What it is and what it does
The Siemens 3RT1026-1BF40 is a SIRIUS power contactor in the size S0 frame, designed for switching motor loads in industrial control panels. The 110 VDC coil pulls in at 5.4 W and holds at the same power, so the coil drive circuit needs to supply that continuously — no power-save circuit inside this model. Rated motor power hits 11 kW at 400 V in AC-2 duty (slip-ring motors, moderate overloads) and the same 11 kW at 500 V and 690 V, which covers most European-standard motor ratings up to that frame. For AC-4 reversing or plugging duty the thermal current limit is 15.5 A at 400 V — that is the number to size against for high-inertia loads or frequent reversals. General-use switching (AC-12) is rated at 10 A maximum, so it can handle resistive or lightly inductive control loads up to that current. The auxiliary contact block is configured as 0 instantaneous contacts — this is a main-pole-only contactor; add a separate auxiliary block if you need N/O or N/C feedback to the PLC.
Mounting and wiring
Mounts via screw or snap-on onto a 35 mm DIN rail per DIN EN 50022. The 45 mm width and 85 mm height fit a standard S0 slot in a panel layout. Side-by-side mounting is permitted with zero gap — no derating needed for adjacent contactors if ambient stays within the -25 to +60 °C operating range. Main circuit terminals are screw-type, accepting solid conductors from 2x 0.5 mm² up to max 2x 4 mm², and stranded from 2x 1 mm² up to max 2x 10 mm² (AWG equivalents: 2x 16-12 solid, 2x 14-10 stranded, 1x 8). Strip length and torque are standard for S0 screw terminals — no special tooling needed. Front face carries an IP20 rating — safe for finger-probe access in an enclosure. The terminal area itself is IP00, so the contactor must live inside a panel that provides the overall IP rating. Pollution degree 3 means it tolerates conductive dust and occasional condensation, typical for factory-floor cabinets.
Short-circuit coordination and protection
For Type 2 coordination (no damage to the contactor after a short circuit) the required upstream fuse is gL/gG 35 A. For Type 1 coordination (contactor may need replacement but the circuit is cleared) a 100 A gL/gG fuse is allowed. Sizing the fuse to Type 2 keeps the contactor reusable after a fault — worth specifying if the panel is hard to access for replacement.
Lifecycle and sourcing
The auxiliary contact rating table covers DC switching at 24 V (10 A), 60 V (2 A), 110 V (1 A), and 220 V (0.3 A), plus AC at 230 V (6 A) and 400 V (3 A). Mechanical endurance is rated at 10 million operations typical, so it holds up in high-cycle applications like conveyor interlocks or packaging machinery.