Phoenix Contact 2906781 A surge protection system typically consists of a protective plug and base element that integrate a status indicator and disconnect knife, designed for use with 2-wire floating signal circuits such as those with current loops between 0(4) mA and 20 mA. The system is also equipped with indirect grounding via a gas discharge tube, making it compatible with HART protocols, and can be employed in safety-related circuits that require SIL 3 certification.