Under the name of "CEE connectors" most medium industrial appliances use connectors according to the IEC 60309 standard.
Mennekes had a background in the design of charging couplers based on the IEC 60309 standard (CEEform plugs) including variants like the CEEplus that included additional signal wires.
IEC | ISO/IEC 7816 | IEC 62056 | ISO/IEC 42010 | ISO/IEC 15693 | IEC 60320 | IEC 60309 | ISO/IEC 8859 | ISO/IEC 7810 | ISO/IEC 646 | ISO/IEC 24744 | IEC's | IEC 62196 | IEC 61131 |