TNC &TNS Earthing System

What is the diversity factor?

Did you look at the code books?

Are you a student?

Your questions seem......................................................................curious.

TNC to TNS no problem (say it 3P+PEN to 4W (3P+PE and N) is olny separate between N and E

TNS to TNC is forbidden: Danger life parth exposed safety reason and for sure the upstream earth leakage will trip due to N and earth connected in TNC (PEN) with additional rods.

It's my understanding that TN-C is no longer used....

"The TN-C should be avoided since rank 3 harmonics and multiples of 3 flow in the PEN (added to neutral current) and prevent the latter from being used as a potential reference for communicating electronic systems (distributed intelligence systems). Moreover, if the PEN is connected to metal structures, both these and the electric cables become sources of electromagnetic disturbance.

Note

The TNC-S (TN-S downstream from a TN-C should also be avoided even though risks are smaller)."

http://www2.schneider-electric.com/documents/technical-publications/en/shared/electrical-engineering/dependability-availability-safety/low-voltage-minus-1kv/ect173.pdf

Because sooner or later, someone will get electrocuted.