What this reversing contactor assembly does
The Siemens 3RA2316-8XB37-1DB4 is a SIRIUS reversing contactor assembly — a pre-wired pair of contactors with mechanical and electrical interlocking, so you can reverse a three-phase motor without building the interlock logic yourself. It ships with two 3RT2016-1DB47 contactors (size S00) already mounted and wired for reversing duty. That means it handles both normal starting and the more demanding reversing/inching cycles without derating the motor power. The coil is 24 V DC, which is common for PLC-controlled panels — lets you drive it directly from a 24 V DC output without an interposing relay.
Mounts on 35 mm DIN rail with either screw or snap-on fastening. You can rotate the assembly ±180° on a vertical surface, and tilt it forward or backward by ±22.5° — useful when you're fitting it into a tight enclosure and need to angle the wiring terminals toward the duct. Dimensions are 90 mm wide, 68 mm high, 145 mm deep — the depth is the main thing to check if you're fitting it into a shallow panel or a pull-box. The coil terminals use screw-type connections as well, same wire ranges. No special crimp tools needed — just a screwdriver.
Built-in surge suppression and auxiliary contacts
A varistor surge suppressor is built into the assembly across the coil — that saves you from adding a separate RC snubber or MOV when the contactor is switched by a PLC output or a relay. It clips the inductive kickback on the 24 V DC coil. Six instantaneous auxiliary contacts are available — three per direction of rotation — so you can wire feedback to the PLC or seal-in the reversing command without adding a separate auxiliary contact block. Mechanical life is rated at 10 million operating cycles typical — that's the contactor mechanism itself, not the main contacts under load. For reversing duty at rated current, the electrical life will be shorter; the AC-4 rating gives you the worst-case electrical endurance figure.
Environmental limits and compliance
The vibration resistance is specified at 10.5 g / 5 ms and 6.6 g / 10 ms for both AC and DC excitation — relevant if the panel is mounted on a machine or a moving vehicle. RoHS compliance date is July 1, 2006 — the assembly meets the original RoHS directive. Clearance distances around the unit: 6 mm upwards, forwards, downwards, and to the side; 0 mm backwards (against the DIN rail or mounting surface).