Product Overview
The Allen-Bradley 1756-OB8EI is a ControlLogix discrete output module engineered for demanding industrial control environments. It provides eight (8) electronically fused, individually isolated sourcing output channels, delivering a nominal 24V DC output with an operating range of 10-30V DC. This module is designed to energize loads such as relay coils, pilot lamps, buzzers, horns, sirens, and valves, making it a versatile component in automation systems.
With its robust construction and precise current control, the 1756-OB8EI ensures reliable switching performance while protecting downstream equipment from overcurrent conditions. Its compact single-slot design fits directly into any 1756 ControlLogix chassis, supporting both local and distributed I/O configurations.
Technical Specifications
The following table outlines the key technical parameters of the Allen-Bradley 1756-OB8EI module:
| Parameter |
Value |
| Manufacturer |
Rockwell Automation |
| Series |
ControlLogix |
| Part Number |
1756-OB8EI |
| Module Type |
Digital DC Sourcing Output |
| Number of Outputs |
8 (Electronically fused, individually isolated) |
| Output Voltage |
24V DC |
| Output Voltage Range |
10-30V DC |
| Output Current per Channel |
2 A @ 60 °C (140 °F) |
| Output Current per Module (Max) |
10 A @ 60 °C (140 °F); 16 A @ 55 °C (131 °F) linear derating |
| Backplane Current (5.1V DC) |
250 mA |
| Backplane Current (24V DC) |
2 mA |
| Power Dissipation |
4.7 W @ 60 °C (140 °F) |
| Output Signal Delay (OFF to ON) |
1 ms, max |
| Output Signal Delay (ON to OFF) |
5 ms, max |
| Enclosure Type Rating |
None (open-style) |
| Removable Terminal Block |
1756-TBCH; 1756-TBS6H |
Real-World Applications
The Allen-Bradley 1756-OB8EI excels in applications requiring high-density, fused, isolated discrete outputs. Typical use cases include:
-
Machine Control: Energizing solenoid valves, contactors, and indicator lamps in automated assembly lines.
-
Process Control: Driving alarm annunciators, horns, and motor starters in continuous processing plants.
-
Material Handling: Controlling conveyor diverters, gate actuators, and sortation equipment.
Because each output is electronically fused and individually isolated, the 1756-OB8EI minimizes downtime by preventing a single fault from disabling multiple points—a critical advantage for high-availability systems.
Installation & Setup
Installing the 1756-OB8EI is straightforward:
- Power down the chassis and insert the module into an available slot, ensuring proper seating.
- Connect the removable terminal block (RTB) using the compatible 1756-TBCH or 1756-TBS6H.
- Wire field devices to the appropriate output terminals, observing polarity and voltage ratings (10-30V DC).
- Configure the module in the ControlLogix programming software, setting fault and program mode behavior as needed.
Note that the module is open-style; install it in a suitable enclosure to meet environmental requirements.
Maintenance & Reliability
Routine maintenance for the 1756-OB8EI is minimal. Periodically inspect wiring connections and verify that the ambient temperature stays within the 0-60 °C operating range. The module's electronic fusing eliminates the need to replace physical fuses, reducing spare parts inventory and service time.
Its isolation voltage of 50V continuous and routine testing at 1350V for 2 seconds ensure robust protection against transient events, contributing to long service life.
Compatibility & Integration
The 1756-OB8EI integrates seamlessly into any ControlLogix system. It occupies a single slot and supports multiple instances on local or distributed I/O racks. The module is compatible with any POINT I/O communication adapter for implementing distributed I/O architectures, allowing flexible system scaling.
Selection Guide & Purchasing Advice
Before purchasing, verify that your system has an available ControlLogix slot and that the backplane current capacity (250 mA @ 5.1V, 2 mA @ 24V) is within your power supply limits. Ensure you have the correct RTB (1756-TBCH or 1756-TBS6H) for wiring.
When sourcing genuine Allen-Bradley components, trust PLC Source PRO for authentic parts and reliable service. Our inventory is sourced directly from authorized channels, ensuring quality and compatibility.