What it is and what it does
The 3RT1936-1ER02-ZX90 is a SIRIUS surge suppressor — a diode combination without LED, rated for 24 V DC, designed to clip the inductive kickback from a contactor coil when the DC supply is switched off. It mounts onto SIRIUS contactors in Size S2 and S3 frames.
Where it goes and why it matters
This suppressor snaps onto the coil terminals of a Size S2 or S3 contactor inside a control panel. On a DC-switched coil, the diode provides a freewheeling path that prevents the voltage spike from reaching the PLC output or DC supply — a standard fix-it-where-it-sits solution when a line-down report flags a blown 24 V output card.