What the AC-1 rating tells you
The 3RF3340-1DA04-0KN0 is a 1-pole solid-state contactor from the Siemens SIRIUS 3RF33 family, rated for 40 A in AC-1 duty (resistive loads) at 40 °C ambient. That 40 A figure applies to resistive heating or lighting banks where inrush stays under 1.5× steady-state. For motor or transformer loads (AC-3/AC-4), the allowable current drops significantly — the part's data sheet derating curve governs that choice. The load voltage range spans 48 to 460 V AC, making it suitable for 400 V three-phase lines common in European panel builds.
Short-circuit protection and coordination
Siemens specifies this contactor as short-circuit-proof up to 25 A when protected by a B-curve miniature circuit breaker. That coordination means the MCB clears a fault before the SSR's semiconductor junction sees destructive energy — a critical detail for panel builders sizing the upstream protective device.
Control voltage and wiring
The control input is 24 V DC — a standard PLC-level signal that avoids the coil hold-in issues of AC-operated contactors. Screw terminals on both power and control sides simplify panel wiring; no special tools beyond a screwdriver are needed. The unit ships as a single piece (1 piece per package) with dimensions 105 x 27 x 122 mm, sized for a standard DIN-rail footprint alongside other SIRIUS modular components.