Allen-Bradley 1756-OH8I – ControlLogix Isolated Output Module with 8-Point Individually Isolated Outputs

The Allen-Bradley 1756-OH8I is a ControlLogix isolated output module. Specifically, this module provides 8 individually isolated outputs. It operates at 120 Volts DC with sink-source configuration. Furthermore, the voltage range spans from 90 to 146 Volts DC. Consequently, this module suits high-voltage DC applications requiring complete channel-to-channel isolation.

Ordering Configuration and Product Identification

• Manufacturer: Rockwell Automation.

• Brand: Allen-Bradley.

• Part Number: 1756-OH8I.

• Series: ControlLogix.

• Module Type: Isolated Output Module.

• Number of Outputs: 8-point individually isolated.

• Voltage Rating: 120 Volts DC (sink-source).

• Operating Voltage Range: 90-146 Volts DC.

• Enclosure: None (open-style module).

• UPC: 10612598171443.

• Temperature Code (North America): T4A factory designated.

• Therefore, the Allen-Bradley 1756-OH8I offers complete channel isolation for critical DC applications.

Output Current Ratings

• Maximum Current per Point (at 60°C): 2 Amps.

• Maximum Current per Module (at 60°C): 8 Amps total.

• Minimum Current Load per Point: 2 milliamps.

• Surge Current per Point: 4 Amps maximum.

• Voltage Drop (ON-state at 2A): 2 Volts DC.

• OFF-state Leakage Current: 1 milliamps per point.

• Output Type: Sinking or sourcing (configurable).

• Signal Delay (ON to OFF): 2 milliseconds maximum.

• Signal Delay (OFF to ON): 2 milliseconds maximum.

• High Performance: Suitable for demanding DC switching applications.

• Thus, the 1756-OH8I provides robust output capacity with fast switching response.

Power Dissipation and Backplane Current

• Power Dissipation (Max at 60°C): 3.3 Watts.

• Thermal Dissipation: 11.25 BTU per hour (3.3W).

• Backplane Current (5.1 Volts): 210 milliamps.

• Backplane Current (24 Volts): 2 milliamps.

• Overall Backplane Power: 1.1 Watts.

• Isolation Voltage (Continuous): 250 Volts (output-to-backplane and output-to-output).

• Isolation Type Test: 1350 Volts AC for 2 seconds (basic insulation).

• Enclosure Type: Open-style (requires chassis installation).

• Consequently, the Allen-Bradley 1756-OH8I consumes minimal backplane power while providing high isolation.

Individually Isolated Outputs

• Isolation Type: Output-to-backplane isolation.

• Isolation Type: Output-to-output isolation.

• Isolation Rating: 250 Volts continuous.

• Test Voltage: 1350 Volts AC for 2 seconds.

• Insulation Type: Basic insulation rating.

• Benefit: No common ground required between channels.

• Application: Mixed voltage devices on same module.

• Noise Immunity: Excellent rejection of channel-to-channel interference.

• Safety: Prevents fault propagation between outputs.

• Flexibility: Each output can switch different DC voltages within range.

• Therefore, the 1756-OH8I eliminates ground loop issues in complex systems.

Removable Terminal Blocks

• Compatible Terminal Block 1: 1756-TBCH.

• Compatible Terminal Block 2: 1756-TBS6H.

• Terminal Block Type: Removable (plug-in design).

• Wiring Benefit: Easy module replacement without rewiring.

• Installation Speed: Faster than fixed terminal blocks.

• Field Wiring: Accepts standard copper conductors.

• Maintenance: Simple disconnect and reconnect.

• Screw Torque: Follow standard ControlLogix specifications.

• Thus, the 1756-OH8I simplifies installation and reduces downtime.

Temperature and Environmental Ratings

• Operating Temperature Range: 0°C to 60°C (32°F to 140°F).

• Relative Humidity: 5% to 95% non-condensing.

• Operational Vibration: 2G at 10 to 500 Hz.

• Operational Shock: 20G maximum rating.

• Temperature Code: T4A (North America factory designation).

• Environmental Tolerance: Designed for industrial control panels.

• Chemical Resistance: Avoid direct chemical exposure.

• Storage Temperature: Standard ControlLogix specifications.

• Moreover, the Allen-Bradley 1756-OH8I withstands typical industrial environments reliably.

Installation Guide

First, verify that all system power sources are completely disconnected. Then, select an available slot in your ControlLogix chassis. The 1756-OH8I can be placed in any I/O slot. After that, slide the module into the chosen slot. Push firmly until the backplane connector is fully seated. Next, select your removable terminal block (1756-TBCH or 1756-TBS6H). Attach the terminal block to the module front. Then, wire your field devices to the terminal block terminals. Connect the external DC power supply (90-146V DC) to each isolated output as required. Each output has its own isolated common. Therefore, different voltages can be used on different channels. Then, apply backplane power by turning on the ControlLogix system. Download your output configuration to the module. Finally, test each output point using your control program. Verify the 2ms signal delay meets your application requirements. As a result, the Allen-Bradley 1756-OH8I will provide reliable isolated DC output control.

Packaging List

• One Allen-Bradley 1756-OH8I isolated output module

• One removable terminal block (1756-TBCH or 1756-TBS6H, order separately)

• One product identification label

• One installation and wiring guide

• One output configuration sheet

Common FAQs

Q1: How many outputs does the Allen-Bradley 1756-OH8I provide?
A: This module provides 8 individually isolated outputs. Therefore, each channel has its own isolated common. Consequently, different voltages can be used on different channels.

Q2: What is the maximum current per point on the 1756-OH8I?
A: At 60°C, the maximum current is 2 Amps per point. The module total is 8 Amps at 60°C. Surge current capacity is 4 Amps per point. Therefore, proper derating is required for high temperatures.

Q3: What voltage range does the Allen-Bradley 1756-OH8I support?
A: The operating voltage range is 90-146 Volts DC. The rated voltage is 120 Volts DC. Therefore, it suits standard 110-125V DC industrial control systems.

Q4: What is the isolation rating of the 1756-OH8I?
A: Output-to-backplane isolation is 250 Volts continuous. Output-to-output isolation is also 250 Volts continuous. Type testing is performed at 1350 Volts AC for 2 seconds. Therefore, channels are fully isolated from each other.

Q5: What is the signal delay time for the Allen-Bradley 1756-OH8I?
A: The maximum output signal delay is 2 milliseconds for both ON to OFF and OFF to ON transitions. Consequently, this module suits applications requiring fast DC output switching. Always verify timing meets your specific requirements.