Manual Intercom Line

A 401-type card provides a manual intercom circuit. It provides the battery necessary for the talking path and control of the lamps associated with the line to indicate when the line is in use.

The 401-type card also has a spare set of relay contacts. These can be used to operate auxiliary devices, such as a paging amplifier.

The 401-type KTUs are four inch cards with 18 contacts.

The most common 401-type card is the 401A, followed by the 401B.

Below is the "Condensed Functional Schematic of 401A KTU (Manual Intercom Line Circuit)" from issue 4 of section 518-215-402 updated in December 1979 from Volume II of the New Jersey Bell Key Systems Service Manual.