towerMAX DS-CO from ITWLinx features digital station set and central office line protector with Auto-Resetting Technology, which protects up to 2-pairs digital/analog station lines. The PTC resistors open when a surge occurs, protecting your equipment. Unlike other fuses, the PTCs close again once the surge passes. The unit offers expandable system protection using towerMAX Series Base Units. They also feature Signal Perfect Circuitry for auto-resetting surge protection for data networks, telephone and coax lines with RJ-11/45 termination type.