What does the "P" at the end of a unit description stand for, e.g. on PNOZ X3P?

The "P" at the end of a unit description stands for "pluggable", i.e. for types with plug-in connection terminals.

There are two types: plug-in screw terminals and plug-in push-in spring-loaded terminals. The spring-loaded terminals are identified by the "C" in the unit description, e.g. PNOZ X3P C.