Safety relay for guarding circuits — SIL 3 / PL e
The Siemens 3SK1121-1AB40-1AA0 is a safety relay rated for use in safety-related circuits up to SIL 3 per IEC 61508 and IEC 62061, and PL e per ISO 13849-1, with a safe failure fraction of 99 %. The 22.5 mm wide housing mounts on a DIN rail via screw and snap-on fastening, and accepts screw-type terminals for solid (1x 20–14 AWG, 2x 18–16 AWG) and stranded (1x 20–16 AWG, 2x 20–16 AWG) conductors.
Total current through the safety relay is limited to 12 A at 40 °C ambient, derating to 6 A at 60 °C. The maximum operating frequency is 360 cycles per hour. Power loss peaks at 2 W. Mounting position is any, but observe the derating curve above 40 °C.
Switching capacity and response times
Contact ratings: 1 A at 24 V DC, 1.5 A at 115 V AC, and 1.5 A at 230 V AC. The typical response time is 30 ms, with a maximum of 50 ms; the DC-side maximum is 110 ms. The sensor input minimum pulse duration is 75 ms. Shock resistance is rated at 10 g / 11 ms.
EMC and environmental ratings
EMC emitted interference complies with IEC 60947-5-1, Class A. Overvoltage category is 3, degree of pollution is 3. Insulation voltage is rated at 300 V. The design supports cascading of multiple units.