The Allen-Bradley 1746-A4 is an expansion module constructed with 4 slots and mounting tabs to house modules from series SLC 500. This part itself belongs in the series SLC 500 A Modular Chassis. This panel-mounted rack needs its own power supply which will be mounted on the left end panel (power supply support panel) with screws. The right end and center panels are kept still by a latch, and therefore don’t require any screws. Install the chassis on the enclosure by securing 4 holes for the mounting tabs.  To allow an electric path between the chassis and the back panel, it may be necessary to scrape some of the paint off.

The 4-slot 1746-A4 Modular Chassis may be applied in a configuration with multiple chassis or as a single unit configuration. When used alone, keep the connector plug of the chassis on the left side. Up to three chassis can be joined together using the chassis interconnect cable. This setup creates 30 I/O slots, maximum. Take note that different installation layouts will require a different cable. When connecting chassis side-by-side, use the 1746-C7 cable which is 152.4 millimeters (6 inches) in length. To station one chassis below the other, choose from the 14.4 millimeter (36 inch) long 1746-C9 or 1.27 meter (50 inch) long 1746-C16.

The 1746-A4 has a maximum backplane current of 5.1 Volts DC at 10 A and 24 Volts DC at 2.88 A. Without the modules, it weighs approximately 0.75 kilograms (1.7 pounds). It measures 17.7 x 17.1 x 14.5 centimeters (7.1 x 6.8 x 5.8 inches) and operates in temperatures between 0 and 60 degrees Celsius (32 to 140 degrees Fahrenheit), with a relative humidity of 5% to 95% (without condensation).