I am suitable for the large-scale spot on a ringing tone expansion buzzer and a summons indication turn light.
It is mutual, and parent and child type, a compound expression can use even a system of either.
Is more than two sets at the same time; can talk, and interrupt it, and the call is possible, too.
For terminal terminal with a table, the wiring is easy, too.
Other various switchboards
＊Light, power switchboard
＊Temporary FRP switchboard