Tripolar plug

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The telefonic tripolar plug is the first type of telephone plug used in Italy.

[edit] 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, is used only for parallel circuit uses.

Every plug complies with Italian standards. Formerly each of them was installed by SIP, now Telecom Italia, and had their trademark. Now plugs without trademark exist also.

[edit] Use

The tripolar plug is being 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.