Per manufacture: The RectorSeal SAFE-T-SWITCH Model SS2 is a 3/4 inch close coupled condensate drain pan overflow kit. This device detects blockages in condensate drains and interrupts the thermostat circuit, preventing flooding. It is compatible with the optional Safe-T-Gard Model SG1 condensate overflow alarm. The SS2 is typically installed on auxiliary drain pan outlets, which are often found on primary condensate drain pans.