Allen‑Bradley 1790D-T8A0 120V Input Module

Allen‑Bradley 1790D-T8A0 8 Input 120V ac Base Module

Product Introduction

The 1790D-T8A0 from Allen‑Bradley provides eight digital AC input channels in a compact DeviceNet base module. It accepts nominal 110V ac to 120V ac inputs, with a wide operating range from 85V ac to 132V ac at 47‑63 Hz.

Additionally, this module features an input impedance of 18 KΩ and a maximum on‑state current of 9 mA at 132V ac. The off‑state voltage threshold is 45V ac maximum, which ensures reliable distinction between on and off signals. Each input includes a green status LED for visual confirmation.

Therefore, the 1790D-T8A0 suits applications where you need to monitor AC field devices. For example, you can connect AC limit switches, pushbuttons, relay contacts, or AC proximity sensors. Meanwhile, the 8 points/8COM design gives each input its own dedicated common terminal.

Technical Specifications (AC Input Characteristics)

• Inputs per module: 8 points, non‑isolated between inputs

• On‑state voltage range: 85V ac min, 110V ac nom, 132V ac max

• Input impedance: 18 KΩ (key parameter)

• On‑state current (max): 9 mA at 132V ac

• Off‑state voltage (max): 45V ac

• Input signal delay: Off to On = 10 ms, On to Off = 30 ms

• Indicators: 8 green input status LEDs (one per channel)

• Common type: 8 points / 8 COM (each input has its own return)

The dedicated common per input (8 points/8COM) eliminates shared return wiring issues. You can independently wire each input to its own AC neutral or return path. This design simplifies troubleshooting and reduces crosstalk between channels.

General & Power Specifications

• DeviceNet power supply: 24V dc nominal (range 11‑28.8V dc)

• DeviceNet power dissipation: 1.2W max at 28.8V dc

• External AC power supply: 110V rms, 60 Hz nominal (range 85‑132V rms, 47‑63 Hz)

• External AC power dissipation: 3W at 132V ac

• Isolation:

  • I/O to logic: photocoupler isolation, 1250V ac rms (key parameter)

  • Field power: non‑isolated

• Wiring terminal block: M3.0 screw type, torque 7 lb‑in max (use copper or copper‑clad aluminum conductors)

• Recommended fusing: 1A, 250V, normal blow (external)

The photocoupler isolation protects the DeviceNet logic side from AC line transients. However, the AC field power circuit is not isolated from the inputs. Therefore, you should install the recommended 1A fuse on the AC supply line for safety.

Mechanical & Environmental Information

The 1790D-T8A0 mounts on a standard DIN rail or panel. It operates reliably from 0°C to 55°C ambient temperature. Storage temperature ranges from -40°C to 85°C. Humidity tolerance is 5‑95% non‑condensing.

Furthermore, this base module consumes only 1.2W from the DeviceNet supply plus up to 3W from the AC field supply. Total heat dissipation remains low, so no forced cooling is required in most cabinets.

Installation Guidelines

First, disconnect both DeviceNet power and external AC power. Next, mount the 1790D-T8A0 on a DIN rail or using panel mounting screws.

For wiring, use copper conductors sized 0.5‑1.5 mm² (20‑16 AWG). Tighten each M3 screw to 7 lb‑in maximum. Connect the external AC supply to the designated AC power terminals. Install a 1A, 250V normal‑blow fuse on the AC line input as recommended.

Then connect each AC field device between an input terminal and its corresponding common terminal. Because each input has its own common (8 points/8COM), you do not need to share return wires. Connect the DeviceNet cable to the module's pass‑through connectors.

Finally, apply AC field power first, then apply DeviceNet power. Verify that the green LEDs light correctly when each input receives 110‑120V ac.

Packaging List (Per Unit)

• 1790D-T8A0 8 Input AC Base Module – 1 pc

• Terminal block (pre‑attached) – 1 pc

• Quick start guide (printed) – 1 pc

• Dust cover – 1 pc

Note: No certificates or warranty documents are included in the package. Fuse not included.

Shipping & Delivery

We ship worldwide via FedEx, UPS, or DHL. All modules are packed in anti‑static and anti‑shock materials. Tracking number will be provided within 24 hours after dispatch.

Frequently Asked Questions (FAQ)

1. Can I use the 1790D-T8A0 with 230V ac inputs?
No. The maximum on‑state voltage is 132V ac. Applying 230V ac will permanently damage the input circuit. Use the 1790D-T8A0 only with 110‑120V ac systems.

2. Why is the off‑to‑on delay 10 ms but on‑to‑off delay 30 ms?
The longer off‑to‑on delay (30 ms) provides filtering against AC line noise and contact bounce. This design ensures stable signal detection for standard industrial AC switches.

3. Do I need an external fuse for each input?
No. The recommended 1A, 250V fuse should be placed on the main external AC power supply feeding the module. Individual input fuses are not required.

4. Can I mix AC and DC inputs on the same 1790D-T8A0?
No. This module accepts only AC inputs (85‑132V ac). For DC inputs, please consider the 1790D-T32BV0 or other 1790D series DC input modules.

5. What happens if I connect the AC supply backwards?
Because AC has no polarity, reversal does not damage the module. However, ensure proper grounding and follow local electrical codes for safety. The module will function correctly regardless of line/neutral orientation.