In the schematic shown here (on the left), the AC-CS safety resistor is being used to limit inrush current. The ohmic value should be carefully chosen to avoid dissipating too much power while being large enough to limit inrush current. When the MOV is short-circuited during a fault condition (as shown in the top right image), the mains voltage 115V_AC or 230V_AC appears across the safety resistor, drawing a high current and eventually fusing the resistor. This creates an open circuit (as shown in the bottom right image). In this design, the resistor helps to protect the other circuit sections during a voltage surge, all without creating a flame, spark or explosion.