The ABB SS822​ is a specialized Power Voting Unit manufactured by ABB, designed for the highest levels of system availability and fault tolerance, particularly in Safety Instrumented Systems (SIS) and critical process control. It functions as a triple modular redundant (TMR) power supply and distribution module. The unit accepts three independent input power sources, performs intelligent monitoring and “voting” on their health, and delivers a single, ultra-reliable fused and conditioned power output to critical loads, eliminating any single point of failure in the power path.

In a hazardous chemical reactor, the Safety Instrumented System (SIS) that executes emergency shutdowns is built on a Triple Modular Redundant (TMR) architecture, where three separate controller channels must vote on any shutdown action. For this to work, each controller channel requires absolutely reliable, clean power. Using three standard power supplies introduces three separate points of potential failure. The ABB SS822​ Power Voting Unit is installed as the common power source. It is fed from three physically separate and independent 24VDC supplies, perhaps from different subpanels or even different UPS systems. Inside the SS822, advanced circuitry continuously monitors all three inputs for voltage level, ripple, and integrity. Using a hardware-based voting logic, it selects the best available power source and routes it through its output fuses to the TMR controllers. If one input fails, the unit seamlessly and instantaneously switches to a healthy input with zero interruption. This ensures the SIS controllers remain powered under nearly any single power supply fault, directly addressing the paramount requirement for power availability in life-critical and production-critical safety systems.