What function does a "sacrificial anode" serve in underground electrical apparatus?

A sacrificial anode functions primarily by protecting underground electrical apparatus from oxidation and corrosion, particularly in environments where moisture is present. This protection occurs through a process known as cathodic protection.

In this process, the sacrificial anode is made of a more reactive metal than the metal it is protecting, which causes it to corrode preferentially. When the sacrificial anode is connected to the underground equipment, it supplies electrons to the metal it is protecting, preventing the oxidation of that metal. Essentially, it "sacrifices" itself to prevent the more valuable equipment from undergoing corrosion. This method is widely used in various applications such as pipelines and tanks to extend the lifespan of these systems by reducing the risk of failure due to corrosion.

The other options do not accurately describe the function of a sacrificial anode. Conducting electricity without resistance, increasing voltage, or insulating cables do not align with the sacrificial anode's primary role in corrosion protection.