What this contactor is and what the ratings mean
The Siemens 3RT2337-3XF40-0LA2 is a 4-pole traction contactor in the SIRIUS 3RT2 series, frame size S2. Its headline rating is 110 A in AC-1 duty at 400 V and 40 °C ambient — that's the resistive-load current it can make and break continuously, which governs its use in heater banks, lighting, or non-inductive distribution circuits rather than motor starting. The solid-state operating mechanism means the coil is driven electronically, not by a plain electromagnet; it draws a lower hold current and the integrated varistor suppresses the back-EMF spike on dropout, so you don't need an external suppression module on the coil wiring.
Terminal configuration and wiring
Main circuit terminals are screw-type, sized for the 110 A path. Control and auxiliary circuit connections use spring-loaded (cage-clamp) terminals — strip length and ferrule sizing follow standard practice for 0.5–2.5 mm². The auxiliary contact block is built in: 1 NO + 1 NC. The coil is rated 110 V DC with an operating range of 0.7–1.25 × Uc, so it holds in from about 77 V to 137 V DC. Below 77 V it drops out reliably; no free-wheel diode needed because the varistor handles the inductive kick.
Where it fits in a panel
Frame size S2 mounts on DIN rail or panel plate. The package dimensions are 145 × 85 × 144 mm — allow clearance above and below for the spring-loaded terminal access. The 4-pole configuration suits three-phase plus neutral switching in resistive loads, or two-pole paralleling for higher current on a single phase. For motor loads, check the AC-3 rating on a different variant; this one is specced for AC-1 duty.