What it is and what it does
The Siemens 3RT1026-1BD40 is a SIRIUS power contactor in the size S0 frame, designed for switching motor loads in industrial control panels. It mounts via screw or snap-on onto 35 mm DIN rail per EN 50022, fitting a 45 mm wide slot — standard for a three-pole contactor in a motor starter lineup. Rated 11 kW at 400 V in AC-2 duty (slip-ring motors, reversing starts), it also carries 15.5 A in AC-4 (plugging, inching). At 500 V and 690 V the motor power holds at 11 kW, so it handles the same load across common European supply voltages. The 24 VDC coil draws 5.4 W closing and holding — a single DC supply can keep it sealed without an economizer circuit. Auxiliary contacts switch up to 10 A at 24 V, 6 A at 230 V, and 3 A at 400 V, covering pilot-duty and PLC interface needs.
Mounting and wiring
Screw terminals on the main circuit accept 2x (1 to 2.5 mm²) stranded or 2x (2.5 to 6 mm²) solid, max 2x 10 mm² — enough for the 11 kW motor feed without a separate terminal block. Auxiliary terminals take 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²), max 2x 4 mm². Side-by-side mounting is allowed with 6 mm spacing at the side, so you can gang multiple contactors on the same DIN rail without derating — useful for a multi-motor conveyor zone or pump panel. Pollution degree 3 means it's rated for industrial environments with conductive dust or condensation. IP20 on the front protects against finger contact; the terminals themselves are IP00, so the panel enclosure must provide the overall IP rating. Operating temperature from -25 to +60 °C covers most indoor plant-floor conditions.
Protection and coordination
For Type 2 coordination (no damage to the contactor after a short circuit), use a gL/gG fuse rated 35 A. For Type 1 (contactor may need replacement after a fault), a 100 A fuse is allowed. The 3RT1026-1BD40 also carries an AC-12 rating of 10 A for resistive loads. Maximum operating altitude is 2 000 m without derating; above that, air density reduces the dielectric and cooling capacity. The reference code per DIN EN 81346-2 is Q (power switching device).