A cathodic protection system is a corrosion cell in which the structure to be protected is the cathode. Sacrificial or galvanic systems are corrosion cells of the differential metal type.

Sacrificial anode systems use a material that will develop a more negative voltage when coupled with the structure of concern. Typical sacrificial anode materials include aluminum, magnesium, and zinc, when any of these anode materials is coupled to steel, they behave anodically and discharge current, which is picked up by the structure, arresting the corrosion process on the structure.

Galvanic cathodic protection systems are typically used where the total current requirement is low and the total circuit resistance allows the small voltage differential between the anode and the cathode to generate the protective current. Galvanic systems can be designed to last a long life. This is achieved by adding sufficient metal to reach the desired life. These systems also have the advantage that they require little maintenance and incur no operating costs, other than preventive monitoring and maintenance.