SPRING JACK PLUG BOARDS
These Plug boards are made both for Single and Double Lines and can be used for a variety of purposes.
If. used with a domestic or other type of indicator they, can be connected so that when the operator's plug is inserted the indicator is disconnected and the operator's telephone connected as in ordinary telephone switchboards. This is particularly useful in ordinary domestic telephone installations. They can also be used for intercepting telephone lines on an Exchange. It is sometimes necessary for a principal in a firm to be able to call up any telephone without first calling the Exchange. The lines are first brought to one of the above plug boards and then continued to the Exchange; when the plug is inserted the line to the Exchange is entirely disconnected, and the principal is then connected direct to the person with whom he requires conversation.
Taken from the G.E.C. Illustrated Telephone Catalogue 9th edition (1904)
Last revised: January 27, 2011