Typical Specifications Parameter Specification / Value Application Standard IEC 61643-21 (for SPDs connected to telecommunications and signaling networks) Protection Class For measuring, control, and data circuits (Type D per some classifications) Rated System Voltage (Un) 24 V AC/DC (for the FPNO-21 variant; other variants exist for 12V, 48V, etc.) Maximum Continuous Operating Voltage (Uc) 32 V AC/DC Nominal Discharge Current (In) 8/20 µs 5 kA Maximum Discharge Current (Imax) 8/20 µs 10 kA Voltage Protection Level (Up) ≤ 60 V (measured at 5 kA, 8/20 µs; exceptionally low for signal protection) Response Time < 1 ns (for the final diode protection stage) Nominal Current (Signal Circuit) 250 mA (maximum continuous load current) Line Resistance Typically 1.5 Ω (very low to minimize signal distortion) Capacitance < 50 pF (low capacitance to prevent signal integrity issues in data lines) Connection / Cross-Section Screw-clamp terminals / 0.14 - 1.5 mm² (for delicate signal wiring) Housing Material Thermoplastic (UL94 V-0) Protection Degree (IP) IP20 (when installed in an enclosure) Operating Temperature Range -40 °C to +80 °C Status Indication Visual (color change): • Green: Functional • Red: End-of-life (protection degraded and needs replacement) Mounting DIN-rail mountable (35 mm) Dimensions (H x W x D) Approx. 90 mm x 18 mm x 62 mm (standard module size) Typical Applications Protection of: 4-20 mA loops, 0-10 V sensor signals, Pt100 thermocouples, RS-485/RS-232, Profibus PA, telephone lines, alarm circuits.