History of Inductive Coordination

The early telephone sets were operated over grounded lines, and interference between telephone and telegraph lines, and between the telephone circuits themselves, was immediately experienced. Power systems and electric railways were introduced during this same period; and, especially after alternating current came into use, much interference resulted.

The history of interference is interesting^15,16 as the following quotation indicates.

About 1883 a new iron wire was made which, it was claimed, would be free from inductive disturbances. Its cross-section was shaped like a four-leaf clover and the grooves ran around the wire in a spiral. The company that was making and promoting this wire interested themselves in its use on more than a dozen experimental lines. They had a theory that the voice current would follow the spiral and in some way produce a beneficial effect. An officer of the spiral wire company said it was not understood by electricians.⁽¹⁾

The use of two-wire, or metallic, instead of grounded telephone circuits did much to reduce noise. They were introduced commercially by Carty.¹⁰ Disturbances were further reduced by transpositions explained by Carty in his paper¹⁷ presented in 1891.

The process by which electric energy is transferred from one circuit to another, causing noise or other disturbances in low-level communication circuits, is termed induction. The interference caused thereby is called inductive interference. The transfer of energy may be largely through the effect of the electric field or the magnetic field, or by both. Power engineers and communication engineers cooperate in minimizing these effects, such activities leading to inductive coordination.

Perhaps the earliest comprehensive cooperative survey was begun in 1912. Rules were formulated and published¹⁸ for the coordination of power and telephone systems so that inductive disturbances would be minimum. After 1921, coordination activities were centered in a joint general committee of the National Electric Light Association and the Bell Telephone System.¹⁹ More recently, committees of the Edison Electric Institute and the Bell System have continued this work. Excellent cooperation exists between the power and communication organizations, and inductive interference has been rendered controllable.

(1)	Reprinted by permission from Beginnings of Telephony by F. L. Rhodes, Harper & Bros.