What this SIRIUS compact starter does
The Siemens 3RA6400-2CB43 is a SIRIUS compact starter — a direct-on-line motor starter that integrates a contactor, overload relay, and IO-Link communication into a single 45 mm wide device. It is designed for continuous operation per IEC 60947-6-2, meaning it handles steady motor loads without derating for intermittent duty. The 24 VDC coil (rated 24 V) draws a maximum of 2.9 W, which is the holding power you need to budget for in your 24 VDC control supply. The headline rating here is 4 A at 400 V AC (AC-3 motor switching), which translates to 1.5 kW (2 hp) motor capacity at 400 V. At 460/480 V it handles 2 hp, and at 575/600 V it goes up to 3 hp. That 4 A figure is the AC-3 rating — the current it can switch under motor-start conditions — not the resistive (AC-1) rating, which would be higher. For a 4-pole induction motor around 1.5 kW at 400 V, this is the right fit. The adjustable trip class (Class 10 and 20) means you set the overload relay's thermal memory to match the motor's start profile. Class 10 for fast-starting fans and pumps; Class 20 for high-inertia loads like conveyors or crushers that take longer to accelerate. That adjustability saves stocking two separate overload relays.
IO-Link and connectivity
This compact starter speaks IO-Link at COM2 (38.4 kBaud), which is the standard rate for most IO-Link masters. It does not support AS-Interface — that is a different protocol variant in the SIRIUS family. The IO-Link interface gives you access to the device's three status LEDs, parameter settings (trip class, current rating), and diagnostic data (thermal load, number of starts) directly through your IO-Link master. No separate analog or digital input card needed for the motor data. The main circuit connection is plug-in without terminals — meaning the power wiring uses a separate connector system, not screw terminals on the device body. The control wiring accepts 2x (0.25 to 1.5 mm²) solid or stranded conductors. That is typical for spring-cage or push-in terminals on the control side; verify your ferrule size if using stranded.
The 45 mm width means it takes two standard 22.5 mm module positions. Any mounting position is allowed, but vertical on a horizontal DIN rail is the recommended orientation for convection cooling. Dimensions: 191 mm high, 45 mm wide, 165 mm deep — check your enclosure depth, especially if using a shallow 200 mm panel. Vibration resistance: 4 to 5.8 Hz at 15 mm amplitude, then 5.8 to 500 Hz at 20 m/s² for 10 cycles. Shock resistance: 60 m/s² (6g) for 10 ms, 3 shocks per axis. That covers most machine-mounted applications without additional damping.
For a BOM line that specifies the 3RA6400-2CB43, the fit is confirmed by the 24 VDC coil, the 4 A AC-3 rating at 400 V, and the IO-Link COM2 protocol. The adjustable trip class (10/20) gives you flexibility across different motor loads without changing the part number.