OFFICE LINE CONNECTION CIRCUIT DURING SERVICE INTERRUPTIONS IN KEY TELEPHONE APPARATUS

摘要

OFFICE LINE CONNECTION CIRCUIT DURING SERVICE INTERRUPTIONS IN KEY TELEPHONE APPARATUS of the Invention A switching matrix in the key service unit of a key telephone system is formed by several groups of relays, each group being associated with a particular station set and each relay in each group also being associated with a particular central office line. All of the relays, except one in each group, disconnect the associated station set from the associated line when the relay is de-energized. One relay in each group functions in the opposite manner to connect the associated station set to the associated line upon failure of the local power supply.