What it is and where it fits
The Siemens 3RT7037-1AC20 is a SIRIUS S2 contactor — three main poles, normally open, rated for AC-3 switching up to 690 V. The 24 VAC coil draws 0.36 A at 50 Hz and 0.38 A at 60 Hz, with a closing power of 0.76 W DC and holding power of 0.35 W DC. It mounts on a 35 mm DIN rail per EN 50022, using either screws or the integrated snap-on clip. The front face carries IP20 protection; the terminals are IP00, meaning the connection area expects enclosure protection from the panel.
Key ratings — what they mean for your panel
The 690 V AC-3 maximum operating voltage covers 400 V and 480 V motor circuits with headroom. The auxiliary contact reliability is specified as "acceptability for PLC control (17 V, 5 mA)" — meaning the contacts are designed to switch low-energy PLC inputs without needing a separate interface relay. The contactor is rated for 800 switching cycles per hour under AC-3 duty, and 250 per hour under the harsher AC-4 (plugging / inching). Pollution degree 3 means it's suited for industrial environments with conductive contamination, typical of control panels near machinery.
Mounting and integration
The S2 frame is 55 mm wide, 112 mm tall, and 115 mm deep — a compact footprint for a 3-pole contactor at this rating. Side-by-side mounting is permitted, so you can gang multiple contactors without spacing. The mounting position allows +/-180° rotation on a vertical surface, and can be tilted forward/backward by +/-22.5°. Screw terminals accept 2x 0.5–1.5 mm² solid or 2x 0.75–2.5 mm² stranded, with the same range for finely stranded wire with ferrules. A product extension for auxiliary switches is available if you need additional N/O or N/C contacts.