The 1756-A13 is a 13-slot rack in the ControlLogix series produced by Allen-Bradley (Rockwell Automation) for mounting and organizing modules for the ControlLogix system. The rack is designed to support a variety of modules, including processors, power supplies, communication modules and I/O modules, to build a complete control system.

Here are some of the key features of the 1756-A13 rack:
Number of slots: 13 slots for various types of ControlLogix modules.
Power input: Supports multiple AC power input voltages.
Output voltage: Provides a stable output voltage for the ControlLogix control system.
Communication system: Supports ControlNet and EtherNet/IP networks, providing high-speed data transmission and remote device management.
Dimensions: According to the information provided, the dimensions are approximately 23.15 x 6.65 x 5.71 inches (another saying is 24 x 30 x 8 inches).
Weight: About 4.2 pounds (1.9 kg).
Installation: Usually installed in the control cabinet to provide structural support for the ControlLogix system.
Compatibility: Compatible with a variety of ControlLogix modules, including but not limited to processor modules such as 1756-L71, 1756-L72, 1756-L73, 1756-L74, 1756-L75, and power modules such as 1756-PA72, 1756-PB72.
The 1756-A13 rack also features advanced features such as time stamping for SOE (Sequential event recording) applications, as well as enhanced security features including digitally signed controller firmware, controller-based change detection, and more.