The Allen-Bradley 1791-8BR is a Compact block I/O module. This module is a combination module that features Eight (8) 24VDC inputs and Eight (8) Normally Open (N.O.) contact outputs. This module has a rackless design, installed directly to a standard DIN rail or directly panel mounted. It comes with a built-in power supply, communication interface, I/O interfaces and corresponding signal conditioning circuitry.

The 1791-8BR supports Remote I/O (RIO) protocol for interfacing with controllers and RIO scanners. With its compact design and built-in components, the 1791-8BR is capable of functioning as a stand-alone distributed I/O station. It may be installed near the input and output devices in the field to eliminate long cable runs.

The 1791-8BR, similar to any other Block I/O module, are compatible with PLC and SLC automation product families. Specifically, the 1791-8BR are compatible for use with PLC- Family scanner modules such as 1771-SN and 1772-SD / 1772-SD2; Any PLC-3 scanner modules and 1775-S5, or 1775-SR5 module from the PLC3 family and PLC-5VME (6008-LTV) module.

Incoming power connections are made via terminals +24 (1), RET +24 (3) and GND (2). Remote I/O (RIO) connections are made via terminals BLU (6), CLR (8) and SHD (7).

Compatible input devices for the input channels of the 1791-8BR are proximity switches, limit switches, selector switches, float switches, pushbutton switches, auxiliary contacts and other binary signaling devices. Compatible output devices are solenoid actuated devices, motor starters, inductive and resistive loads. The 1791-8BR does not come with internal fusing. Appropriate external protection may be installed as needed.

This module receives DC power as an input and delivers AC power as an output. There are 8 inputs per block on this module. Additionally, this module's outputs are in one group with a normally open relay. The 1791-8BR has three different outputs voltages: 20 to 132 Volts AC, 20 to 30 Volts DC, and 125 Volts DC. These differences are caused by the characteristic of the output that depends on the load. Hence, other ratings are varied as well. Examples of other parameters a output current rating, power rating, and surge current. Among these parameters, the most critical parameter is surge current. You need to pay attention to the surge current of this output and the devices it is connected to because this module does not have a surge limiting current. You need to use external fuses to prevent any damage. This action is necessary because even if this module has internal protection, this internal protection is able to protect the circuit inside the module only. The external circuit is not protected by this internal protection. When terminating signal wires to the Block I/O module, use 14-gauge stranded wire with 3/64 maximum insulation thickness. Increase load current by using a high-quality conductor with low resistance. Parallel output connections is not permitted as this lowers the overall circuit resistance.