Telephone Wiring Circuits

Reprinted from "INSULATORS - Crown Jewels of the Wire", July 1974, page 31

Dear Dora,

I have a question about an insulator that I got recently, and information about the use of Phantom Circuits for open wire phone lines.

First: I got a McLaughlin 20 CD 164 that is quite different from any other McLaughlin 20 that I've seen. It is embossed as follows: F. MCLAUCHLIN (large, heavy letters "C" instead of "G"); B. NO - 20 (large, heavy letters and numbers). Also the drip points are large, round, and spaced very close together. Have you ever seen or heard of anything like it before?

The following diagrams on Phantom Circuits were taken from The U.S. Army Lineman's Handbook.

This is a typical telephone and wiring. The next three diagrams will show the ways to use one or more pairs of wires to obtain more than one line on each pair. All three of these circuits require devices called repeating coils. They are used to "split" the pair or pairs of phone wires so that the additional circuit may be added. The first is the Simplex Circuit. It is used to obtain two talking circuits from one phone line.

This circuit operates as Follows: Phone A uses both wires to transmit and receive; phone B uses one wire and the earth to transmit and receive.

The second is the Phantom Circuit. It is used to get three talking circuits from two phone lines.

This circuit operates as follows: Phones A and C use both wires to transmit and receive; phone B uses one wire from each pair to transmit and receive.

The third is the Simplex-Phantom Circuit. It is used to get four talking circuits from two phone lines.

This circuit operates as follows: Phones A and D use both wires to transmit and receive; phone C uses one wire from each pair to transmit and receive; phone B uses one wire from one pair and the earth to transmit and receive.

These circuits were used in the late 1890's up to the early 1900's. They were eliminated because of problems associated with balancing the resistance of each line. Today the only organization that I know of that uses these circuits is the U.S. Army, and they are phasing them out slowly.

I hope that this information and these diagrams will help answer questions that readers have about this part of insulators. 
Sincerely yours, 
Jim Decker 
460 Division St., Apt 7
Pleasanton, CA 94566

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Thank you, Jim, for the info on Phantom Circuits. Regarding your question concerning the McLaughlin No. 20 insulator, I am not familiar with this one, but perhaps some of our McLaughlin specialists can help.