Allen-Bradley 1791-8AC I/O Block 8 In 8 Out

Allen-Bradley 1791-8AC 8-In 8-Out 120VAC Block I/O Module

Product Introduction

The Allen-Bradley 1791-8AC is a combination Block I/O module. It offers eight discrete 120VAC input channels. It also provides eight discrete 120VAC output channels. You can use this module for distributed I/O solutions. The module supports the Remote I/O (RIO) protocol. A built-in power supply and PLC interface are included. Signal conditioning circuitry is also embedded inside.

Technical Specifications – Inputs

The 1791-8AC has eight 120VAC input channels. These channels are arranged in one single group. The on-state voltage range runs from 79 to 132VAC. Minimum on-state current is 5 mA at 79V. Off-state voltage stays below 35V maximum. Off-state current is 2.3 mA minimum.

External power for the module needs 85 to 132VAC at 150 mA. This power energizes the entire module and its internal backplane.

Technical Specifications – Outputs

The 1791-8AC provides eight 120VAC output channels. Output voltage range runs from 20 to 123VAC. Output current rating depends on mounting orientation and temperature.

For vertical mounting at 30 to 60°C, output current is 300 to 600 mA per channel. For horizontal mounting at 30 to 60°C, output current is 150 to 300 mA per channel. Surge current reaches 10 Amps for 50 milliseconds. This surge can recur every 2 seconds. Minimum on-state output current is 50 mA per output.

Maximum voltage drop is 1.5V at 300 mA. Off-state leakage current is 3 mA maximum. Output signal delay time is 1 ms for off-to-on at 60 Hz. On-to-off delay is 8.3 milliseconds.

Power and Thermal Ratings

The 1791-8AC has a maximum power dissipation of 12.9 Watts. Thermal dissipation reaches 43.99 BTU/hr. These ratings allow operation in standard industrial panels.

Isolation and Protection

Isolation voltage is 500 VAC tested at 1250 VAC. This applies to I/O group-to-group isolation. It also applies to I/O group-to-logic isolation. Proper isolation ensures reliable operation in noisy environments.

Communication and Remote I/O

The 1791-8AC functions as an RIO adapter only. It sends input updates to the processor on the RIO network. It also receives control commands to actuate output channels. The module uses Belden 9463 cable for the RIO link. A daisy chain topology is standard for these blocks.

Additionally, BTR and BTW instructions send up to 32 arrays of read and write messages. You can connect these in parallel for larger message volumes.

Compatibility

The 1791-8AC works with legacy Allen-Bradley controllers. Compatible platforms include the PLC-2, PLC-3, and PLC-5 families. It also works with RIO-enabled SLC 500 processors. For SLC systems, you need the 1747-SN Remote I/O scanner module.

Mechanical Dimensions and Mounting

The 1791-8AC measures 176.5 x 68.8 x 98 mm. This equals 6.95 x 2.7 x 3.85 inches. The module weighs approximately 0.43 kg (0.94 lbs). You can mount it vertically or horizontally. Mounting orientation affects output current ratings as noted above.

Removable terminal strips are located on both sides. They handle input, output, RIO, and power connections. Status indicators let you monitor I/O and communication states.

Packaging List

• 1791-8AC module (1 unit)

• Removable terminal strips (left and right)

• User manual quick start guide

Note: No certificates or warranty documents are included in the package.

Frequently Asked Questions (FAQ)

1. How many inputs and outputs does the 1791-8AC have?
It has eight 120VAC inputs and eight 120VAC outputs. All channels are in one group.

2. What cable is required for the RIO connection?
Use Belden 9463 cable for the Remote I/O link. A daisy chain topology is recommended.

3. Does mounting orientation affect the 1791-8AC performance?
Yes, output current ratings change with orientation. Vertical mounting allows higher current (300-600 mA) than horizontal mounting (150-300 mA) at 30-60°C.

4. Which controllers work with the 1791-8AC?
It works with PLC-2, PLC-3, PLC-5, and RIO-enabled SLC 500 processors using the 1747-SN scanner.

5. Which shipping carriers do you use?
We ship via FedEx, UPS, and DHL for fast and reliable delivery worldwide.