Siemens 3RT1075-6SP36 SIRIUS Power Contactor

The Siemens 3RT1075-6SP36 is a SIRIUS class power contactor designed for heavy‑duty motor switching applications. Rated for 200 kW at 400 V (AC‑3 duty), this contactor can handle motor currents up to 400 A. It is built with a 24 V DC coil and includes two normally open and two normally closed auxiliary contacts (2 NO + 2 NC). The 3RT1075 series is part of the SIRIUS 3RT family, known for high reliability, compact size, and long electrical life. This contactor is suitable for switching large three‑phase motors in compressors, pumps, fans, conveyors, and industrial machinery. It can be used with appropriate overload relays (e.g., 3RB20 or 3RU21 series) for complete motor starter applications.

Technical Specifications

Rated operational current (Ie): 400 A (AC‑3, 400 V). Motor power (AC‑3): 200 kW at 400 V, 250 kW at 500 V, 315 kW at 690 V. Rated insulation voltage (Ui): 1000 V. Rated impulse withstand voltage (Uimp): 8 kV. Short‑circuit protection: 1000 A fuse (gG) or circuit breaker. Coil voltage: 24 V DC. Coil inrush power: 300 W (typical), holding power: 10 W. Built‑in auxiliary contacts: 2 normally open (NO) and 2 normally closed (NC). Mechanical life: 10 million operations. Electrical life (AC‑3): 1.2 million operations. Dimensions: 200 mm (H) × 165 mm (W) × 210 mm (D). Weight: approx. 8 kg. Operating temperature: -25°C to +60°C. Storage: -50°C to +80°C. Protection rating: IP20 (finger‑safe terminals).

Key Features

• 400 A continuous current rating, 200 kW motor capacity at 400 V

• 24 V DC coil with low holding power (10 W) for energy efficiency

• Integrated auxiliary contacts: 2 NO and 2 NC

• High short‑circuit withstand capability (up to 1000 A fuse)

• Force‑guided contact design for safety applications

• Compact size relative to power rating

• Easy front‑mounted or screw‑type terminals

• Compatible with a wide range of accessory blocks (overload relays, suppressors)

• CE, UL, CSA certified, RoHS compliant

Construction and Operation

The contactor uses a double‑break main contact system with silver‑based contact tips for high conductivity and arc resistance. The magnetic drive system features a DC coil with an electronic coil interface that provides wide voltage tolerance (0.85 to 1.1 × Us). The coil is protected against voltage spikes by an integrated varistor (for AC) or freewheeling diode (for DC). The contactor has a built‑in mechanical indicator to show whether the main contacts are open or closed. The auxiliary contacts are mechanically linked to the main contact system (force‑guided), making them suitable for use in safety circuits. The contactor is designed for AC‑3 duty (starting and stopping of squirrel‑cage motors during running). For AC‑1 resistive loads, the current rating is higher.

Applications

The 3RT1075-6SP36 is used in heavy industrial applications such as large compressors (air, refrigeration), pumps (centrifugal, submersible), fans and blowers (large HVAC systems), conveyors (mining, bulk material handling), shredders and crushers, and metal forming presses. It can be used as a main contactor in motor control centers or as a direct switching device for motors up to 200 kW. The 24 V DC coil allows direct interface with PLC outputs without intermediate relays.

Installation and Wiring

The contactor is designed for screw mounting (using M8 bolts) on a backplate. It can also be mounted on a DIN rail with an optional adapter. Install the contactor with adequate clearance (minimum 50 mm above and below) for heat dissipation. Connect the main power lines to the line terminals (L1, L2, L3) and motor leads to the load terminals (T1, T2, T3). Torque terminals according to the value specified on the contactor (typically 40 N·m for main terminals, 2 N·m for auxiliary). Connect the 24 V DC coil to terminals A1 (+) and A2 (-). The coil is polarity sensitive. The auxiliary contacts are accessible on the front: NO contacts at 13‑14, 23‑24; NC contacts at 11‑12, 21‑22. Use appropriate wire sizes (up to 240 mm² for main conductors).

Coil Operation and Protection

The DC coil incorporates an electronic interface that reduces the holding power after the contactor picks up, minimizing heat generation and energy consumption. The coil pick‑up time is approximately 40 ms, drop‑out time is 30 ms. The coil has built‑in overvoltage protection (freewheeling diode). However, when switching the coil with a PLC output, an external diode may still be recommended to protect the output transistor. The coil voltage range is 20.4 V to 26.4 V DC.

Maintenance and Diagnostics

Visually inspect the contactor annually for signs of overheating (discoloration of terminals) or excessive dust. The contactor has a long electrical life, but after many operations the contacts may erode. If the contactor chatters or fails to pick up, check the coil voltage and the auxiliary contact circuitry. The contactor is not user‑serviceable; replace the entire unit if the main contacts are welded or the coil fails. The mechanical life indicator (often a counter) may be present on larger contactors; if not, keep a log of switching cycles.

Conclusion

The Siemens 3RT1075-6SP36 SIRIUS power contactor is a robust solution for switching large motors in industrial applications. Its 400 A rating, 200 kW capacity, and 24 V DC coil make it suitable for integration into modern PLC‑controlled systems, providing reliable and efficient motor control.