding 500 feet is essential for minimizing potential differences in voltage along the return path, which can reduce the risk of electrical shocks and other hazards associated with stray currents.

Maintaining this maximum distance helps ensure consistent electrical conductivity and improves system reliability. Effectively bonding the systems also aids in protecting equipment and personnel, helping to prevent interference from magnetic fields and ensuring compliance with safety regulations.

The other options suggest larger intervals, which would not adhere to the preventive measures necessary for electrical safety in mining environments. Larger distances could lead to increased risks associated with poor grounding and grounding-related failures.