Allen-Bradley 1746-OB32 32-Point DC Output Module

Product Introduction

The Allen-Bradley 1746-OB32 is a 32-point sourcing digital DC output module designed for the SLC 500 PLC family. It controls 5 to 50 VDC field devices such as solenoid valves, relay coils, indicator lamps, and interposing relays while maximizing output density within a single chassis slot.

In our field experience, the 1746-OB32 is commonly installed in packaging machines, conveyor systems, and automated assembly lines where cabinet space is limited. One thing to watch out for is that this module is a sourcing transistor output module. Installing it in a system wired for sinking outputs will result in non-functional field devices even though the PLC program appears to operate normally.

Key Technical Specifications

Application Scenarios & The “Trench” Experience

Here’s something that has fooled more than one maintenance crew.

A machine has thirty-two outputs packed into one module. After replacing the PLC card, exactly half of the field devices work while the other half stay dead. The program checks out. Power supplies are healthy.

The problem?

Only one common terminal had been connected. Since the 1746-OB32 divides its outputs into two groups of sixteen, forgetting the second common leaves half the outputs without operating power.

Typical applications include:

• Packaging Industry – Controlling pneumatic manifolds and high-speed diverter gates where large numbers of DC outputs are required.
• Material Handling – Driving conveyor zones, stack lights, and relay interfaces while minimizing rack space.
• Automotive Assembly – Operating valve banks and fixture clamps using multiple 24 VDC outputs.
• Food & Beverage – Controlling filling machines, reject stations, and pneumatic actuators throughout production lines.
• Warehouse Automation – Switching relays and DC actuators across conveyor sorting equipment.

Field Case

A distribution center experienced an unexpected production stop after replacing a failed digital output card during scheduled maintenance. Sixteen outputs responded immediately, while the remaining sixteen never energized.

The replacement module passed every diagnostic test.

After reviewing the wiring, the technician discovered that the second DC common terminal had not been reconnected during installation. Once restored, all thirty-two outputs operated normally. The repair took less than five minutes. Finding the wiring oversight had delayed startup by nearly two hours.

1746-OB32

1746-OB32

Transparency SOP: Quality Assurance & Testing

We don’t just ship boxes; we test them on actual Allen-Bradley SLC 500 racks.

• Inbound Inspection
  • Verify catalog number, hardware revision, and manufacturing labels.
  • Inspect the housing, terminals, PCB, and edge connector.
  • Screen for counterfeit markings and unauthorized repairs.
• Live Rig Testing
  • Install the module in a functioning SLC 500 chassis.
  • Verify processor recognition and diagnostic status.
  • Cycle all 32 outputs repeatedly under electrical load.
• Electrical Parameter Checks
  • Measure output voltage and current.
  • Verify switching speed and leakage current.
  • Confirm isolation performance and backplane current draw.
• Hardware Verification
  • Record hardware series and revision.
  • Confirm compatibility with supported SLC 500 processors.
• Final QC & Packaging
  • Perform a final functional inspection.
  • Clean connectors.
  • Package in anti-static materials with impact-resistant cushioning.

The Veteran’s Tech Trap Guide

⚠️ Don’t confuse the 1746- with the 1746-OV32. The is a sourcing module. The OV32 is a sinking module. Both fit the chassis, but they are not electrically interchangeable.

⚠️ Remember there are two output commons. Thirty-two outputs are divided into two groups of sixteen. Forgetting one common connection leaves half the module inoperative.

❗ Protect inductive loads. Solenoids and relay coils should always use flyback suppression. Repeated voltage spikes shorten transistor output life even when current ratings are respected.

⚠️ Verify total current, not just channel current. Individual outputs may be within specification while the common terminal exceeds its current rating. This is especially common after machine upgrades that add larger solenoid valves.

Always verify wiring, output polarity, and terminal assignments using the official Rockwell installation manual before applying power.

Frequently Asked Questions (FAQ)

Q1. Can the 1746- be hot-swapped?

No. The SLC 500 platform does not support live replacement of this module. Remove system power before installing or removing the card.

Q2. Is the 1746- a sourcing or sinking module?

It is a 32-point sourcing transistor output module designed for 5–50 VDC field devices. Systems requiring sinking outputs should use a different module, such as the 1746-OV32.

Q3. Is the 1746- still manufactured?

No. Rockwell Automation discontinued the 1746- on November 24, 2022. Most available units now come from verified surplus inventories or professionally refurbished stock.

Q4. Can the module drive solenoid valves directly?

Yes, provided the supply voltage and load current remain within the module specifications. For inductive loads, install appropriate flyback suppression to protect the output transistors.

Q5. Why are there two common terminals?

The 32 outputs are divided into two banks of sixteen outputs. Each bank has its own common terminal to distribute load current and simplify field wiring. Verify both commons are correctly wired during installation.

Q6. Are refurbished modules dependable?

Yes—provided every output channel is tested under load, switching performance is verified, and the module passes live rack testing before shipment. Cosmetic appearance should never be the sole acceptance criterion.

Q7. What warranty is typically offered?

Most established industrial automation suppliers provide a 12-month warranty on qualified new surplus and professionally refurbished 1746- modules. Warranty coverage generally applies to functional defects under normal industrial operating conditions.