Hybrid and modular plug systems comprised of electrical plugs, adapter plugs, plug connectors and earth plugs for use with electrotechnical, electronic, optoelectrical and optical apparatuses and components; modular plugs for power, data and light signals, in particular hybrid plugs in the nature of plug-in connectors for simultaneous connection of power, data and optical fiber lines; plug-in connectors; insulated electrical plug-in connectors; plug-in connectors for optical fiber lines; elec...