The Siemens 3RT7027-1AC20 is a size S0 three-pole contactor with a 24 V AC 50/60 Hz coil. It switches three main poles — all normally open — and accepts an add-on auxiliary switch block. Screw terminals on both main and control circuits.
Holding power on DC is 0.24 W, closing power 0.72 W. That matters for transformer sizing in a control panel: a 24 V AC control transformer feeding several contactors needs to handle the inrush, not just the hold. Mechanical switching rates: 800 operations per hour maximum under AC-3 duty, 250 per hour under AC-4. AC-4 is plugging or inching — frequent make-break on locked-rotor current — so the lower limit reflects the heavier arc duty. For a conveyor motor starting once a minute, AC-3 at 800 1/h is fine; for a jogging station, stay under the AC-4 ceiling. The auxiliary contact circuit is rated 6 A at 230 V, 3 A at 400 V, 1 A at 690 V. That covers pilot-duty signalling through the full line voltage range. The contacts are verified for PLC-level reliability — no wetting-current problems with 17 V / 5 mA logic inputs. That puts it in the standard industrial environment class — no special clearance or creepage derating needed for most panel builds.
Side-by-side mounting is allowed — no mandatory gap between contactors on the rail. Dimensions: 45 mm wide, 85.5 mm tall, 91 mm deep. That 45 mm width is one standard 9 mm module increment — five modules wide — so it occupies five positions on a DIN-rail terminal block layout. The depth includes the coil terminals; allow clearance for screwdriver access. Wire range: 2x (0.5 to 1.5 mm²) solid or stranded, or 2x (0.75 to 2.5 mm²) finely stranded with ferrule. That covers most control wiring up to 2.5 mm². The screw terminals are the same type on main and auxiliary circuits — one tool, one torque setting.