Siemens 3RT5045-1AC20 SIRIUS Contactor

The Siemens 3RT5045-1AC20 is a 3-pole SIRIUS contactor from the 3RT5 series, designed for switching three-phase motors and other loads. It has a rated operational current of 125 A (AC-3 at 400V) and can control motors up to 75 kW at 400 V (AC-3). The coil is rated 24 V AC (50/60 Hz), making it suitable for low-voltage control circuits. The contactor includes one normally open and one normally closed auxiliary contact as standard. It is suitable for use in industrial motor control centers, pumps, compressors, and fans.

Technical Specifications

Rated current (Ie): 125 A (AC-3 at 40°C). Motor power: 75 kW at 400V, 90 kW at 500V, 110 kW at 690V. AC-1 resistive current: 150 A. Rated insulation voltage (Ui): 1000 V. Impulse withstand voltage (Uimp): 8 kV. Coil voltage: 24 V AC (50/60 Hz). Coil inrush power: 300 VA, holding power: 25 VA. Auxiliary contacts: 1 NO + 1 NC (integrated). Electrical life: 1.2 million operations (AC-3). Mechanical life: 10 million operations. Dimensions: 162 mm (H) × 77 mm (W) × 142 mm (D). Weight: 1.9 kg. Operating temperature: -25°C to +60°C. Terminal type: screw terminals (main: up to 95 mm²). Certifications: CE, UL, CSA, CCC, RoHS.

Key Features

• 125A AC-3 rating for 75kW motor control at 400V

• 24V AC coil for low-voltage control systems

• Integrated 1 NO + 1 NC auxiliary contacts

• Compact design for frame size S6

• High mechanical and electrical life

• Compatible with overload relays (3RU51 or 3RB30)

• Screw terminals for reliable wiring

Applications

The 3RT5045-1AC20 is used for starting and stopping large motors, controlling heating loads, and switching power in industrial panels. Typical applications include compressors, pumps, fans, crushers, and conveyor systems.

Installation

Mount the contactor on a 35 mm DIN rail or screw it directly to a backplate. Connect the three-phase mains to L1, L2, L3 and the motor to T1, T2, T3. Connect the coil to terminals A1 (24V AC line) and A2 (neutral). The coil is polarity insensitive. Add an overload relay (e.g., 3RU5146) directly on the output side for motor protection. Use appropriate wire gauges (up to 95 mm² for main terminals). Ensure correct torque (e.g., 35 N·m for main terminals).

Maintenance

Periodically check for burnt contacts or excessive noise. The contactor is maintenance-free under normal conditions. If the coil fails or contacts weld, replace the contactor.

Conclusion

The Siemens 3RT5045-1AC20 SIRIUS contactor provides reliable switching for high-power motors and loads. Its 24V AC coil and high breaking capacity make it suitable for industrial control applications where low-voltage control is required.