The Siemens 3RT1900-1SB50 is an identification-label kit for the SIRIUS contactor and motor-starter range: 19 frames, each holding 20 self-adhesive labels sized 20 x 9 mm in pastel-turquoise. It is a marking accessory — no electrical function, no switching duty. The labels fit the transparent label holders on SIRIUS devices (contactors, overload relays, auxiliary switch blocks) so the panel builder can tag each component with its circuit designation.
Each frame holds 20 labels; the 20 x 9 mm size matches the standard label window on SIRIUS contactors and auxiliary blocks.