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With PM891 CPUs only: up to 100 per RNRP Area
Any other configuration of PM8xx CPUs: up to 50 per RNRP Area
Max permitted number of controllers per OPC server is another question.
Please download documents from ABB Library, eg the System Guide and the Network Configuration Guide.
800xa 6.0 is 48 controller per CS (Max 48 (can be less depending on data throughput needs)
800xa 5.1 12 to 48 as per CS application size calculation
Instead of using the default rule of 12 controllers per Connectivity Server, a load calculation using the optimized rule can be performed, which may allow up to 48 controllers per Connectivity Server
When u are talking about the RNRP limitation in turn it will talk about the 800xA system limits.
ex"For class B network for say area 1 172.16.4*1.x/22 you can use upto 1022 nodes but in this tested RNRP nodes to use are 500(256 to 500 spare RNRP nodes) nodes only and this includes your Rich clients, controller nodes, servers(application,As,CS,Domain)
So by looking at this while selecting larger system 800xA(tested)can support up to 80 clients per network area of node range 71-150
and controller nodes will depend on the size of the applications per 800MCS so you can connect max of 80 per system so on thumb rule you can connect 8*10 controllers/CS
of node range 151-255
It means you have design ur network based on the system limitation not based default network class.