An AFCIs primary purpose is to prevent fires and property damage by detecting arcs that are serious enough to cause a short circuit. Electrical currents flow in a wave of distinct peaks and valleys. A variation from this pattern is considered an arc. Some arcs are harmless but others can lead to a serious problem. AFCIs are used to distinguish between small arcs such as those that occur when plugging in or unplugging an electrical device represented by a spark and more serious ones that can lead to a fire. An AFCI responds immediately to dangerous changes in the electrical current to avoid damage to the branch circuit.