Which of the following is NOT a power source for impressed current cathodic protection?

Impressed current cathodic protection (ICCP) systems are designed to prevent corrosion on metal surfaces by providing a protective electrical current. The power sources typically utilized for these systems include rectified commercial power, fuel cells, and renewable energy sources like wind-powered cells.

Fuel cells generate electricity through a chemical reaction and can effectively supply power for ICCP systems. Rectified commercial power indicates the process of converting alternating current (AC) to direct current (DC), which is essential for ICCP. Wind-powered cells also contribute renewable energy that can be harnessed for these protection systems.

In contrast, vacuum tubes do not serve as a viable power source for ICCP. They were primarily used in the early days of electronics for amplification and switching and do not possess the capability to generate or supply adequate electrical current needed for cathodic protection applications. Therefore, among the options listed, vacuum tubes are not associated with cathodic protection power sources, making it the correct answer.