What is a disadvantage of using an impressed current system?

The correct choice highlights a significant concern associated with impressed current cathodic protection systems. Impressed current systems use a power source to drive a current through an electrolyte, which helps to prevent corrosion on the metal structures being protected. However, one disadvantage is the potential for cathodic interference.

Cathodic interference can occur when the protective current affects nearby structures or systems, causing unintended electrochemical reactions. This could lead to the deterioration of metal that is not intended to be protected, potentially creating new corrosion issues. Therefore, while impressed current systems can effectively protect larger structures and offer more flexibility compared to sacrificial anodes, the risk of interference with neighboring metal installations is a critical drawback that must be managed.

In contrast, the other options do not accurately represent drawbacks of impressed current systems. For example, claiming that such systems require no power source is misleading since they are specifically designed to use an external source for operation. Similarly, the idea that they are limited to protecting only small structures overlooks their application in larger infrastructure, and stating that they are cheaper than sacrificial systems is not a universally applicable assessment, as costs can vary based on a range of factors.