Tripolar plug

A tripolar plug-RJ11 adapter

The telefonic tripolar plug is the first type of telephone plug used in Italy. It has also been used in Finland, Norway and Turkey in older installations.

Structure

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.

Every plug complies with Italian standards. Formerly each of them was installed by SIP, now Telecom Italia, and had their trademark. Plugs without trademark exist also. Since 2007, Telecom no longer instals tripolar plugs in new electrical wiring systems.

In Finland, five-pin variant with second line also exists. Three-pin plug is compatible with five-pin socket.

Use

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.