ABB TU840 3BSE020846R1 Module Termination Unit

The ABB TU840 3BSE020846R1, also cataloged as the TU840 Module Termination Unit, operates as a dedicated hardware component for housing dual TB840/TB840A Optical ModuleBus Modems in redundant configurations within ABB S800 I/O systems. Mounted directly on standard DIN rails, the passive unit routes redundant power supply connections and dual electrical ModuleBus communication lines to downstream S800 I/O clusters. An integrated rotary address switch allows manual assignation of cluster addresses from 1 to 7, while keying mechanisms prevent incorrect modem placement during system setup.

Suffix Breakdown & Model Matrix

Hardware Specifications

Backplane Bus Communication Velocity and Redundancy

The TU840 supports high-speed dual electrical ModuleBus routing between the hot-swappable TB840/TB840A modems and attached S800 I/O modules. Integrated bus lines maintain signal integrity across long backplane chains while preventing data latency during modem failover. Dual keying slots at each modem position (4 keys total) enforce mechanical keying lockouts using 36 unique position combinations, verifying physical modem hardware alignment before power distribution takes effect.

Frequently Asked Questions

Q: How does the TU840 handle cluster address assignment for attached optical modems?

A: The unit features an onboard rotary address switch on its front casing. Adjusting the switch to a position between 1 and 7 sets the cluster address directly on the hardware backplane, routing ModuleBus communication frames to the specified node.

Q: Is hot-swapping supported for TB840 or TB840A modems installed on the TU840 MTU?

A: Yes. Because the TU840 distributes power and dual electrical ModuleBus signals via isolated internal backplane traces, a failed or offline TB840/TB840A modem can be extracted and replaced while the alternate redundant modem remains active.

Q: What are the thermal restrictions based on physical mounting orientation?

A: When mounted horizontally on a DIN rail, the TU840 supports operating temperatures up to +55 deg C. When mounted vertically, ambient operating temperatures must not exceed +40 deg C to allow sufficient passive convective cooling.

Field Installation Guidelines

1. DIN Rail Mounting: Align the rear latch mechanism of the TU840 with a standard 35 mm DIN rail. Press firmly until the mechanical locking clip seats properly to maintain earth ground continuity.
2. Set Cluster Address: Rotate the integrated cluster address selector switch using a small flathead screwdriver to assign the designated cluster position (1 to 7) prior to applying 24 VDC power.
3. Configure Mechanical Keying: Adjust the four mechanical keying dials (two per modem slot) to match the keying profile of the TB840 or TB840A optical modem modules.
4. Power and ModuleBus Wiring: Wire incoming 24 VDC supply lines to the primary power input terminals using wire sizes within standard S800 terminal specifications. Confirm field connections meet the maximum 50 V insulation threshold.
5. Modem Insertion: Insert the primary and secondary TB840/TB840A modems firmly into their respective slots on the MTU until top retaining clips lock securely into position.