1794-OA8I Allen Bradley Flex I/O 8 Channel Isolated AC Module

1794-OA8I Solid-State AC Output Architecture

The 1794-OA8I is an 8-channel solid-state isolated AC digital output module in the Allen-Bradley Flex I/O Series manufactured by Rockwell Automation. Designed for switching 120V AC field loads, this module provides channel-to-channel and channel-to-backplane galvanic isolation rated at 120V continuous (1250V AC dielectric withstand for 60 seconds). It supports up to 500 mA output current per channel, yielding a total module capacity of 4.0 A. Operating across an ambient temperature envelope of -20 to 55 °C, the module interface snaps onto compatible terminal bases including 1794-TB2, 1794-TB3, 1794-TB3S, 1794-TBN, and 1794-TBNF, requiring Keyswitch Position 8. Power dissipation ranges from 4.1W at 0.5A up to 6.3W at 1.0A maximum load, with 80 mA backplane current draw at 5V DC via the Flexbus network.

Technical Specifications Summary

Target Equipment & Field Integration Scenarios

The solid-state design and individual channel isolation of the 1794-OA8I suit high-duty AC switching applications across diverse industrial control enclosures:

• 120V AC solenoid valve actuation in pneumatic transport and water treatment systems
• Interfacing with magnetic contactor coils and motor starters without interposing relays
• Drive run/stop and direction control signals operating on distinct AC power feeds
• Machine visual alarm columns, horns, and stack light indicators requiring fast cycle rates
• Process control loops demanding isolated field wiring to isolate phase-to-phase AC circuits

Diagnostic Features & Electrical Protection

Real-time visual feedback and electrical isolation maintain operational uptime and assist troubleshooting:

• Status LED Array: Eight yellow field-side status LEDs illuminate when the corresponding output circuit receives active gate trigger signals.
• Channel-to-Channel Isolation: Individual channel commons prevent cross-phase short circuits when switching loads fed from different AC transformers or phase legs.
• Solid-State Switching: Triac-based solid-state outputs eliminate contact bounce and mechanical contact wear during high-frequency pulse operations.

Packaging, Fast Delivery & Guarantee

• Product Condition: 100% Original, Factory Sealed Stock
• Warranty Terms: Full 12 Months Replacement Warranty
• Dispatch Window: Same-day or next-business-day processing
• Global Freight Options: Express air shipping via FedEx, UPS, or DHL

Global PLC Spare HUB's Insight

The 1794-OA8I is an ideal solid-state alternative to relay output modules when rapid switching speeds or high duty cycles would prematurely wear out mechanical contacts. However, engineers must account for two triac characteristics during design: off-state leakage current and minimum on-state holding current. The 2.25 mA maximum leakage current can keep low-power loads—such as high-impedance digital inputs or high-efficiency LED indicators—partially energized when the channel is OFF. Conversely, field loads drawing under 5 mA will fail to latch the triac ON. Installing a parallel load resistor (bleeder resistor) across sensitive low-power field devices stabilizes both states and prevents ghost-voltage trips.

Frequently Asked Questions (FAQ)

Q: Why does a field load connected to the module stay energized or flicker when the channel status LED is turned OFF?

A: Triac solid-state switches exhibit up to 2.25 mA off-state leakage current; on low-power loads like high-efficiency relays or LED indicators, this small leakage current is sufficient to maintain excitation, requiring an parallel AC load resistor to bleed off the residual voltage.

Q: How does wiring the terminal base differ for channel-isolated AC modules compared to non-isolated variants?

A: Each isolated channel requires its own 120V AC hot leg connected to the designated odd terminal and its output load connected to the adjacent even terminal, ensuring zero common power bus connections across the 8 channels inside the base.

Q: What branch protection fuse size should be installed on the field power lines for this module?

A: Install 1.6 A, 250V AC slow-blow fuses on field supply lines (or utilize a 1794-TBNF fused terminal base) to protect output circuits from thermal damage caused by load short circuits.

Q: Can this module switch 24V DC loads or low-voltage DC signals?

A: No; triac output switches rely on the zero-crossing nature of alternating current (47…63 Hz) to turn off properly. Applying direct current (DC) will cause the output to lock in an permanently ON state once triggered.

Q: Selection Guide: When should I specify the 1794-OA8I solid-state module instead of the 1794-OW8 electromechanical relay module?

A: Choose the 1794-OA8I for high-frequency switching operations on 120V AC loads where solid-state longevity is needed. Select the 1794-OW8 when switching DC voltages, dry contacts, or loads drawing less than 5 mA on-state current.

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