Voting unit requirement

If we have two redundant power supply comming from UPS , connected to two different power supply unit (SD834) , what is the requirement of voting units.

Will it increase the system redundcany or any protection will be provided.

 Power Connection.jpg

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asked 1 month ago



Hi, only one Voting unit SS822 is needed. +24V,GND from both power supplies are connected at input of the Voting unit. Output +24V and GND from Voting unit is connected to power input of CPU, IO cards. The aim of 2 power supplies and Voting unit is to keep the control system powered even during plant shutdowns. It is increasing availability of the control system.

Connection of +24V between Voting unit and control system shoud be without fuse or circuit breaker. Circuit breakers shall be installed between power supplies and Voting unit.


answered 1 month ago


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The voting unit decides which power supply is used. The supply with the highest voltage is selected. It also prevents the higher voltage back feeding into the other power supply. (That would be a bad thing)

Rob Lyon   

answered 1 month ago


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