Siemens 3TK28060BB4 24VDC Contactor (5NO/1NC)

The Siemens 3TK28060BB4 is a high-performance DC-operated contactor belonging to the 3TK28 series. It features 5 normally open (NO) main/auxiliary contacts and 1 normally closed (NC) auxiliary contact, making it suitable for complex switching circuits in machinery and process control. The coil is rated at 24V DC, ensuring safe low-voltage control in industrial environments.

Electrical Specifications

Mechanical Construction

The contactor features a compact modular design with screw terminals for reliable wire connection. The housing is made of self-extinguishing thermoplastic (UL94 V-0) for enhanced fire safety. An integrated mechanical indicator shows contact position, and a manual override button allows for testing and maintenance without energizing the coil.

Coil and Suppression

With a low holding power consumption (approx. 2.5 W), the 3TK28060BB4 reduces heat generation in control panels. The coil is equipped with built-in varistor surge suppression to protect PLC outputs from back EMF. The pickup voltage is 80% of nominal, and dropout voltage is 20-60% of nominal, ensuring reliable operation even with slight voltage fluctuations.

Applications

This contactor is ideal for switching resistive and inductive loads such as solenoid valves, heaters, small motors, lighting circuits, and signal lamps. The 5NO/1NC configuration is particularly useful in safety circuits or interlocking sequences where multiple NO contacts are required for enabling signals and one NC contact for feedback.

Standards and Certifications

The Siemens 3TK28060BB4 complies with IEC 60947-5-1, EN 60947-5-1, and UL 508 (recognized component). It is CE marked and RoHS compliant. The operating temperature range is -25°C to +60°C, suitable for worldwide industrial environments. Storage temperature: -40°C to +80°C.

Installation and Accessories

Mounting is done via DIN rail (35mm) or screw fixing. Optional accessories include auxiliary contact blocks (front or side mount), surge suppressors, and mechanical interlocks for reversing applications. The contactor’s width is 45mm, allowing high packing density in control cabinets.

Reliability and Maintenance

Due to its silver alloy contacts, the 3TK28060BB4 resists welding and erosion, ensuring low contact resistance over thousands of cycles. Routine inspection is limited to terminal tightening and visual check of arc chutes. With no maintenance required for the coil, this contactor provides trouble-free service for years.

Conclusion

For control systems requiring multiple NO contacts and a single NC contact under 24V DC control, the Siemens 3TK28060BB4 offers a perfect balance of compact footprint, high switching reliability, and electrical longevity. It is a trusted component for PLC output expansion, panel building, and machine automation.