The schematic is not my work, so I don't want to upload it.
I know that the CPU is used in a unearthed DC control circuits (IT systems).
This mean that a CPU 31xC is not suitable, right?
I should use a CPU with ungrounded reference potential (CPU with grounding slide contact).
This way a RC network is in between the protective conductor and the rail. My insulation resistance should then be the R (of the RC network) value then?
I also want to know what problem I could expect when using a Siemens S7-300 CPU ungrounded. Like in my case. CPU312C-tape(isolation)-rail .