ABB TU891 Compact Terminal Unit

The ABB TU891, also cataloged as the TU891 Compact Terminal Unit, operates as a dedicated hardware component for single I/O module termination and signal distribution within ABB S800 I/O platforms. Configured for single I/O configurations with AI890, AI893, AI895, AO890, AO895, DI890, and DO890 modules, the base provides direct physical/electrical execution. It routes field wiring through 27 gray process terminals, ensuring secure point-to-point connections to active I/O cards without introducing signal latency or line noise.

Hardware Specifications

Deterministic Backplane & I/O Density Scaling Execution

The compact terminal unit incorporates ABB proprietary backplane bus communication velocity Licences and deterministic networking protocols to ensure synchronized data exchange across distributed controller nodes. Operating as a single-channel module base, the hardware manages local field signal frames while supporting high-density I/O configurations. Strict firmware flash compatibility across attached S800 I/O cards maintains low backplane latencies, stable power supply distribution, and high noise immunity with a 500 VAC dielectric test rating.

Frequently Asked Questions

Q: What are the recommended terminal tightening torques for process and power connections on the TU891?

A: The recommended torque for both the 27 process terminals and the power supply connector is 0.5 to 0.6 Nm.

Q: Can the TU891 terminal unit be used in redundant I/O module configurations?

A: No. The TU891 is specifically designed for single I/O module architectures. Redundant configurations require dual-channel termination units.

Q: What wire sizes are supported by the process terminals on the TU891?

A: The process terminals accept solid wire from 0.2 to 4 mm² and stranded wire from 0.2 to 2.5 mm² (24 to 12 AWG).

Field Installation Guidelines

1. Power Isolation & Torque Verification: De-energize all 24 VDC power and field loop circuits before attaching wires. Tighten all screw terminals using a calibrated torque screwdriver set strictly to 0.5 - 0.6 Nm.
2. DIN-Rail Horizontal Mounting: Mount the unit horizontally on standard 35 mm DIN rails. Ensure top and bottom mounting latches fully snap into position to secure mechanical lock and earth grounding contact.
3. Conductor Preparation: Strip process conductors to 7 - 8 mm. Insert solid (0.2 - 4 mm²) or stranded (0.2 - 2.5 mm²) conductors completely into the designated gray process terminals to guarantee 500 VAC dielectric isolation.
4. Grounding & Cable Shielding: Clamp field cable shields to designated chassis ground bars. Ensure ground braids maintain low impedance with at least 5 full thread engagements on M4/M5 cabinet grounding studs.