COLLECTIVE HOUSING INTERCOM SYSTEM AND SYSTEM EXPANSION DEVICE

摘要

PROBLEM TO BE SOLVED: To provide a collective housing intercom system allowing simultaneous communication using main lines of plural systems while reducing a loss on main lines of the systems.SOLUTION: The collective housing intercom system having a communication channel includes: sub-main lines of plural systems in which one or plural dwelling unit terminals which are branched therefrom and connected thereto; and a main line in which the sub-main lines of the plural systems are branched therefrom and connected thereto via plural branching devices. Each of the plural branching devices includes: a pair of main line connection sections which are inserted in series along the main line; a sub-main line connection section to which the sub main lines to the system expansion device are connected; and a branching circuit for branching a signal flowing a pair of main line connections to the sub-main line connection.