The third function relates to product safety and is to act as a fuse in the event of an internal fault leading to an overload condition. This requirement may be handled by a separate fuse in series with the line input resistor, but if the resistor is a fusible type, meaning that it has a guaranteed fusing characteristic under overload conditions, then the separate fuse may be eliminated. Furthermore, some resistors are also UL recognised, giving a simple one component solution for UL approved products. Note that the requirement to fuse and the need for withstanding surges can be contradictory, and careful design selection is required to achieve both properties.