Reversing contactor assembly — two contactors in one package
The Siemens 3RA2318-8XB30-2BB4 is a SIRIUS reversing contactor assembly — a pre-wired pair of 3RT2018-2BB42 contactors in a single housing, mechanically interlocked so only one closes at a time. This is the standard way to reverse a three-phase motor without external interlock wiring. The 24 VDC coil uses spring-type terminals — no screwdriver needed for the control wiring.
Size S00 — panel footprint and mounting
Size S00 contactor frame: 90 mm wide, 84 mm high, 83 mm deep. Clearance to adjacent components: 6 mm upwards, forwards, downwards, and to the side; 0 mm backwards (the back of the assembly sits flush against the mounting surface).
Termination and wiring — spring-loaded main and coil
No re-torquing needed on thermal cycles — the spring maintains contact force. Mechanical life is 10 million operations typical. Maximum switching frequency in AC-3 duty is 750 operations per hour — adequate for most reversing applications like conveyors, hoists, and door drives where the cycle rate stays well below one start every five seconds.
Duty ratings across voltages
Rated power varies by line voltage: 3 hp at 200/208 V, 5 hp at 220/230 V, 10 hp at 460/480 V and 575/600 V. Current ratings: 14 A at 480 V, 11 A at 600 V. The AC-4 rating (plugging / inching duty) at 400 V is 5.5 kW — lower than AC-3 because of the higher thermal stress during reversing under load. Shock resistance: 11.4 g for 5 ms and 7.3 g for 10 ms in both AC and DC axes — the assembly survives typical industrial vibration and impact without contact bounce.