What it is and what it does
The Siemens 3RT1026-1BG44 is a SIRIUS power contactor in the size S0 frame, designed for switching motor loads in industrial control panels. It carries an AC-4 rating of 15.5 A at 400 V, which means it can handle the severe switching duty of reversing or inching motor starts where the contacts make and break the full motor current under load — not just the run current. For AC-3 duty (normal motor start/stop), it's rated for 11 kW at 500 V and 11 kW at 690 V, covering common three-phase motor sizes across 400-690 V line supplies. The coil draws 5.4 W on DC hold — a continuous-duty coil that stays cool in a sealed enclosure, so no derating needed for the holding power.
Mounting and integration
Snaps onto 35 mm DIN rail per EN 50022, or screws directly to a backplate. The 45 mm width and 85 mm height fit standard S0 contactor spacing; the 150 mm depth leaves room for front-facing auxiliary contact blocks and the coil terminal cover. Main circuit terminals accept screw-type connections: 2x (0.5...1.5 mm²) solid, 2x (0.75...2.5 mm²) stranded, up to 2x 4 mm² max. For AWG, that's 2x (16...12) solid, 2x (14...10) stranded, or 1x 8. The front face is IP20 finger-safe; the terminal area itself is IP00 — keep fingers and tools out. Side-by-side mounting is allowed with 6 mm spacing at the side, and the ambient range is -25 to +60 °C during operation. At altitudes above 2,000 m, derate the thermal current.
Sizing and coordination
For Type 2 coordination (the standard for minimal contact damage after a short circuit), the required upstream fuse is gL/gG 35 A. For Type 1 coordination (replace the contactor after a fault), use a 100 A gL/gG fuse. These values govern your branch circuit protection design. The auxiliary contact block has 2 instantaneous contacts (NO/NC configurable). Mechanical life is rated at 10 million operations typical — that's the contactor body, not the coil or main contacts under load.