Safety relay output expansion for enabling circuits
The Siemens 3SK1211-1BW20 is a SIRIUS safety relay designed as an output expansion for relay enabling circuits — it adds isolated contact sets to an existing safety relay or safety CPU, letting you break multiple load circuits in a single safety function. Rated control supply voltage is 110...240 V AC/DC (0.85...1.1 tolerance at 50/60 Hz and DC), and the contact rating is a flat 5 A across 24 V, 115 V, and 230 V — no derating needed between those common control voltages. The 22.5 mm width and screw-and-snap-on mounting mean it clips directly onto a DIN rail in the same panel row as the upstream safety relay; the 121.6 mm depth and 100 mm height keep the footprint compact for a crowded enclosure.
The 5 A contact rating is consistent across all common control voltages — 24 VDC, 115 VAC, 230 VAC — so you don't need to swap modules when the panel uses mixed supplies. The total current maximum of 12 A is the sum through all contacts; stay under that per-module limit. The 300 ms maximum response time and 200 ms typical are fast enough for most guarding applications but not for light-curtain blanking — this is an output expansion, not a safety PLC input.
Wiring and installation notes
Terminals are screw-type, accepting solid wire 1x (20...14 AWG) or 2x (18...16 AWG). With core end processing (ferrules), the range is 1x (0.5...2.5 mm²) or 2x (0.5...1.0 mm²). The maximum operating frequency is 360 cycles per hour, which is fine for guarding doors or E-stops but not for high-speed cycling.