1756-OC8 Allen-Bradley ControlLogix 8-Point DC Output Module Stock

Product Overview

The Allen-Bradley / Rockwell Automation 1756-OC8 is an 8-point DC sourcing output module designed for the ControlLogix chassis. Operating within a 30 to 60V DC voltage window, it delivers up to 2 A per point at 60 °C for high-current industrial loads such as heavy-duty solenoids, relays, and contactor coils. Outputs are arranged in two isolated groups of four points each.

Technical Specifications

System Compatibility and Fusing Architecture

The 1756-OC8 connects to process field devices via a 20-pin Removable Terminal Block (RTB). Because internal electronic fusing is not built into the module, external fusing is mandatory to protect transistor circuits from shorted field wiring. Installing a pre-wired Interface Module (IFM) with 5x20mm 4A quick-acting fuses (SOC p/n MQ2-4A) provides dedicated channel protection.

Installation and Mounting Guidelines

Ensure the ControlLogix chassis and system power supply are turned off and properly grounded prior to insertion. Align the module with chassis guides and press firmly until top and bottom latches click into place. Wire field power and loads to the RTB, verifying correct polarity for 48V DC sourcing operation before snapping the RTB housing onto the front faceplate.

Diagnostic Capabilities and Operational Status

The module front panel features an OK status LED along with 8 individual channel LEDs indicating the ON/OFF state of each output point. Through Studio 5000 Logix Designer, engineers can monitor individual point states and configure controller fault responses. Each output channel can be independently programmed to remain OFF, turn ON, or HOLD LAST STATE during controller Program or Fault modes.

Target Equipment and Application Scenarios

• Direct driving of 48V DC high-current solenoid valves in oil and gas manifolds.
• Interfacing with medium-voltage switchgear tripping coils and control relays.
• Actuating DC-powered motor starter coils in power generation facilities.
• Process control loops utilizing 30-60V DC discrete actuator signals.

Global PLC Spare HUB's Insight

During field retrofits, engineers often mistake the 1756-OC8 for standard 24V DC modules like the 1756-OB16E. Applying a 24V DC supply to the 1756-OC8 will lead to unpredictable turn-on behavior because its operating threshold begins at 30V DC. Additionally, always install flyback diodes across external inductive loads (solenoids, brake coils) to suppress back-EMF spikes that could degrade the output transistors over time.

Selection and Purchasing Guide

Select the 1756-OC8 when your field actuators require higher voltage levels (30 to 60V DC) and higher per-point continuous current (up to 2 A) than standard 24V DC modules provide. Choose the 1756-TBNH terminal block for heavy-gauge screw-terminal wiring or the 1756-TBSH spring-clamp terminal block for high-vibration cabinet installations.

Certifications, Package Contents, and 12-Month Warranty

Each unit ships in factory-sealed Allen-Bradley packaging complete with factory inspection documentation. The item is covered by a comprehensive 12-month replacement warranty against manufacturing and functional defects.

Shipping and Express Delivery Terms

Orders are processed immediately and dispatched within 24 to 48 hours following order confirmation. Standard air express shipping is handled via FedEx, UPS, or DHL. Tracking details are emailed automatically upon carrier collection.

Frequently Asked Questions (FAQ)

Q: Why is external fusing strongly recommended for this output module?

A: The module lacks internal electronic fuses, so fast-acting external fuses (such as SOC MQ2-4A 4A fuses on an IFM) are necessary to protect output channels against field wiring short circuits.

Q: Can this module operate reliably on a standard 24V DC power supply?

A: No, the operating voltage range is 30 to 60V DC; a 24V supply falls below the minimum required 30V threshold.

Q: What happens to the outputs if the controller enters Program or Fault mode?

A: Each output channel can be configured individually via software to force ON, force OFF (default setting), or Hold Last State during a fault or mode change.

Q: What is the difference between 1756-TBNH and 1756-TBSH terminal options?

A: The 1756-TBNH uses standard NEMA cage-clamp screw terminals, while the 1756-TBSH utilizes spring-clamp terminals for faster, vibration-resistant wiring.

Q: How do field technicians verify whether an output channel transistor has failed shorted?

A: Disconnect the field load and measure off-state leakage current; a reading significantly higher than 1.0 mA usually indicates a shorted output stage.

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