Linking two devices powered by separate AC sources can create the potential for a ground-loop surge - a damaging electrical condition that can destroy your computer and wipe out data. But a Black Box ® Opto-Isolator interrupts that lethal pathway by completing the connection between the two devices with an internal fiber optic link. Data signals, converted to light pulses inside the Isolator, continue along on the circuit. But the fiber optic air gap stops ground loops from wreaking havoc with your hardware. Our High-Speed Opto-Isolator protects devices with 115.2-kbps serial ports up to 1000 feet (304.8 m) on either side of the interface. If the interface doesn''t provide enough power, order the optional 120-VAC Wallmount Power Supply (PS1002).