Impressed current anodes discharge current when powered by an external DC power source. Typically, this external source is a transformer/rectifier that converts AC power to DC power. With enough external power supply units, impressed current anode systems can discharge enough current to protect virtually any structure. This is regardless of size or coating status. We do not need to choose these anodes based on their activity level. We can instead choose them based on their current discharge characteristics – how much current can they handle. The three most common impressed current anodes are graphite, high silicon cast iron, and electro catalytic type anodes.