3RB2987-2B SIEMENS

A SIEMENS BaseUnit (Basis unit) is a fundamental passive hardware component used within Siemens distributed I/O systems, most notably the SIMATIC ET 200SP series. It provides the mechanical mounting, backplane bus communication link, and electrical wiring terminals for process signals and supply voltages. By separating the electrical wiring base from the electronic I/O module, the BaseUnit enables pre-wiring of the control cabinet, clean cable management, and hot-swapping of active electronic modules without disturbing field connections or system bus communication.

Product Specifications

• Rated Operating Voltage: 24 V DC nominal, with support for up to 120 V DC / 230 V AC depending on the specific model type.

• Current Carrying Capacity: Up to 10 A per internal self-assembling potential group (power bus).

• Connection Technology: Push-in spring-cage terminals supporting conductor cross-sections from 0.14 mm² to 1.5 mm² (AWG 26 to AWG 16).

• Terminal Configurations: Available in 16-terminal standard configurations, supporting 2-wire, 3-wire, or 4-wire field device connections, with options for integrated AUX (auxiliary) terminals.

• Potential Grouping: Offered in light-colored versions (opens a new potential group and feeds external 24 V DC power) and dark-colored versions (forwards the potential bus from the left adjacent BaseUnit).

• Mounting Method: Standard 35 mm DIN rail mounting with integrated backplane bus connectors.

• Operating Temperature: -30°C to +60°C for standard operation, with extended temperature ranges available for SIPLUS extreme variants.

• Protection Class: IP20 protection according to IEC 60529, designed for installation inside control cabinets.

Key Product Advantages

• Pre-Wiring Capability: Field cables can be completely wired and tested before the electronic modules are installed, significantly accelerating cabinet construction and commissioning.

• Tool-Free Push-In Technology: Spring-loaded push-in terminals allow fast, vibration-proof wire insertion without requiring special tools, reducing installation time.

• System Hot-Swapping: Electronic I/O modules can be replaced under live power while keeping field wiring intact and maintaining backplane communication across the rest of the station.

• Automatic Mechanical Coding: Integrated coding keys ensure an electronic module cannot be inserted into an incompatible BaseUnit type once a module has been attached for the first time.

• Integrated Potential Bus: Automatic self-assembling voltage supply buses eliminate the need for external bridging wires between adjacent modules, creating a clean and space-saving cabinet layout.

Important Operational Considerations

• Light vs. Dark Unit Placement: A light BaseUnit must always be used at the beginning of each potential group to feed in power, while dark BaseUnits can only follow a light BaseUnit or another dark BaseUnit within the same supply group.

• Current Limitation: Total current consumption across all modules in a single potential group must not exceed the maximum rating of 10 A to prevent overheating of the internal bus.

• Proper Stripping Length: Stripping field wires to the correct recommended length (8 mm to 10 mm) is critical to ensure proper contact and avoid exposed live conductors.

• Module Alignment: Ensure the BaseUnit is securely snapped onto the DIN rail and interlocked with neighboring units before plugging in electronic modules to prevent pin bending.

• Enclosure Requirements: Due to its IP20 rating, the BaseUnit must be housed inside an enclosure rated at least IP54 or higher when deployed in dirty, humid, or explosive industrial environments.

Industrial Applications

• Machine Building: Simplifies control panel assembly and reduces wiring errors for high-volume automated machinery and packaging equipment.

• Process Automation: Deployed in chemical, water treatment, and food and beverage facilities where modular I/O expansion and continuous operation are critical.

• Automotive Manufacturing: Applied along assembly lines and robotic cells to handle high-density digital and analog sensor/actuator field signals.

• Energy and Utilities: Integrated into sub-distribution panels, power generation controls, and HVAC automation systems for reliable field signal processing.