What the ratings mean for fit
The Siemens SIRIUS 3RT2027-1AP04-ZX95 is a size S0 power contactor rated 27 A at 480 V in AC-3 duty — that's the motor-switching current for a 3-phase induction motor up to roughly 15 hp at 480 V. AC-3 is the standard for starting and disconnecting squirrel-cage motors under load, so this rating governs the real-world motor branch circuit, not the resistive AC-1 number. The contactor carries a maximum mechanical life of 10,000,000 operations typical, with AC-3 electrical endurance at 750 operations per hour maximum — enough for frequent cycling on conveyors or pumps without derating the duty cycle. The coil termination uses screw-type terminals, and the main power circuit accepts solid or stranded wire from 1 to 10 mm². For fine-stranded or dual-wire connections, the terminal also accepts 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²). The contactor itself is 45 mm wide, 85 mm high, and 141 mm deep — that depth is the dimension behind the panel, so a 150 mm deep enclosure is the practical minimum for clearance.
Panel integration and mounting
Mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 60715. The mounting position allows +/-180° rotation on a vertical surface and can be tilted forward/backward by +/-22.5° — useful for tight gland-plate layouts. Clearance requirements: 10 mm upwards, 10 mm downwards, 10 mm forwards, and 6 mm at the side. The 141 mm depth means the contactor body extends well behind the DIN rail; plan for at least 150 mm enclosure depth to leave room for wiring and air circulation. Operating temperature range is -25 to +60 °C; storage range is -55 to +80 °C. The AC-3 switching rate of 750 operations per hour maximum is the thermal limit for the main contacts under motor load — exceeding it accelerates contact wear, especially on AC-4 reversing or inching duty, which is limited to 250 operations per hour.
Coordination and auxiliary contacts
This variant ships without an auxiliary switch block. If your circuit requires a mirror contact or a signaling contact for the PLC, you will need to add a separate auxiliary contact block (Siemens 3RT19 series) that clips onto the front of the contactor. The main contact torque specification is 16 to 8 Nm — verify your screwdriver setting; over-torquing can strip the terminal threads on the S0 frame.