Simplex 2081-9028 — Isolated Loop Circuit Protector (ILCP) for Simplex circuits carrying up to 5 A.Any fire alarm conductor that leaves the building — a NAC to a detached structure, an SLC crossing a yard — sees lightning and power-line transients that will take out panel drivers. This epoxy-encapsulated protector installs where the circuit crosses the envelope and clamps line-to-line and line-to-earth in under a nanosecond, with series resistance low enough for a high-current NAC or audio run. 5 A continuous DC or audio; 38 VDC / 28 VAC RMS line-to-line, 48 VDC / 33 VAC RMS to ground 0.1 Ω/line, 68 µH/line, 0.017 µF shunt Surge 2000 A (8 × 20 µs) line-to-line and line-to-earth For DC NACs, 25 VRMS speaker circuits, IDNAC and TrueAlert SLCs 3-3/8" × 2" × 1"; 18 AWG color-coded leads; UL 497B listed This is an isolated loop circuit protector, not an overvoltage protector — for UL 864 overvoltage duty order 2081-9044, and under 200 mA order 2081-9027. Needs a dedicated 4" square metallic box.