What It Is and Where It Fits
The Siemens 3RT7027-1AN20 is a S0 frame size contactor in the SIRIUS family, with three main poles and three normally-open main contacts. It is rated for AC-3 and AC-3e duty up to 690 V maximum, making it a direct fit for switching three-phase motor loads in control panels. It mounts on a 35 mm DIN rail per DIN EN 50022 using the screw and snap-on method, and the mounting position allows ±180° rotation on a vertical surface plus ±22.5° tilt forward and backward. At 45 mm wide, it slots into a standard panel without special spacing.
Key Ratings and What They Mean for Your Build
The AC-3 rating at 690 V means this contactor handles the inrush and breaking of squirrel-cage motors up to that line voltage. The 690 V insulation voltage rating confirms it's suitable for 400 V and 480 V systems with headroom. Its auxiliary contact circuit is rated 6 A at 230 V, 3 A at 400 V, and 1 A at 690 V — so the same set of contacts can switch pilot duty loads across different control voltages. The IP20 protection on both the front and the terminals means it's safe for finger contact inside an enclosed panel but not for washdown environments. The operating temperature range of -10 to +55 °C covers most indoor industrial environments, and the storage range of -25 to +70 °C handles shipping and warehouse conditions. Pollution degree 3 means it's rated for conductive pollution typical in industrial atmospheres.
Wiring and Coordination Notes
Both main and auxiliary/control circuits use screw-type terminals. The main circuit accepts solid or stranded wire: 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) per clamp, and the same range applies for finely stranded wire with ferrules. This is typical for a panel wireman working with standard control cable. For Type 2 coordination (no-weld after fault), the required upstream fuse is a gL/gG NH 3NA: 50 A. For Type 1 coordination (welding allowed but no fire risk), the same fuse type is rated 125 A. This matters when you're coordinating selectivity upstream in a distribution board. The magnet coil draws 0.72 W on closing and 0.24 W holding at DC — low enough that a standard 24 VDC PLC output or relay can drive it directly without an interposing relay in most cases.