Viega Multiplex Trio E Instructions For Use Manual page 24

Handling
Fasten the control element from below with a union nut.
Place the site protection on the control element.
Lead cable with cable lead-in into the recess in the right-hand side
of the casing of the mixing unit.
Connect the plug of the cable leading to the control element to the
connection of the control unit marked "TLI A".
The plug has a groove left and right on one long side which must
face forward when plugging in.
Set the casing lid on the mixing unit and screw it down.
Multiplex Trio E fitting, electronic mixing unit 24 from 38