System Sensor B224RB-IV Intelligent Relay Base offers standard 4″ and 6″ bases, as well as, specialty base designs including relay, isolator, sounder, and low-frequency sounder options for Select Series detectors. The standard 4″ and 6″ bases offer a plug-in detector base intended for use in intelligent systems, with screw terminals provided for power (+ and –), and remote annunciator connections. Communication takes place over the power (+ and –) lines. The 4″ base offers a compact design while the 6″ base provides compatibility with a wider range of junction boxes.