Tripolar plug

It has also been used in Finland, Norway and Turkey in older installations.

It uses three pins: the two on the top are joined with the twisted pair of cables bringing the signal; the third, off-center, can be used for loop through when more sockets exist.

In Finland, the third pin is earth ground, but it is rarely connected.

Since 2007, TIM no longer installs tripolar sockets in new electrical wiring systems.

The tripolar plug has been supplanted by the international RJ11 standard, both because it is more diffused in new technology devices and because the tripolar plug isn't suitable for ISDN.