Circa 4B3S-75 5 Pin Digital Telephone Extension 5-Pin Primary Telephone Surge Protection TVSS.
The Circa Telecom 4B3S-75 is an advanced, 75V solid-state UL 497 primary telecommunications 5-pin protection module. The module fits any industry standard 5-pin building entrance protector housing. All models employ state-of-the-art silicon breakover technology as the active overvoltage clamping elements, along with PTC (positive temperature coefficient) overcurrent circuitry which allows normal Digital telephone current to pass, but quickly blocks damaging fault currents. UL & cUL listed Primary
4B3S Series PDF.