ABB TU849 Termination Unit for Redundant TB840/TB840A ModuleBus

Product Overview

When maintaining a redundant optical ModuleBus system, the ABB TU849 (3BSE042560R1) termination unit simplifies your setup. This passive MTU connects two TB840/TB840A modems to a single electrical ModuleBus, supporting non-redundant I/O. Designed for reliability, it includes a rotary switch for cluster address setting (1 to 7) and mechanical keying to prevent incorrect module insertion. The unit mounts on a standard DIN rail with a locking latch, ensuring secure grounding and easy service access.

Technical Specifications Breakdown

• Power Input: 24 V d.c. (19.2 – 30 V) – dual power supply connections for each modem ensure continued operation if one supply fails.
• ModuleBus Current Distribution: Maximum 5 V at 1.5 A and 24 V at 1.5 A – sufficient for driving the connected modems and I/O.
• Mechanical Keying: 36 different combinations – six positions per key, two keys per module slot, allow precise configuration to match module types.
• Environmental Ratings: Operating temperature 0 to +55 °C (approvals at +5 to +55 °C), storage -40 to +70 °C, IP20 ingress protection, and Class I equipment (earth protected).
• Certifications: CE marked, electrical safety per EN 61010-1 and UL 61010-1, hazardous location cULus Class 1 Zone 2 and ATEX Zone 2, plus marine certificates (ABS, BV, DNV-GL, LR).

Industry Applications

In a typical redundant Modbus configuration, two TB840 modems connect via the TU849 to a single I/O bus. If one modem fails, the other maintains communication, minimizing downtime. Maintenance engineers appreciate the dual power inputs and mechanical keying, which reduce wiring errors and speed up module swaps.

Installation & Setup Guidance

Mount the TU849 vertically or horizontally on a standard DIN rail. Use a screwdriver to lock the mechanical latch for secure grounding. Set the cluster address (1–7) using the rotary switch before powering up. Connect solid or stranded wires (0.2–2.5 mm², 24–12 AWG) with a recommended torque of 0.5 Nm. Ensure the 24 V d.c. supply is within 19.2–30 V. The mechanical keys can be adjusted with a screwdriver to match the module type – verify the key positions against your TB840/TB840A modules.

Maintenance & Reliability

Routine inspection of the TU849 involves checking the DIN rail latch for secure locking and verifying the dual power supply connections are tight. The passive design means no active components to fail, but environmental factors like humidity (5–95% non-condensing) and temperature (max 55 °C, or 40 °C for vertical mounting) should be monitored. The IP20 rating requires the unit be installed in a clean, dry enclosure. Periodic testing of the redundant modem pair ensures the TU849 continues to provide reliable single ModuleBus connectivity.

Compatibility & Integration

The TU849 is designed for use with ABB TB840 and TB840A Optical ModuleBus Modems. It supports Modulebus communication protocol and line redundancy. The dual power inputs accept standard 24 V d.c. supplies, simplifying integration into existing control panels.

Selection Guide & Purchasing Advice

Before purchasing the ABB TU849, verify your system requires a single ModuleBus connection for redundant TB840/TB840A modems. Confirm the cluster address range (1–7) meets your network topology. The unit does not support hot swap, so plan for planned outages during installation. AutoDCSTech stocks the TU849 (3BSE042560R1) and can advise on compatibility with your existing ABB system. Please verify current lifecycle status and availability with AutoDCSTech before ordering.