What it is and what it does
The Siemens SIRIUS 3RT2026-2BB40-1AA0 is a Size S0 power contactor with a 24 VDC magnet coil terminated via spring-type terminals. It is rated for AC-1 switching at up to 40 A and AC-3 motor duty at 18 A, making it a fit for controlling three-phase motors up to about 7.5 kW at 400 V in a standard control panel. The contactor snaps onto a 35 mm DIN rail per DIN EN 60715, or can be screw-mounted, and is designed for standing installation on a horizontal surface. Its 45 mm width and 107 mm depth fit the S0 frame footprint common across the SIRIUS line.
What the key ratings mean for your panel
AC-1 rating (resistive load) at 40 A tells you this contactor can handle heater banks or lighting loads at that current continuously. The AC-3 rating (squirrel-cage motor starting) at 18 A is the number that governs motor switching — that is the current it can make and break under starting conditions without excessive contact wear. For motor duty, the AC-3 rating is the one to size against. The 24 VDC coil pulls in at 0.8 x rated voltage and drops out reliably. The spring-type terminals accept solid or stranded wire from 1 to 10 mm², and up to 2x (0.5 to 2.5 mm²) for the auxiliary contacts. That covers most control wiring in a standard panel without needing bootlace ferrules for the main power circuit. Operating temperature range of -25 to +60 °C covers most indoor panel environments, including unventilated enclosures near process lines. The contactor is rated for 10 million mechanical operations typical, so it is built for high-cycle applications like conveyor or pump cycling.
Integration into the panel
Mounts on 35 mm DIN rail per DIN EN 60715; the snap-on feature lets you install it without tools. Required clearances: 10 mm upwards, 10 mm forwards, 10 mm downwards, and 6 mm at the side for heat dissipation and wiring access. The S0 frame size is shared across the SIRIUS contactor range, so the footprint is consistent if you need to swap in a different coil voltage or auxiliary configuration later. The spring-type terminals on the main contacts and coil mean no screw-torque verification during commissioning — strip to the correct length and push in. The auxiliary switch is built in, so you do not need a separate side-mount block for basic status feedback.