Configured for intrinsically safe I/O termination and field wiring routing in hazardous area applications, the Allen-Bradley 1797-TB3 (1797-TB3 Terminal Base Unit) provides direct physical/electrical execution. The hardware establishes a localized interface between field transmitters, actuators, and the active backplane architecture, managing voltage routing across multiple termination paths without compromising spark-containment design criteria.

Terminal Topology & Circuit Mapping

The layout features a multi-tier physical design containing three termination strips that optimize routing density within small enclosure spaces. Terminal paths are physically segregated to separate active I/O loop connections from shared common returns.

• Top Row: Dedicated to field I/O active signal conductors.

• Middle Row: Assigned to common return terminations.

• Physical Layout: Two distinct terminal rows containing 1 row with 16 terminals and 1 row with 18 terminals, culminating in 52 total hardware connection points.

Hardware Specifications

Deterministic Network Architecture & Backplane Bus Velocity

The terminal base assembly utilizes a passive electronic midplane that routes data links and module power directly through adjacent bases. This bus configuration supports distributed topologies across Profinet / EtherNet/IP deterministic networks via adapter gateways. The internal structure does not restrict backplane bus communication velocity licenses, maintaining native data throughput while enforcing galvanic boundaries. Changes in I/O density scaling are accommodated via the modular snap-fit interlocking design, ensuring that firmware flash compatibility is maintained across all attached active electronic modules.

Ordering Information

• 1 x 1797-TB3 FlexEx Terminal Base Unit

• 2 x Interlocking bus connector covers

Field Installation Guidelines

Mounting and Mechanical Alignment

• Snap the terminal base directly onto standard DIN-rail assemblies, ensuring the side-locking bus connectors latch firmly with the preceding unit.

• Tighten all terminal wire clamping screws to a torque specification between 0.56 and 0.79 Nm to maintain electrical contact stability.

Conductor Routing and Shielding Rules

• Keep all intrinsically safe field wiring separated from non-intrinsically safe power infrastructure within the cabinet enclosure.

• Ground the instrument cable shields at the designated enclosure bulkhead grounding busbar rather than at the terminal base frame.

Frequently Asked Questions

• What is the hot-swap capability limitation regarding active electronic modules mounted to this unit?

  The terminal base permits removal and insertion of compatible modules under field power, provided the area is verified non-hazardous or the module meets specific intrinsic safety standards.

• How does the backplane power distribution operate across adjacent terminal assemblies?

  Power and communication links pass horizontally through the integrated side connectors, forming a continuous internal system bus across the assembled array without external jumpers.

• What type of conductor insulation and gauge is compatible with the integrated screw clamps?

  The screw clamp mechanisms accommodate solid or stranded copper wire rated for industrial signaling, stripped to the manufacturer standard depth specified in the manual.

• Is there any channel-to-channel electrical isolation built into this passive terminal base?

  No, this unit provides point-to-point pass-through wiring, and any structural channel isolation is determined solely by the active I/O module snapped onto the base.

• What occurs if the terminal screw torque falls outside the 0.56 to 0.79 Nm specification?

  Under-torquing leads to increased contact resistance and potential open circuits, while over-torquing risks stripping the internal threads and damaging the contact plates.

• Can this terminal base be deployed directly inside Class I Division 1 environments without an enclosure?

  The hardware must be mounted inside an approved, dust-tight and moisture-protected industrial enclosure that complies with local zone regulations for hazardous areas.

• What is the continuous isolation voltage rating between the field wiring terminals and the backplane?

  The physical layout and component separation provide a continuous isolation performance ceiling verified up to 125 V between the active processing logic and field loops.

• Does this base unit contain active components that require configuration during software commissioning?

  No, the terminal base is a purely passive mechanical and electrical routing interface that requires no software configuration, node addresses, or firmware flashes.