Service conductors installed as open conductors shall have a clearance of not less than ____' from a window that is designed to be opened.

The correct answer of 3 feet for the clearance of service conductors from a window that is designed to be opened is based on safety regulations and standards to prevent electrical hazards. This distance is established to ensure that anyone opening the window does not inadvertently come into contact with the conductors. The standard clearance is crucial because it minimizes the risk of accidental electrical shock or short circuits caused by the window being opened and potentially making contact with the conductors.

In this context, the requirement acts as a protective measure, providing adequate space to safeguard individuals from encountering live electrical wires, which poses a serious danger. By adhering to this minimum clearance distance, safety is prioritized in residential and commercial building practices, creating a safer environment for both occupants and maintenance personnel. The other clearances of 2 feet, 4 feet, and 5 feet do not meet the established standard and may not adequately mitigate the risks associated with open conductors near accessible windows.