ABB TU840 Termination Unit for Redundant I/O Systems

Product Introduction

When building redundant I/O architectures, the ABB TU840 termination unit (part number 3BSE020846R1) provides a reliable foundation. This Module Termination Unit (MTU) is designed for redundant configuration of Optical ModuleBus Modem TB840/TB840A modules. It is a passive unit that connects power supply, double electrical ModuleBus, and two TB840/TB840A modules. A rotary switch sets the cluster address from 1 to 7, and four mechanical keys (two per position) prevent insertion of wrong module types. Each key has six positions, offering 36 different configurations that can be changed with a screwdriver. The TU840 supports redundant I/O, while the TU841 is used for non-redundant I/O.

Technical Specifications Breakdown

The TU840 operates on a 24 V DC power input (19.2–30 V) and distributes ModuleBus current at maximum 5 V 1.5 A and 24 V 1.5 A. Its rated insulation voltage is 50 V, with a dielectric test voltage of 500 V AC. Power dissipation is only 2.0 W, making it energy-efficient. Acceptable wire sizes include solid 0.2–2.5 mm² and stranded 0.2–2.5 mm² (24–12 AWG), with a recommended torque of 0.5 Nm. The unit mounts vertically or horizontally on a DIN rail and has an IP20 ingress protection rating according to IEC 60529. Operating temperature ranges from 0 to +55 °C (approvals issued for +5 to +55 °C), and storage temperature from -40 to +70 °C. Relative humidity tolerance is 5 to 95% non-condensing.

Industry Applications

The TU840 is ideal for process control systems requiring high availability, such as oil and gas, power generation, and chemical plants. Its redundant ModuleBus and module redundancy ensure continuous operation even if one TB840/TB840A fails. The mechanical keying feature reduces installation errors, saving time during commissioning. In a typical redundant I/O setup, the TU840 connects to an ABB controller via ModuleBus, providing a secure and organized termination point for field wiring. The double ModuleBus connection allows seamless integration with redundant communication paths, minimizing downtime.

Installation & Setup Guidance

Mount the TU840 on a standard DIN rail using the integrated latching device for locking and grounding. Ensure the power supply is within 19.2–30 V DC. Set the cluster address using the rotary switch (positions 1–7). Configure the mechanical keys according to the module type using a screwdriver. Use wire sizes within the specified range (solid 0.2–2.5 mm² or stranded 24–12 AWG) and tighten terminals to 0.5 Nm. The unit can be mounted vertically or horizontally, but note that maximum ambient temperature is 55 °C for horizontal and 40 °C for vertical mounting. No special tools are required beyond a standard screwdriver.

Compatibility & Integration

The TU840 communicates via the ModuleBus protocol and is compatible with TB840/TB840A Optical ModuleBus Modems. It supports line redundancy and module redundancy, making it suitable for redundant I/O systems. The unit is passive and does not act as a master or slave. It integrates with ABB control systems that use ModuleBus for I/O communication. The double ModuleBus connection allows connection to two separate bus cables for enhanced reliability. For non-redundant applications, use the TU841 instead.

Selection Guide & Purchasing Advice

Before purchasing, verify that your system requires redundant I/O and that you have TB840/TB840A modules. The TU840 includes mechanical keying, so ensure the keys are set correctly for your module type. Check that your power supply provides 24 V DC within the specified range. The unit weighs 0.45 kg and measures 124 mm wide, 186 mm high (including latch), and 47 mm deep. BluePLC Industrial offers the ABB TU840 with fast shipping and expert support. Please verify current lifecycle status and availability with BluePLC Industrial before ordering.