Why the 1746-P1 Remains the Backbone of Your SLC 500 Rack
When a legacy SLC 500 line goes down, the power supply is almost always the first suspect. The Allen-Bradley 1746-P1 is the module that feeds every card in the chassis. Without it, no processor scans, no I/O updates, and no production output. This power supply accepts a nominal input of 120/220 Volts AC and converts it into the internal rails your modules depend on.
Engineers who maintain aging control cabinets know the drill. A single failed supply can idle an entire cell. The 1746-P1 solves that problem by delivering a steady 2 A at 5 VDC and 0.46 A at 24 VDC to the backplane. It also provides a 24 VDC output with built-in fuse protection, so a short circuit does not become a fire hazard.
Inside the 1746-P1: Key Ratings That Matter
The 1746-P1 is not a generic power brick. Rockwell Automation built it specifically for the 1746 chassis, and its ratings reflect that focus.
Input and Output Behavior
The module runs on 120 to 220 Volts AC input with a frequency range of 47 to 63 Hertz. Input power sits at 42 Watts, and inrush current peaks at 20 Amps. That inrush figure matters during startup, because undersized upstream breakers can nuisance-trip when several supplies energize at once.
On the output side, the 1746-P1 holds an output voltage range of 18 to 30 Volts DC. The backplane current reaches 2 Amps at 5 Volts and 0.46 Amps at 24 Volts. These are the exact figures you should compare against your total module load before adding cards.
Physical and Environmental Fit
The unit measures 5.5 x 2.3 x 5.7 inches and weighs 2 pounds (0.9 kilograms). It operates between 0 and 60 degrees Celsius. Above 55 degrees Celsius, the current capacity derates by 5%, so cabinet thermal management directly affects how much headroom you keep.
Where the 1746-P1 Earns Its Keep
Replacing a Failed Supply in a Running Line
A food processing plant running an SLC 500 main rack sees intermittent CPU faults. The cause is often a tired supply that can no longer hold voltage during brownouts. The 1746-P1 keeps the controller alive through short dips, with a CPU hold-up time of 20 ms at full load and 3000 ms at no load. That window is enough to ride through many utility blips without losing the program.
Expansion Rack Power
Whether you run a main, expansion, or Remote I/O rack, the installation position is the same. The supply sits at the leftmost slot, and only one unit is needed per chassis. That single-supply rule simplifies spares planning and reduces the number of part numbers your storeroom must carry.
Installation Notes for a Clean Startup
Set the input jumper before you apply power. The exposed pins carry hazardous voltage once energized, and an incorrect jumper setting can damage the supply or injure personnel. Confirm your line voltage falls within the 120 to 220 Volts AC nominal range and that frequency stays between 47 and 63 Hertz.
Mount the module in the leftmost position of the 1746 chassis. Verify that the fuse is intact; the correct replacement is the 1746-F1 or an equivalent. Remember that fuse protection guards against fire from short circuits, not against every user-power overcurrent event. For user-power faults, behavior differs by build origin, so consult your specific unit’s documentation before assuming a recovery path.
Maintenance and Long-Term Reliability
Inspect the supply periodically for discoloration, loose connections, and dust buildup that restricts airflow. Heat is the enemy here. Keep cabinet temperature below 55 degrees Celsius to avoid the 5% derating and extend capacitor life. Because the 1746-P1 is a mature SLC 500 component, verify current lifecycle status and availability with SpareTechPLC before you commit to a long-term spares strategy. A consulting-minded buyer confirms stock now rather than waiting for a line-down emergency.
Integration with Your Existing System
The 1746-P1 integrates directly into any 1746 chassis and powers the modules attached to it. It does not require external communication configuration because its job is purely electrical. If your rack already runs SLC 500 processors and I/O, this supply is a drop-in electrical foundation, provided your total current draw stays within the 2 A at 5 VDC and 0.46 A at 24 VDC limits.
What to Verify Before You Buy
Check three things. First, confirm your input voltage matches the 120 to 220 Volts AC nominal rating. Second, total your backplane current demand and leave margin. Third, confirm the fuse type and have a 1746-F1 or equivalent on hand. When you source through SpareTechPLC, you get a focused industrial automation supplier that understands these checks matter more than a low sticker price.
