What it is and where it fits
The Siemens 3RT1015-2AN21 is a SIRIUS power contactor in the compact S00 frame size — 45 mm wide, 60 mm tall, 73 mm deep — designed for switching motor loads and resistive circuits in control panels. It mounts via screw or snap-on onto 35 mm standard mounting rail per DIN EN 50022, so it drops into any IEC-profile panel without adapter plates. The 24 VDC coil is the key selection anchor here. Auxiliary contact ratings are 10 A at 24 V, 2 A at 60 V, 1 A at 110 V, and 0.3 A at 220 V — these are the limits for signal-level switching, not the main poles. For motor duty, the AC-2 rating at 400 V is 3 kW, and the AC-4 rating at 400 V is 6.5 A; that tells you this contactor handles reversing or inching duty cycles, not just across-the-line starts. Spring-loaded terminals on the main circuit accept 2x (0.25 to 2.5 mm²) solid or stranded, or 2x (24 to 14 AWG). That means no screwdriver torque check on the power connections — strip, insert, done. The front and terminal areas carry IP20 finger protection, standard for enclosed panel use.
Coordination and environment
For type 2 coordination (no damage to the contactor after a short circuit), Siemens specifies a gL/gG fuse of 20 A. For type 1 coordination (contactor may need replacement after a fault), the fuse can go up to 35 A. This is the number your panel designer needs for the short-circuit protection scheme — don't guess it from the motor FLA. Operating temperature range is -25 to +60 °C, with a degree of pollution 3 rating (conductive pollution or dry non-conductive that becomes conductive). That covers most industrial environments but not clean-room or medical front-end applications without additional enclosure derating. Maximum operating altitude is 2,000 m. Side-by-side mounting is permitted, which is expected for the S00 frame — you can pack these at 45 mm pitch without derating, as long as ambient stays within the -25 to +60 °C window. The 6 mm clearance at the side is the minimum to adjacent metalwork for the magnetic field.