The Allen-Bradley 1746-OB8 is a high-performance discrete DC output module designed for the SLC 500 programmable logic controller series. This module features eight (8) sourcing outputs, engineered to drive 24V DC to 48V DC loads, including relays, solenoids, and small actuators. As a sourcing module, it switches the positive side of the DC power source to the load, ensuring compatibility with standard industrial control architectures.
Features
Eight (8) sourcing outputs in a single group.
Wide operating voltage range of 10V to 50V DC.
Electro-optical isolation rated at 1500V between I/O terminals and internal control logic.
Integrated status indicators for monitoring output state.
Robust thermal management with specified derating for operation up to 60 degC.
Applications
This module is widely utilized in industrial automation environments for controlling actuators, contactors, and pilot lights within the SLC 500 platform. Its sourcing configuration is ideal for applications requiring positive-side switching in automated manufacturing, material handling, and process control systems.
Technical Specifications
Brand
Allen-Bradley
Product Line
SLC 500
Module Type
Digital DC Output (Sourcing)
Number of Outputs
8 (1 Group of 8)
Voltage Range
10–50V DC
Backplane Current (5V DC)
135 mA
On-Signal Delay
0.1 ms (max resistive load)
Off-Signal Delay
1.0 ms (max resistive load)
Continuous Current per Point
1.0 A @ 30 degC / 0.5 A @ 60 degC
Continuous Current per Module
8.0 A @ 30 degC / 4.0 A @ 60 degC
Maximum Surge Current
3.0 Amps for 10 ms (per point)
Maximum Off-State Leakage
1.0 mA
Total Heat Dissipation
6.9 Watts
Installation Guidelines
Ensure the PLC chassis power is disconnected before inserting or removing the module.
Verify that the module is fully seated in the SLC 500 chassis slot and secured with the top and bottom mounting screws.
Use shielded cabling for I/O connections to minimize electromagnetic interference (EMI) in high-noise environments.
Ensure proper thermal clearance around the module to maintain the specified operating temperature range.
Follow local electrical codes for grounding and wire routing to prevent ground loops and signal degradation.
FAQ
What is the difference between sourcing and sinking outputs?
A sourcing module (like the 1746-OB8) switches the positive voltage (VDC+) to the load, while the load is connected to the common return. A sinking module switches the common return (VDC-) to the load.
Can this module be used at 60 degC?
Yes, the module is rated for operation up to 60 degC, but you must adhere to the thermal derating specifications, which limit the continuous current per point to 0.5 Amps at this temperature.
