The Siemens 3RB1015-1SB0 is an electronic overload relay from the SIRIUS 3RB1 series, rated for 3 to 12 A with Class 10 trip characteristic. It mounts directly onto a size S00 contactor (screw connection) and is configured for manual reset only — no auto-reset option on this variant. The electronic sensing gives tighter protection than a bimetal relay, especially on the low end of the range where a thermal device would drift.
The 3 to 12 A adjustment range covers fractional-horsepower motors up to about 5.5 kW at 400 V (depending on full-load current). The size S00 footprint is the smallest Siemens contactor frame; it clips directly onto the matching 3RT2 contactor, saving a DIN-rail slot and reducing wiring between the relay and the contactor coil.
Integration note
Screw terminals accept 0.5 to 4 mm² stranded or solid wire. The manual-reset-only variant (no auto-reset) is the safer choice for unattended machinery — after a trip, someone has to walk to the panel and push the button, confirming the fault is cleared. On the contactor mount, the overload relay's main power path passes through the contactor's load-side lugs; the control circuit for the contactor coil runs through the relay's NC trip contact (95-96). Verify the coil voltage matches the control voltage before wiring.