The Siemens 3RT7027-1AP05 is a size S0 contactor with three normally-open main contacts, rated for AC-3 switching up to 690 V. At 230 V it handles 6 A; at 400 V it handles 3 A; at 690 V it handles 1 A. The 690 V insulation voltage and 6 kV surge resistance mean it's comfortable on 400 V line-fed motor circuits with decent transient margins. Coil draw is modest — 0.82 W closing, 0.24 W holding at DC — so the control transformer or PLC output doesn't need oversizing. The auxiliary contacts are rated for PLC-level signals (17 V, 5 mA), which means you can wire the feedback directly into a 24 VDC digital input without a dry-contact relay in between.
Mounting and integration
Mounts via screw or snap-on onto 35 mm DIN rail per EN 50022. The S0 footprint is 55 mm wide, 85.5 mm tall, 91 mm deep — fits standard panel layouts. Side-by-side mounting is allowed, so you can gang multiple contactors without a gap. Mounting position is flexible: ±180° rotation on a vertical surface, plus ±22.5° tilt forward/backward. That helps when the panel layout forces an odd orientation. IP20 on the front and at the terminals — finger-safe, but not sealed. Keep it inside a cabinet; no washdown exposure.
Coordination and protection
For type 2 coordination (no weld risk on a short circuit), the recommended backup fuse is a gL/gG 50 A NH 3NA. For type 1 coordination (allow contactor replacement after a fault), go up to 125 A. That's the fuse sizing the designer needs to lock in before the panel gets built. Rated for pollution degree 3 — conductive pollution or dry non-conductive that becomes conductive due to condensation. Typical for industrial control panels not in a climate-controlled room.