Hello Jose,
In fact connection objects have their own enhancement technique, which is the same as products master data (they use set types). So if you want to add z fields to IS-U tehnical objects (connection objects, premises and point of delivery) you need to read the corresponding cookbook available on service.sap.com/utilities. You can also check the following IMG:
SPRO >> CRM >> Industry specific solutions >> Utilities >> Technical objects >> Enhancements.
Regards,
Nicolas