Introduction to the Allen-Bradley 1746-OB32
When a legacy SLC 500 line goes down, every minute of downtime eats into production targets. The Allen-Bradley 1746-OB32 is a high-density digital DC output module built for exactly that environment. It packs thirty-two 24VDC output channels into a single slot, so you can drive more field devices without expanding your chassis. This module belongs to the SLC 500 series and installs in any available 1746 chassis slot except slot 0. It ships with a removable terminal block, a 32-LED status array, an octal door label, and a color-coded module bar.
Key Parameters That Matter on the Floor
Channel Density and Grouping
The 1746-OB32 provides thirty-two outputs split into two groups of sixteen points per common. That grouping simplifies wiring and lets you isolate faults to a single bank instead of the whole card.
Voltage and Current Behavior
The module sources 5-50 Volts DC with a nominal output of 24VDC. Each output point carries 0.5-0.25 amps, while the module handles 8 amps total and 2 amps per common. A minimum load of 1 mA per channel keeps signals stable.
Speed and Backplane Load
Signal delay is 0.1 ms ON and 1.0 ms OFF, with a step response of 60 milliseconds in and 2.5 milliseconds out. The module draws 190 milliamps from the 5 Volt backplane, so it will not strain your power budget.
Thermal and Environmental Limits
Heat dissipation reaches 0.172W per point and 6.45W for the whole module. Operating temperature spans 0 to 60 degrees Celsius at 5-95% non-condensing humidity. The unit withstands 30G operating shock and 2.5G vibration at 10-200Hz.
Comparison With Similar Output Modules
| Feature | 1746-OB32 | Typical 16-Channel DC Output | Typical 8-Channel DC Output |
|---|---|---|---|
| Outputs | 32 | 16 | 8 |
| Points per common | 16 | 8 | 8 |
| Nominal output | 24VDC | 24VDC | 24VDC |
| Backplane current (5V) | 190 mA | Lower | Lower |
| Signal delay ON | 0.1 ms | Similar | Similar |
| Best for | High-density panels | Mid-size racks | Small I/O counts |
If your panel is tight on slots, the 1746-OB32 replaces two 16-channel cards with one. That saves rack space, wiring time, and spare-part inventory.
Where the 1746-OB32 Fits Best
Panel Builders Tight on Slot Space
A machine builder adding pilot lamps, buzzers, and horns across a large panel can wire all 32 channels into one card. Fewer cards mean fewer connections and faster commissioning.
Legacy Line Upgrades
Plants running older SLC 500 systems often face obsolete 16-channel cards. Dropping in a 1746-OB32 keeps the existing chassis and field wiring intact while doubling density.
High-Current Actuation
The module suits high-current applications. It energizes solenoids, motors, and similar devices directly when they fall within the 5-50VDC range. For AC loads, add an interposing relay with a 24VDC coil, which also isolates the module from electrical noise in older wiring.
Installation and Setup Notes
Install the module in any 1746 chassis slot except slot 0. Use the supplied removable terminal block for clean termination. Allen-Bradley 1746-N3 or 1492 wiring systems fit this module and keep the door closed over the terminals. Avoid oversized wire, which crowds the front panel and blocks troubleshooting access. The output circuit isolation is tested at 1500V AC for one minute, protecting the backplane from field faults.
Maintenance and Reliability
Inspect the 32 channel LEDs periodically to confirm each output switches correctly. Check terminal torque and look for heat discoloration around the RTB. Keep the cabinet within the 0 to 60 degrees Celsius range and control humidity to 5-95% non-condensing. The 30G shock and 2.5G vibration ratings mean the card tolerates normal machine vibration, but mount it away from direct impact sources. Because the module carries C-UL and UL listings for Class I, Division 2, Groups A, B, C, D hazardous locations, follow your site’s safety procedures during any inspection. Please verify current lifecycle status and availability with SpareTechPLC before ordering.
Frequently Asked Questions
How many outputs does the 1746-OB32 provide?
It provides thirty-two outputs, arranged as two groups of sixteen points per common.
What is the output voltage range?
The module sources 5-50 Volts DC with a nominal output of 24VDC.
Can it drive AC devices directly?
No. For AC loads, use an interposing relay with a 24VDC coil so the module only switches the DC coil.
Which chassis slots accept this module?
Any available 1746 chassis slot except slot 0.
What wiring systems work with it?
Allen-Bradley 1746-N3 or 1492 wiring systems are compatible and keep the terminal door closed.
