Product Overview

The Allen‑Bradley 1756‑PSCA2 is a specialized chassis adapter module designed to implement a redundant power supply architecture for the ControlLogix family of programmable automation controllers. As a critical component in high‑availability control systems, the 1756‑PSCA2 serves as the physical and electrical interface that enables two external redundant power supplies to deliver power to a single ControlLogix chassis backplane. This passive device occupies the power supply slot on the far‑left side of any standard 1756 chassis, including models 1756‑A4, 1756‑A7, 1756‑A10, 1756‑A13, and 1756‑A17 -4-6-11.

The 1756‑PSCA2 does not perform power conversion internally; rather, it functions as a passive bridge that funnels power from one or two redundant power supplies—such as the 1756‑PA75R (AC) or 1756‑PB75R (DC)—into the chassis backplane via the single power connector -4-6. In normal operation, the paired supplies share the chassis load automatically, extending the service life of each unit. In the event of a power supply failure, the remaining unit immediately accommodates the full load without any disruption to chassis activity -1-4. This design makes the 1756‑PSCA2 an indispensable element for critical infrastructure and process control applications where unplanned downtime carries significant financial or safety consequences. The module is available in a standard temperature variant (0°C to 60°C) and an extended‑temperature version, the 1756‑PSCA2XT, which is rated for -25°C to 70°C operation -2-3.

 

Technical Specifications

Parameter Name	Value
Product Model	1756-PSCA2
Manufacturer	Rockwell Automation / Allen‑Bradley
Product Type	Redundant Power Supply Chassis Adapter
Series	ControlLogix
Mounting Location	Left side of 1756 chassis (power supply slot)
Backplane Current (24V)	125 mA -6-10-11
Current Capacity (1.2V DC)	1.5 A -10-11-12
Current Capacity (3.3V DC)	4 A -2-3-10
Current Capacity (5.1V DC)	15 A -10-11-12
Current Capacity (24V DC)	2.8 A -10-11-12
Power Dissipation (Max)	25.7 W @ 30°C; 21.3 W @ 60°C -6-10-11
Operating Temperature	0°C to +60°C (32°F to 140°F) -3-6-10
Storage Temperature	-40°C to +85°C -6
Relative Humidity	5…95% noncondensing -2-3-12
Vibration	2 G @ 10…500 Hz -2-3-12
Shock (Operating)	30 G -2-3-12
Weight	Approx. 0.26 kg (0.56 lbs) -6-11
Enclosure Type	None (open‑style) -2-3-6
Certifications	Ex nA IIC T4 Gc (EN 60079-15), IECEx UL 14.0008X -10-11

 

Main Features and Advantages

Passive redundant power architecture: The 1756‑PSCA2 is a purely passive device, meaning it contains no active electronic components that could become points of failure -4-11. This design philosophy ensures exceptional reliability, as the module itself is excluded from the failure domain of the redundant power system. The 1756‑PSCA2 simply funnels power from the redundant supplies to the chassis backplane, providing a robust and maintenance‑free foundation for system uptime.

Automatic load sharing and seamless failover: When paired with compatible redundant power supplies, the 1756‑PSCA2 enables automatic current sharing between the two units under normal conditions, reducing thermal stress on each supply -1-4. Should one power supply fail, the remaining unit instantly assumes the entire chassis load without any interruption to processor or I/O operation. This zero‑downtime capability is essential for critical processes where even brief power interruptions can cause costly production stoppages or data corruption.

High current capacity for demanding systems: The 1756‑PSCA2 supports robust backplane current delivery, with ratings of 4 A at 3.3V DC and 15 A at 5.1V DC -10-11-12. This ample capacity ensures that even heavily populated chassis with multiple processors, communication modules, and high‑density I/O modules receive stable, regulated power under all operating conditions.

Versatile compatibility and global certification: The 1756‑PSCA2 is compatible with both AC and DC redundant power supplies, which can be mixed or matched in tandem configurations -4. It is certified to international standards including ATEX and IECEx for hazardous location operation (Ex nA IIC T4 Gc), making it suitable for deployment in environments where explosive atmospheres may be present -3-10-11. The module also features grounding provisions for application‑specific protective earth connections, ensuring compliance with global electrical safety requirements.

Extended temperature option: For harsh environmental conditions, the 1756‑PSCA2XT variant extends the operating temperature range from -25°C to 70°C, making it suitable for outdoor installations, unheated enclosures, or extreme climate applications -2-4.