ABB TU849 Termination Unit for Redundant TB840/TB840A ModuleBus Modem

Product Overview

When a critical process demands uninterrupted ModuleBus communication, the ABB TU849 termination unit (3BSE042560R1) provides a robust foundation for redundant modem configurations. Designed to host two TB840/TB840A Optical ModuleBus Modems, this passive module termination unit (MTU) ensures single I/O connectivity while maintaining dual power supply paths for each modem. Its mechanical keying system prevents incorrect module insertion, and a rotary switch allows cluster address selection from 1 to 7. The TU849 is purpose-built for applications where non-redundant I/O must be paired with redundant modems, offering a compact, DIN-rail-mounted solution that simplifies installation and maintenance.

Key Technical Specifications

The TU849 operates on a 24 V d.c. power input with a range of 19.2 to 30 V, consuming a maximum of 2.5 W. It distributes ModuleBus current up to 1.5 A at 5 V and 1.5 A at 24 V. The unit accepts solid wires from 0.2 to 2.5 mm² and stranded wires from 0.2 to 2.5 mm² (24–12 AWG), with a recommended torque of 0.5 Nm. Rated insulation voltage is 50 V, and dielectric test voltage is 500 V a.c. The MTU measures 124 mm wide, 186.5 mm high (including latch), and 47 mm deep, weighing 0.45 kg. Its 36 mechanical key combinations ensure correct module pairing, while the rotary switch simplifies address configuration.

Industry Applications

In oil and gas refineries, the TU849 supports redundant Optical ModuleBus modems for critical control loops, ensuring that a single modem failure does not interrupt communication to the distributed control system. For power generation plants, this termination unit provides a reliable interface between non-redundant I/O and redundant modems, reducing the risk of data loss during routine maintenance. The unit's dual power supply connections allow each modem to be powered independently, enhancing system availability in continuous process environments. By using the TU849, engineers can achieve high uptime without the complexity of fully redundant I/O architectures.

Installation & Setup Guidance

Mount the TU849 vertically or horizontally on a standard DIN rail. Use a screwdriver to lock or unlock the mechanical latch that secures the unit to the rail. Set the cluster address (1 to 7) via the rotary switch before connecting cables. Configure the mechanical keys for each modem position using a screwdriver—each key has six positions, enabling 36 combinations to prevent wrong module insertion. Connect the single electrical ModuleBus cable to the designated terminal, and wire each modem's power supply to the dual input terminals. Ensure wire stripping length and torque (0.5 Nm) comply with specifications. The unit is IP20 rated, so install it in a clean, dry enclosure.

Maintenance & Reliability

The TU849 is a passive MTU with no active components, requiring minimal routine care. Periodically inspect the DIN rail latch and mechanical keys for wear or damage. Verify that the rotary switch remains in the correct position and that all terminal screws are tight. The unit operates reliably from 0 to +55 °C (approvals issued for +5 to +55 °C) and can be stored from -40 to +70 °C. For vertical mounting, the maximum ambient temperature is 40 °C. With CE marking, cULus Hazardous Location (Class 1 Zone 2, ATEX Zone 2), and marine certifications (ABS, BV, DNV-GL, LR), the TU849 is built for demanding industrial environments. Regular visual checks and adherence to environmental limits ensure long service life.

Compatibility & Integration

The TU849 is designed specifically for use with ABB TB840 and TB840A Optical ModuleBus Modems. It connects to a single electrical ModuleBus and supports line redundancy. The unit is not a master or slave—it serves as a passive interface. For redundant I/O configurations, use the TU848 termination unit instead. The TU849 integrates seamlessly into ABB's 800xA and similar distributed control systems that employ ModuleBus communication. Before ordering, verify that your system requires non-redundant I/O with redundant modems. BluePLC Industrial can assist with compatibility checks and provide the TU849 for your next project.

Selection Guide & Purchasing Advice

When selecting the TU849, confirm that your application requires a single I/O connection with dual power supply for two TB840/TB840A modems. Ensure your DIN rail is standard profile and that the ambient temperature does not exceed 55 °C (or 40 °C for vertical mounting). The unit weighs 0.45 kg and measures 124 x 186.5 x 47 mm, so plan cabinet space accordingly. BluePLC Industrial stocks the ABB TU849 (3BSE042560R1) and can provide current lifecycle status and availability. Contact our team for pricing, lead times, and to discuss replacement options if your existing system uses older termination units.