Allen-Bradley 1756-OA16 ControlLogix 16-Point AC Output Module

Product Overview

The 1756-OA16 is a high-performance discrete AC output module for the Allen-Bradley ControlLogix platform. It features 16 outputs designed to interface with 120/240V AC devices such as motor starters, solenoids, and indicators. The module utilizes TRIAC switching technology, which provides a reliable, solid-state solution for standard industrial AC loads.

The outputs are organized into two isolated groups of eight points each. This architecture allows the module to handle different AC phases or voltage sources within the same module, provided they stay within the 74…265V AC operating range. With built-in mechanical fusing and support for Scheduled Outputs, the 1756-OA16 is a robust choice for time-critical AC control applications.

Technical Configuration

The 1756-OA16 is engineered for safety and precise AC switching:

• Dual-Group Isolation: 16 points are split into two groups of 8, with 250V continuous isolation between groups and from the backplane.

• TRIAC Switching: Employs zero-crossing switching to minimize electrical noise and extend the life of connected AC components.

• Integrated Protection: Each group is mechanically fused with a 3.15 A slow-blow fuse (Littelfuse p/n H2153.15) to protect module circuitry from over-current conditions.

• Broad Voltage Support: While nominally 120/240V, it is specified to operate reliably from 74V to 265V AC at both 50 and 60 Hz frequencies.

• Configurable States: Users can define how each point behaves during a PLC Fault or Program mode (Hold Last State, On, or Off).

Technical Specifications

Technical FAQs

What is the minimum load requirement for the 1756-OA16?

This module requires a minimum load current of 10 mA per point to ensure the TRIAC stays latched. If you are driving a very high-impedance device (like a tiny neon lamp or high-end electronic relay), the output may not turn off correctly or could "flicker" due to leakage current.

What should I do if my TRIAC output latches "On" with a small load?

For loads between 10…50 mA, the module has a lower commutating $dv/dt$ rating ($0.2V/\mu s$). If the TRIAC latches on unexpectedly, you may need to add an external resistor across the output and L2 to increase the total current draw to at least 50 mA, which raises the rating to $4V/\mu s$.

Can I replace the internal fuses?

Yes. The module uses mechanical fuses (Littelfuse p/n H2153.15). However, if a fuse blows, it is critical to investigate the load for a short circuit before replacing it to prevent damage to the RTB or module.

Engineering & Installation Guide

Wiring and Grouping

• Terminal Blocks: Compatible with the 1756-TBNH (NEMA screw) or 1756-TBSH (Spring clamp) 20-pin removable terminal blocks.

• Commoning: Group 0 (Points 0–7) and Group 1 (Points 8–15) have independent L1 and L2 connections. Do not mix DC power with this AC module.

• Pilot Duty: The module is rated for 0.5 A pilot duty, making it suitable for controlling the coils of large motor starters (NEMA size 4 or smaller).

Leakage Current Considerations

The TRIAC outputs have a maximum off-state leakage current of 3 mA. In systems with high-sensitivity inputs or very small loads, this leakage may be enough to keep a device energized. Always verify that your load's "drop-out" current is significantly higher than 3 mA.

Zero-Crossing Switching

The module utilizes zero-crossing synchronization, meaning it waits for the AC sine wave to cross 0V before turning the output on or off. This significantly reduces Inrush Current and Electromagnetic Interference (EMI), which is vital for the longevity of the module and surrounding electronic equipment.