Allen-Bradley 1746-OW8/A Relay Output Module

The Allen-Bradley 1746-OW8/A, also cataloged as the 1746-OW8 digital output module, operates as a relay contact output interface for discrete load switching within the SLC 500 backplane system. It provides direct electromechanical execution of ON/OFF control signals from the processor to field AC/DC circuits via isolated relay contacts.

Hardware Specifications

Backplane Bus Execution & Relay Contact Switching (Allen-Bradley SLC 500 Architecture)

The module interfaces with the SLC 500 chassis backplane via cyclic data exchange. Output state updates are synchronized through backplane scan cycles, with deterministic update behavior dependent on controller scan time.

Relay outputs provide galvanically separated switching paths using mechanical contact structures. Channel grouping is arranged in 4-point commons, defining shared return paths for output load circuits. Contact closure and release are governed by internal coil energization driven from backplane logic states.

Optical isolation between logic section and output driver stage limits electrical coupling between backplane and field terminals. Relay actuation introduces mechanical switching delay relative to solid-state output modules.

Frequently Asked Questions (FAQ)

Q: What is the backplane current requirement of 1746-OW8/A?
A: The module draws low backplane logic current for relay coil control; field load current is not sourced from the backplane.

Q: Can outputs be hot-swapped under load conditions?
A: Hot-swap is not supported while relay contacts are actively switching under load; removal requires de-energized output conditions.

Q: How does point grouping affect load wiring?
A: The module uses 4-point commons; each group shares a common return path, affecting external circuit segmentation.

Field Installation Guidelines

The module must be inserted into a powered-down SLC 500 chassis to avoid backplane signal disturbance. Ensure terminal wiring follows group common allocation (4 points per common). Maintain separation between AC and DC field wiring to prevent cross-coupling on relay contacts.

Shield termination should follow standard control cabinet grounding practice, with single-point earth reference at the chassis ground bar. Relay contact circuits must observe maximum load current limits per point to avoid contact degradation.