ABB TU842 3BSE020850R1 Redundant I/O MTU

The ABB TU842, also cataloged as the TU842 Redundant I/O MTU, operates as a dedicated hardware component for field signal termination and ModuleBus distribution within the ABB Ability System 800xA I/O system.

Hardware Specifications

ModuleBus Distribution and I/O Channel Configuration

The ABB TU842 provides electrical termination and signal routing between System 800xA I/O modules and field wiring. The MTU distributes two ModuleBus connections to installed I/O modules and the following MTU position in the bus chain. The outgoing position signal is shifted internally to generate the correct addressing for subsequent I/O modules.

The unit supports up to 16 field signal channels with two I/O connections and one ZP connection per channel. Mechanical keying is implemented through four configurable keys, providing 36 possible configurations to prevent incorrect I/O module insertion.

Frequently Asked Questions

Q: What type of mounting interface is used for the TU842?
A: The TU842 is installed on a standard DIN rail and uses a mechanical latch mechanism for physical locking and grounding connection.

Q: Does the mechanical keying change the electrical function of the MTU?
A: No. The mechanical keys provide module identification and insertion control only. They do not modify the electrical operation of the MTU or connected I/O module.

Q: What wire sizes are supported for terminal connections?
A: The TU842 supports solid wire sizes from 0.2 to 4 mm2 and stranded wire sizes from 0.2 to 2.5 mm2 (24 to 12 AWG). The recommended terminal torque is 0.5 to 0.6 Nm.

Field Installation Guidelines

Install the TU842 on a horizontal standard DIN rail position with sufficient mechanical clearance for terminal access and locking device operation.

Connect field wiring according to the terminal assignment of the selected ABB System 800xA I/O module configuration. Maintain separation between signal wiring, process power wiring, and external interference sources according to site electrical installation practices.

Verify that the DIN rail mounting latch provides proper mechanical retention and grounding continuity. The terminal block connections should be tightened within the specified torque range to maintain electrical contact integrity.

For redundant I/O configurations, confirm that the installed I/O modules match the configured mechanical key positions before insertion. Verify ModuleBus connections between adjacent MTUs and I/O modules before system power application.