SIRIUS Size S0 power contactor — what the ratings mean for your panel
The Siemens 3RT1023-1AN20 is a SIRIUS power contactor in the Size S0 frame, rated for AC-4 duty at 8.5 A at 400 V — that's the motor-reversing and plugging current, not the resistive-heater number. If you're switching a reversing motor or a jogging load, this is the rating that governs contact life. AC-2 at 400 V comes in at 4 kW, which covers wound-rotor or slip-ring motor starts. Screw-type terminals on both main and auxiliary circuits. Main contacts accept 2x (1...2.5 mm²) solid or stranded, up to 2x 10 mm² max. Auxiliary contacts take 2x (0.5...1.5 mm²) up to 2x (0.75...4 mm²). AWG equivalents: main 2x (16...12), 2x (14...10), 1x 8; auxiliary 2x (20...16), 2x (18...14), 1x 12. No spring-cage option on this order code — if you need push-in wiring, look at the 3RT1023-1AP00 variant. Mounts via screw and snap-on onto 35 mm DIN rail per EN 50022. Width 45 mm, height 85 mm, depth 91 mm. Side-by-side mounting allowed — no derating gap required for adjacent contactors in the same row. Pollution degree 3, so it's rated for industrial environments with conductive dust or condensation.
Coordination and short-circuit protection — don't guess the fuse
Type 2 coordination (no damage to the contactor after a short-circuit) requires a 25 A gL/gG fuse. Type 1 coordination (contactor may need replacement but the installation is safe) allows a 63 A gL/gG fuse. These are the manufacturer's assignments — using a different fuse size or type voids the coordination claim and can cause welded contacts or arc flash in a fault. Mechanical life is 10 million operations typical. That's the no-load switching endurance; electrical life under AC-4 load will be lower — factor in the switching frequency and current when estimating replacement intervals for a jogging or reversing application.
Environmental and compliance
Operating temperature range -25 to +60 °C. Storage temperature exceeds that range — the -25...+60 °C limit is for running, not shelf life. RoHS compliance date 01.07.2006, so it meets the EU RoHS cutoff. Reference code per IEC 81346-2 is Q (power switching device). Front face rated IP20 (finger-safe), terminals rated IP00 (no protection). In a standard IP54 or IP65 panel, the terminal area is inside the enclosure — the IP00 rating just means the screw terminals themselves aren't sealed, which is normal for panel-mount contactors.