New Cable Conquers Congestion (Sep, 1939)
New Cable Conquers Congestion
IMAGINE a city street with a thousand rows of telephone poles, each holding aloft sixty wires!
Of course such a street would look more like a bad dream than any kind of a thoroughfare, but without the modern lead-covered cable that’s exactly what half the streets in most of our larger cities would look like. The picture at the left showing lower Broadway, in New York City, in the ’80s gives a slight hint of what a city street would look like without present day cables, developed in the past four decades by telephone engineers.
The latest development in lead-covered telephone cables has recently been made by engineers of the Bell system with the manufacture of a cable containing 4,242 separately insulated copper wires. Before this, the maximum contained in one cable has been 3,636 wires. Despite the increase in the number of wires contained, the new cable is not a fraction of an inch larger than its predecessor.
Since the diameter of each wire in the new cable is also the same as before, the feat of placing 606 more within the same girth was made possible by an improved technique of wire insulation, a method which reduced the thickness of insulation around each strand.
The decrease in each case was one 3/1000 of an inch but this tiny saving, repeated 3,636 times, resulted in a total saving of space sufficient to afford room for additional wires. The method of insulating wires is in itself a revolutionary development of the last decade. Previous to the invention of this process, wires intended for cable had been insulated by wrapping paper ribbon spirally around them. Then it was discovered that paper pulp could be formed around the wire, and now giant machines literally manufacture a thin coating of paper right on the wire, 60 strands at once, as they path through a bath of pulp.
The cable core of 4,242 conductors is built up from these individual strands by first twisting two wires into a pair, then binding 101 of these pairs into a unit. Finally 21 of these units are twisted together, and the core, after being dried out in vacuum ovens, is sheathed with lead that is forced through dies under great pressure.
Perhaps the greatest contrast between the old and new methods of cable manufacture is to be found in the manner of applying the lead sheath. The antecedents of the swift and sure lead presses of today were ex-sailors. To the accompaniment of their chanted “Heave Ho,” the core was actually pulled through lengths of lead pipe by hand. Plumbers were then called in to “wipe the joints” and make one continuous lead pipe out of various sections. Lead presses made this procedure obsolete shortly before 1900.
Just what such advances in cable manufacture mean can best be understood when we realize that it would require seventy rows of telephone poles, each holding sixty wires, to carry the wires contained in just one of the new cables. Under one street corner in New York City today there are 282 cables, containing 560,000 wires!
The work of cable development has had a profound effect on modern life which is difficult to appraise, but it is safe to say that without the modern cable, embracing its tightly packed wire?, the modern city as we know it could never have been.