SENTRON 3LD Main Control & EMERGENCY-STOP Switches Siemens SENTRON 3LD Main Control and EMERGENCY-STOP Switches are switch disconnectors featuring rated currents up to 250A. Siemens 3LD comes in 3-, 4-, and 6-pole versions and features 25kA to 50kA maximum short circuit. These main control and EMERGENCY-STOP switches come in various mounting types, including floor mounting, distribution board mounting, front mounting, and molded-plastic enclosures.