TU531 is the screw-terminal terminal unit for compatible ABB AC-voltage and relay I/O modules. It forms the retained field-wiring layer beneath the plug-in electronics and is the direct terminal-technology counterpart to the spring-terminal TU532.

The base offers forty terminal positions and up to thirty-two channels in four groups. The installed I/O module assigns the individual channel functions, so the module type and its wiring diagram remain essential to terminal-unit selection.

• Provides the screw-clamp field connection beneath a compatible AC or relay I/O module.
• Retains terminal wiring when the plug-in module is removed for inspection or approved service.
• Organizes the module-defined signals into four groups for labeling and troubleshooting.
• Transfers the applicable field-voltage and current paths through the internal connector to the inserted electronics.
• Supports grounded DIN-rail or wall-mounted AC500 station construction.

• Use the I/O module wiring diagram to confirm every terminal assignment and electrical limit.
• Choose TU531 when screw terminals are required; TU532 is the spring-terminal alternative.
• Do not substitute a TU541 or TU542 high-current 24 V DC base for this AC and relay terminal class.
• Select a specifically identified hot-swap variant when online module exchange is part of the maintenance plan.
• Match standard and XC environmental variants to the actual station conditions.

• AC500 and S500 remote I/O stations using compatible AC-input, AC-output or relay modules.
• Industrial panels standardized on screw-clamp conductor termination.
• Service replacements that must preserve the existing field wiring and terminal numbering.
• Machine-control cabinets where module electronics and field terminations are maintained as separate assemblies.