Description
Product Introduction
The Allen-Bradley 1746-IA8 is an 8-point 120V AC digital input module designed for the SLC 500 programmable logic controller system. Installed directly into any available slot of a 1746 chassis (such as a 1746-A7 or 1746-A10 backplane), the module provides interface connections between high-voltage 120V AC field devices and the low-voltage logic processing of the SLC CPU.
Featuring optical isolation between field circuitry and backplane logic, the 1746-IA8 protects the main processor from electrical noise, line surges, and field-side transients. Its low-density 8-point configuration with a front-facing LED indicator array makes it ideal for legacy installations requiring robust 120V AC control loops.
Key Technical Specifications
| Parameter | Specification |
| Manufacturer Part Number | 1746-IA8 |
| Number of Inputs | 8 Digital AC Inputs |
| Voltage Category | 100/120V AC |
| Operating Voltage Range | 85 to 132V AC at 47–63 Hz |
| Off-State Voltage (Max) | 30V AC |
| On-State Current (Min) | 5.0 mA at 85V AC |
| Backplane Current Draw | 50 mA at 5V DC / 0 mA at 24V DC |
| Signal Delay (Max) | Turn-On = 35 ms, Turn-Off = 45 ms |
| Points per Common | 8 Points on 1 Common |
| Operating Temperature | 0°C to 60°C (32°F to 140°F) |
Application Scenarios & The “Trench” Experience
It is 4:45 PM on a Friday at a municipal water treatment plant. A main pump control panel loses feedback status on Input Bit 3, halting the automated reservoir fill cycle. The shift electrician suspects a blown optocoupler channel on an aging 1746-IA8 card. Because the 1746 platform uses removable terminal blocks, the electrician flips the power off, unclips the wiring arm with field leads intact, swaps the bad card with a bench-tested 1746-IA8 from spares, snaps the terminal block back into place, and powers up—restoring full operation in under 10 minutes without touching a single field wire screw.
- Legacy Panel Maintenance – Motor Starter & Contactor Aux Contacts – Monitors 120V AC auxiliary feedback contacts on heavy industrial starters.
- Material Handling & Conveyor Lines – Heavy-Duty Limit Switches – Reads high-voltage mechanical limit switches and E-stop circuit monitors.
- Retrofit Upgrades – SLC 5/03, 5/04, 5/05 Systems – Replaces damaged or degraded AC input channels in existing control cabinets.
Transparency SOP: Quality Assurance & Testing
We don’t just ship boxes; every 1746-IA8 module undergoes rigorous diagnostic testing prior to dispatch.
- Inbound Physical & Terminal Audit: Inspected housing plastic, backplane edge connector pins, and terminal block screw threads for damage or corrosion.
- Backplane Logic Verification: Installed into a live 1746-A10 chassis; confirmed 50 mA backplane current draw and CPU module detection without backplane errors.
- 8-Channel Voltage Threshold Testing: Applied 120V AC inputs to each of the 8 channels individually; verified LED state illumination and RSLogix 500 input data table updating (
I:e.0throughI:e.7). - Off-State Leakage & Isolation Test: Tested off-state voltage threshold (<30V AC) to ensure no false triggering occurs from induced line capacitance or stray voltages.
- ESD Protection & Packaging: Cleaned, sealed in static-shielding wrap, and packed inside padded protective shipping cartons.
- 1746-IA8
- 1746-IA8
The Veteran’s Tech Trap Guide (Crucial Value-Add)
- ⚠️ Mind the 35ms Input Filter Delay!
The 1746-IA8 has an inherent hardware input signal delay of 35 ms (turn-on) and 45 ms (turn-off) to filter out AC sine wave zero-crossing noise. Do not use this module for high-speed application timing (such as fast pulse counting or part presence registration); use high-speed DC modules or a counter card like the 1746-HSCE instead.
- ❗ Never Hot-Swap Modules in a 1746 Chassis!
Like all SLC 500 modules, inserting or removing the 1746-IA8 while the 1746 power supply is turned on will cause electrical arcing, potential memory corruption, or damage to backplane driver ICs. Always isolate main rack power prior to replacing cards.
- ⚠️ Watch Out for Leakage Voltage on Long Cable Runs
Parallel 120V AC field wiring runs in long conduit can couple inductive or capacitive voltage onto the signal wire. If the stray off-state voltage exceeds 30V AC, the 1746-IA8 channel may remain stuck ON. Install a resistor or loading cable across the input terminals to bleed off leakage current if necessary.
- ❗ Verify Common Terminal Connections
All 8 channels on the 1746-IA8 share a single common return line (Terminal 9). Ensure the neutral side of your 120V AC field power circuit is landed correctly on the common terminal to complete the input circuit loop.
Frequently Asked Questions (FAQ for Conversion)
Q: What is the difference between 1746-IA8 and 1746-IA16?
A: The 1746-IA8 provides 8 digital AC inputs on 1 common terminal, whereas the 1746-IA16 provides 16 digital AC inputs on 1 common terminal within the same single-slot module footprint.
Q: Can I use 24V DC inputs on a 1746-IA8 card?
A: No. The 1746-IA8 is strictly an AC input card designed for 85–132V AC signals. Applying 24V DC will not trigger the input circuit. For 24V DC inputs, use a 1746-IB8 or 1746-IB16 module instead.
Q: Does the 1746-IA8 come with the removable terminal block (RTB)?
A: Yes, all our New Surplus and Refurbished 1746-IA8 modules include the front removable terminal block assembly.
Q: Are 1746-IA8 modules still manufactured by Allen-Bradley?
A: The SLC 500 series has matured into legacy/discontinued status by Rockwell Automation. We maintain extensive inventory of certified New Surplus and fully bench-tested, refurbished original 1746-IA8 modules.
Q: What warranty comes with this module?
A: Every Allen-Bradley 1746-IA8 module comes with a full 12-month replacement warranty. If any channel or backplane interface fails under standard operating conditions within one year, we replace it immediately from stock.
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