Danish telephone plug
The plug consists of two vertical and one horizontal flat pin, arranged like 3 sides (left, right and top) of a rectangle. The two vertical pins carry the same tip and ring signals used in other countries. The third pin (top, horizontal) used to be connected to ground and was occasionally used with switchboards, but is now generally unused and left unconnected. Each pin is long, wide and about thick, compatible with one of the historic types of blade plugs. The two signal pins are apart while the ground pin is about above the center of the two signal pins. In practice, 5 variants of the plug are currently being made: Unlike in some other countries, this telephone plug was introduced long before any liberalization of the telephone market occurred. Until the mid-1980s, all legal telephone equipment with this plug was rented, purchased or at least approved from the regional telephone companies or (rarely) the government. The 3-pronged Danish Telephone Plug is a simplified form of an older 5 pronged plug, where the two extra pins (vertical, above and further apart than the signal pins) connected to a customer premises long life battery that provided power for telephones before the introduction of "automatic dialing" (the ability to place calls without operator assistance). Also in installations of similar age, a mechanical switch was sometimes installed behind the socket to allow manually switching the phone line between sockets in two locations within a building.
Technical description
The plug has 3 flat pins arranged at right angles to each other.