Open Wire Construction & Maintenance Tools
The 5A Type Switch Box For Transposing Working Open Wire Circuits
The use of transpositions in open wire lines, whether by side brackets or by juxtaposition of pins and steel brackets on crossarm leads, is necessary to prevent crosstalk. Crosstalk is caused by mutual coupling on wire pairs and is prevented by the careful application of interchanging the wires of a pair in a pre-determined pattern from Central Office (C. O.) to C. O. or customer in the local loop.
Most transpositioning is done while the lines are being constructed and it is best, as the art of making transpositions in working open wire circuits with lots of traffic, makes it tenuous at best. However, sometimes due to a traffic accident, a flood, a sleet or ice storm, or other reason, it was necessary to cut in open wire transpositions when the wires were energized.
By choice, commercial telephone companies would justify cutting in transpositions or “tramp brackets” as linemen would call them, during times of lightest telephone traffic. While some wires were cut “dead,” that is during sleet repairs and such times, it was often the case wires could not be taken out of service and thus, certain methods were followed.
Lines for D. C. telegraph, composite telegraph and voice channel communications were handled differently during this process. Our purpose here is to explain the nature of transposing voice channel working circuits which were either physical or phantomed (non-physically connected) circuits.
The use of two devices, one the older “Dial Type 12039 Switch Box,” and the newer (c. 1933) “Type 5A,” is the topic of our discussion today. While altering an existing phantom transposition did not interrupt simplex d.c. telegraph–or affect them negatively, physically cutting in (or out) to a side circuit for a transposition, did affect them. The Central Office became involved in this process, too, when the 5A Box was used on swapping side circuits. During those times, the C. O. utilized the Phantom Switching Relay for continuity.
When older open wire was restrung, rehabilitated or re-constructed for high grade voice frequency circuits, the newer Type 5A box was preferred.
Let’s discuss cutting in a transposition using the newer Type 5A Switch Box. What did it look like? How was it used? And finally, how did it work?
“Throwing a Phantom . . .”