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The Development of Wire Gages - Radio World

The Development of Wire Gages

Where did the idea of wire sizes come from? Even ancient wire came in various sizes, and there are dozens of systems, many still in use. As late as the 1800s, there were no useful standards.
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Come gather 'round as Grandpa Lampen continues his story about wire and cable.

Where did the idea of wire sizes come from? Even ancient wire came in various sizes, and there are dozens of systems, many still in use. As late as the 1800s, there were no useful standards.

In 1856, clockmakers Joseph R. Brown and apprentice-turned-partner Lucian Sharpe had begun to manufacture precision measuring tools in Pawtucket, R.I. One that was sorely needed was an accurate measuring gage for wire. (Readers will note that I prefer the spelling gage, commonly accepted in reference to wire, and accepted as a variant for gauge by the American Heritage Dictionary.)

Sharpe suggested producing sizes of wire in a regular geometric progression. Until that time, wire-measuring tools were made by English manufacturers and were, to say the least, variable in quality and accuracy. Sharpe took 50 of his new low-cost gages to a meeting of brass manufacturers of Connecticut, centered in the Naugatuck Valley. A gage consisted of a flat circular piece of steel with precision-machined slots corresponding to the different sizes of wire.

It was a big hit. Brown & Sharpe wire gages became the standard well into the 20th century. Eventually, Sharpe's progressive system became adopted as the AWG, or American Wire Gage, which we use today.

One world, one gage

If you look at a wire gage table, as shown in Table 1, you can see the relationship.

For example, Sharpe defined 36 AWG as 5 mil, or 5/1000ths of an inch or 0.005 inches, in diameter, and 0000 AWG, called "4-aught," as 0.460 inches. These diameters are calculated values related to the area of the wire, more precisely called the "circular mil area" or CMA. The progression of gage sizes is a simple mathematic progression of the circular mil area, up or down.

Gages for stranded wire are different than those for solid. Stranded wire, after all, has spaces between strands. The size of a stranded wire is larger for the same resistance as a solid wire. Otherwise, the same formulas of area and gage apply.

Why did Sharpe choose to have his gage numbers get smaller as the wire got bigger? He was trying to describe the performance - i.e., the resistance - of the wire, which goes down as the wire gets bigger. So 18 AWG is lower resistance than 19 AWG, as the numbers indicate.

Those using wire could now get the size and performance they were paying for, and the consistency and repeatability no matter who made the wire.

Picking up the phone

The longest wires made to that time were the transatlantic telegraph cables mentioned in an earlier article. But Lord Kelvin, who had been instrumental in the laying of the cable, later said the telephone, rather than the telegraph, was "the most wonderful thing I have seen in America."

The world was ready for an electrical speech machine, as Alexander Bell called it. It was invented on February 14, 1876, in Boston.

Or was it?

In 1854 a Frenchman, Charles Bourseul (1829-1912) suggested transmitting speech electrically. He said, "Speak against one diaphragm and let each vibration make or break the electric contact. The electric pulsations thereby produced will set the other diaphragm working, and (we hear) the transmitted sound."




By 1860 a German, Philip Reis, a 26-year-old science teacher, was working on a design in which a paper diaphragm moved an iron needle inside a coil, producing a change in inductance in response to sound. These telephones went into production but the quality varied widely, and some did not work at all.

On Jan. 20, 1874, German inventor Ernst W. Siemens patented a moving-coil transducer. His U.S. patent application described a "magneto-electric apparatus" that could transmit "the mechanical movement of an electrical coil from electrical currents transmitted through it." However, this eventually turned into the first moving-coil loudspeaker. Its use as a microphone was never explored.

Bell (1847-1922) was intending to build something to allow the deaf to hear. Both his father and grandfather had taught the deaf. His version moved a needle in an acid solution, varying the resistance. It worked; but the use of liquids, which move and evaporate, was equally impractical.

On Feb. 14, 1876, Bell submitted his patent for the telephone. Only four hours later, Elisha Gray, also a prolific inventor, submitted his version of the same device.

In retrospect, it is doubtful whether either of these submissions actually worked. However, when Bell's device did work, three days later, it contained some new items. Some say, to this day, that the additions, such as varying the resistance in an acid solution, were amazingly similar to some of the disclosures in Gray's patent application.

A new era begins

While Elisha may have been robbed of his rightful place in history, don't feel too sorry for him.

In 1869, he and his partner Enos Barton started a company called Gray and Barton, manufacturing and distributing telegraph and telephone equipment in Cleveland. Three years later, they moved the company to Chicago and renamed it the Western Electric Manufacturing Company. The Bell System purchased Western Electric in 1881 and made it into the largest electrical manufacturer in the world.

Later, Western Electric was broken up. One of the resulting companies was named for Elisha Gray and Enos Barton, with the union of their names, Graybar, which you may recognize as a major distributor of electronic parts.

Ah, but we have barely begun the story of the telephone and of the twisted pair of wires that supported it. Stay tuned for the next exciting episode.

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