Abstract: A waterproof electrical connection apparatus having a plug casing which is inserted into a socket casing. The socket casing is provided with a hinged protective cover which is movable between an open position and a closed position. The socket casing can be used as an outlet or the connector of an extension lead of an appliance coupler. The socket casing has on an upper portion an annular groove intended to receive a singular annular seal which extends from the groove in an axial direction. The annular seal has a hooked-shaped cross-section which extends towards the interior of the socket casing. The cover and the plug have meeting surfaces intended to come into contact with the seal when the cover is in a closed position and when the plug is coupled to the socket.