1746-OW8 Digital Contact Output Module Allen-Bradley

Product Overview

The Allen-Bradley 1746-OW8 is an 8-channel electromechanical relay contact output module engineered for the SLC 500 programmable controller architecture. Operating across wide AC and DC voltage spans (5–265 Vac / 5–125 Vdc), this module provides dry-contact switching capabilities across two isolated groups of four Normally Open (N.O.) channels. The 1746-OW8 enables direct control of interposing circuits, motor starters, solenoid valves, and warning beacons without requiring auxiliary interposing relays.

Compatible with modular SLC 5/01 through SLC 5/05 processors and remote 1746 I/O chassis adapters, the module draws 85 mA at 5 Vdc and 90 mA at 24 Vdc from the backplane. Its dual-group isolated common architecture allows engineers to switch distinct AC and DC supply voltages within a single single-slot chassis location, conserving enclosure footprint and simplifying panel assembly.

Key Features and Benefits

• Dual Isolated Common Groups: Features 2 isolated groups (4 channels per group) allowing multi-voltage AC and DC circuit control.
• Wide Operational Voltage Span: Switches field loads ranging from 5 to 265 Vac (47–63 Hz) and 5 to 125 Vdc safely.
• Eliminates Interposing Relays: High-capacity dry contacts drive heavy field coils directly, reducing wiring complexity and enclosure costs.
• Hazardous Location Certification: Certified for Class 1, Division 2 hazardous operating environments (Pollution Degree 2 compliant).
• Low Backplane Power Draw: Consumes only 85 mA at 5 Vdc and 90 mA at 24 Vdc with a low maximum heat dissipation of 3.7 W.
• Robust Mechanical Durability: Rated for 30g operational shock and 2g vibration resistance across a -25 °C to +60 °C temperature window.

Technical Specifications

Detailed electrical, mechanical, and operational parameters for the Allen-Bradley 1746-OW8 are structured below:

Target Equipment and Application Scenarios

• Direct control of 120/240 Vac motor starter contactors and heavy industrial solenoid coils.
• Mixed-voltage control panels requiring simultaneous switching of 24 Vdc pilot circuits and 120 Vac alarm horns.
• Remote I/O rack expansion slots running over RIO communication networks in water/wastewater plants.
• Retrofit modernization of legacy SLC 5/01 through SLC 5/05 PLC racks in chemical and material handling facilities.

Diagnostic Capabilities and Signal Analysis

The Allen-Bradley 1746-OW8 provides clear hardware-level status visualization via individual front-panel LED indicators. Each LED illuminates when the internal logic energizes the corresponding contact coil. Because mechanical relays can experience contact wear under highly inductive loads, verifying LED illuminations against field-side voltage measurements assists maintenance teams in diagnosing contact pitting or welded relay states without taking the PLC chassis offline.

Global PLC Spare HUB's Insight & Field Experience

While the 1746-OW8 eliminates external interposing relays for many applications, driving highly inductive AC or DC loads (such as large solenoid valves or brake coils) subjects mechanical contacts to voltage spikes during turn-off. We strongly advise installing external surge suppressors—such as RC networks for AC circuits or flyback diodes for DC circuits—directly across field loads to extend internal relay contact lifespans.

When wiring the two common groups, keep total group current under 8.0 A continuous. In Class 1, Division 2 hazardous locations, never pull or plug the module, terminal block, or field connections while the backplane or field circuits remain energized to prevent hazardous electrical arcing.

Compliance, Shipping, and Warranty Terms

• Package Contents: 1 x New factory-sealed Allen-Bradley 1746-OW8 8-channel relay output module in original factory protective box.
• Warranty Coverage: Fully backed by a 12-month factory replacement warranty active from the dispatch date.
• Express Global Courier: Fast international dispatch within 24–48 hours using express DHL, FedEx, and UPS courier networks.

Frequently Asked Questions (FAQ)

Question: Can I wire 120 Vac loads on Group 0 and 24 Vdc loads on Group 1 simultaneously?

Answer: Yes, the two 4-point output groups are electrically isolated from each other, allowing separate supply voltages across each common terminal.

Question: Does this relay output module require external power connections to drive the internal relay coils?

Answer: No, the internal relay coils derive control power directly from the SLC backplane (85 mA at 5 Vdc and 90 mA at 24 Vdc).

Question: What protective measure prevents premature contact failure when switching inductive solenoid valves?

Answer: Installing external metal oxide varistors (MOVs) or RC suppression networks across AC field loads suppresses voltage transients during contact break.

Question: Is this relay unit compatible with SLC 500 remote expansion racks?

Answer: Yes, it installs into any available slot of a remote 1746 chassis, provided Slot 0 contains a 1746 communication adapter.

Question: What safety precaution must be observed when working on this unit in hazardous environments?

Answer: Power down both backplane supply and field circuit power prior to disconnecting terminal blocks or replacing the hardware to prevent electrical arc ignition risks.

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