SS823 Voting unit
Is SS823 necessary for a AC800M-HI system? for redundant power supplies, if I need one SS823 for each power supply or one for each redundant set?
Voted best answer
The AC 800M HI and the connected S800 I/O system (including field
power) must be supplied from a SELV or PELV power supply connected
through the power voter SS823. Older versions of AI880 (PR:B), DI880 (PR:B) and DO880 (PR:C), including field power, must be supplied from the SD821, SD822 or SD823 power supplies connected through the power voter SS823. (This restriction
is not valid for AI880A and newer versions of DI880 and DO880). If any field device connected to the AC 800M HI is externally powered, the device must be supplied from a SELV or PELV power supply connected through the power voter SS823.
Exception: When externally powered transmitters are connected to the analog input module AI880/AI880A via a fuse rated 60V/<= 0.1A, the SS823 can be omitted. This is valid for loops up to SIL2.
Therefore, for 2 redundant power supplies you need one SS823 power voter. See
"3BSE036351R5021 - AC 800M - Controller Hardware. Hardware and Operation" for more details how to connect SS823 to power supplies.
See also "3BSE034876R4101 - Reliability and Availability Data. AC 800M High Integrity".