Why Engineers Specify the 1746-P3 for SLC 500 Racks
When an SLC 500 chassis loses backplane power, the whole line stops. The Allen-Bradley 1746-P3 is the dedicated power supply that keeps that backplane alive. It mounts at the left side of the 1746 chassis and does not occupy a slot, so you keep every I/O position available for control modules.
This unit takes a nominal 24 VDC input and converts it internally to the voltages the rack needs. If you are maintaining an existing SLC 500 system, this is the practical replacement path rather than a full platform migration.
Technical Specifications
| Parameter | Value |
|---|---|
| Input Voltage Range | 19.2-28.8 VDC |
| Nominal Input Voltage | 24 VDC |
| Backplane Current (5 VDC) | 3.6 A |
| Backplane Current (24 VDC) | 0.87 A |
| Typical Line Power Requirement | 90 VA |
| Inrush Current | 20 A |
| Isolation Voltage | 600 VAC RMS for 1 s (version B or later) |
| Hold-Up Time | 5 ms (full load); 1000 ms (no load) |
| Fuse Protection | 1746-F3 or equivalent |
| Operating Temperature | 0…60 °C (32…140 °F) |
| Current Capacity Deration | 5% above 55 °C (131 °F) |
| Dimensions | 139.7 x 79.2 x 144.8 mm |
| Weight | 1.1 kg (2.5 lb) |
What the Numbers Mean on the Floor
The 3.6 A at 5 VDC and 0.87 A at 24 VDC figures tell you how many modules the rack can support. Add up your module load before you swap a supply, because an undersized supply causes intermittent faults that look like logic problems. The 19.2-28.8 VDC window gives you headroom on a nominal 24 VDC bus. Hold-up time of 5 ms at full load and 1000 ms at no load keeps the CPU running through brief voltage dips.
Where This Supply Fits
The 1746-P3 suits SLC 500 modular control systems in oil, gas and general industrial automation. Typical scenarios include remote wellhead panels running on 24 VDC, pipeline monitoring racks, and water treatment skids where a stable backplane is critical. In each case the supply sits at the left of the chassis and feeds every module in the rack.
Installation and Setup
Mount the unit in the left-most position of the 1746 chassis. You need only a 1/8 inch flat head and a 1/4 inch Phillips head screwdriver. Keep the module in static-shield packaging until installation, and avoid touching connector pins or circuit components. There is no isolation between the backplane and input terminals, but a dielectric withstand of 600 VAC RMS for 1 second exists between chassis ground and input terminals. The pre-installed fuse may be replaced with a 1746-F3 or equivalent.
Reliability and Maintenance
Inspect the supply periodically for dust buildup and secure connections. The operating range is 0…60 °C, with current capacity derated 5% above 55 °C, so verify cabinet ventilation in hot climates. The unit is rated for altitudes up to 2000 m without derating and for Pollution Degree 2 environments. Keep a spare fuse and a spare supply on the shelf to avoid extended downtime.
Selection Checklist
Before ordering, confirm your input is 24 VDC nominal within 19.2-28.8 VDC, total your 5 VDC and 24 VDC module loads, and check the chassis position. UL and C-UL listings cover Class 1, Division 2, Groups A, B, C, D hazardous locations. For hands-on selection help and fast dispatch, contact Oil AutoTech today for pricing and availability.
