POWER FAILURE TELEPHONE CALL SECURITY SYSTEM FOR TELEPHONE SYSTEM

摘要

PURPOSE:To secure a telephone call in a power failure and a telephone call when a power failure occurs in the middle by holding a trunk line at the time of the power failure by using office electricity feeding and transferring a trunk line telephone call to a telephone set for the power failure. CONSTITUTION:If a power failure occurs, a line terminating circuit 3 which operates by being fed with office electricity holds current trunk line communication and then while a main equipment 2 or master equipment connects the trunk line 1 to internal buses 12 and 13 directly, a telephone set for power failure 19 switches its internal extension telephone set circuit 15 to a telephone set circuit 14 which operates by being fed with the office electricity. Then the main equipment 2 or master equipment transfers the held trunk line telephone call to the power failure telephone set 19 to secure the trunk line telephone call during the power failure. Consequently, the construction for extra bus wiring for the installation of a large-capacity backup battery and the power failure telephone set is not required and the power failure telephone set can be installed at an optional point of the internal buses.