History of Thomas Edison's DC electrical cables & wiring.

Photos, patent history, description of solid metal electrical cables designed by Thomas Edison and originally installed underground in New York.

Page top photo: one of the connectors used to joint Edison's solid metal electrical cables buried underground and used to conduct DC electrical power in New York City.

In this article series we list common old building electrical wiring system safety concerns and we illustrate types of old electrical wires and devices.

Thomas Edison's Early DC Electrical Cables

"So much has been said and written upon the subject of high-tension electric currents and their probable or possible danger to human life, and so many different opinions have been advanced by men whose positions serve to surround their utterances with an atmosphere of knowledge of the matter under discussion, that the mind of an unscientific public has been unable to come to any definite conclusion upon the basis of "expert" testimony.

... With the increase of electric lighting (which today is used only to a very limited extent as compared with its inevitable future use) and the multiplication of wires, these dangers which exist now in a thousand different parts of the city will be manifolded many times."

- Thomas A. Edison, THE DANGERS of ELECTRIC LIGHTING [PDF] The North American Review, 149(396), pp.625-634.1889

These rusty looking "pipes" may be the last known remnants of the oldest and original electrical wiring used for underground electrical power distribution in the U.S.

They were last seen leaning against the wall in a back corridor of the steam boiler room at the Pratt Institute in New York City.

We describe these electrical power cables and provide images of and links to early electrical wiring and wire insulation methods in this article series.

[Click to enlarge any image]

In the electrical wire history & old wire identification article below we illustrate a variety of types of electrical wiring found in older buildings based on the wire insulation material (asbestos, cloth, plastic, metal) and the wire material itself: copper, aluminum, copper-clad aluminum, tinned copper.

Edison's Solid Iron Tubing or Steel Pipe & Pitch Insulated Electrical Cables

Below: a snippet (ok really a hack sawn chunk) of New York history: these are original Edison DC electrical power cables from beneath a New York City Street.

At STEAM BOILERS GENERATORS CONTROLS, PRATT we explain that the Pratt steam room engineer and himself a collector and historian, Conrad Milster spotted these "pipes" while looking into a utility trench where Con Ed was doing some other work in New York.

Milster salvaged a number of Edison's conduit sections and connectors and was generous enough to share them and describe them to the author who visited Milster shortly prior to his retirement from the Pratt Institute.

Thomas Edison's Earliest Electrical Cables for DC Electrical Service

He obtained sample segments of both the DC electrical system distribution cabling and the connecting joints that were used between these "wires" to permit lateral connections to buildings. Edison referred to these early electrical conductors as "iron tubing".

Above we're looking at the cut-end of what is most likely a section of original DC or continuous current distribution cabling salvaged from a NYC trench.

The solid copper core is much thicker than my thumb. It's Conrad's eye of an engineer that is turned towards history that enabled him to spot and salvage this interesting relic that otherwise would certainly have been buried in a landfill.

The solid copper core was wrapped in rope to insulate it from the iron pipe and the space between that cable and the surrounding iron pipe was filled with a pitch-like substance. - C.M.

Ends of 20-foot long pipes terminated in cast-iron boxes where they were connected with soldered jumpers. - C.M. The electrical cable junction box that permitted both joining of the otherwise pipe-encased electrical power distribution cables and perhaps the tapping off to bring electrical power into nearby buildings.

In 1889 Edison described four classes of electrical current in use.

1. Low-tension continuous current, with a pressure not exceeding 200 volts, used for incandescent lighting.
2. High-tension continuous current, with a pressure of 2,000 volts and over
3. High-tension semi-continuous current, with a pressure of 2,000 volts and over
4. Alternating current, with a pressure from 1,000 to 3,000 volts and over.

"Continuous current" as used by Edison refers to what in 2016 is called "DC" or "direct current" and his "alternating current" describes what is more widely used today as "AC".

Edison, a believer in DC as safer than AC, explained that at lower voltages ("pressures") DC current at low voltages. Edison understood very well the role of electrical wire insulation and the forces that affected the safety of electrical wiring systems, writing:

The first is harmless, and can be passed through the human body without producing uncomfortable sensations. The second is dangerous to life. Momentary contact with a conductor of the third results in paralysis or death, as has frequently occurred; and the passage of the fourth, or alternating, [sic] current through any living body means instantaneous death.

These are simple facts which cannot be disproved. There is a record of nearly one hundred deaths, which furnishes an unanswerable argument in support of these statements. Discussion and controversy may serve the questionable purpose of delaying popular faith in them, but they cannot change them; ...

It has often been asked why the number of accidents of this nature is larger in the city of New York than any other city. The reason is that New York has a greater number of wires to the square mile than any other city in the united states. ...

... the popular cry seems to be "Put the wires underground." BUt, instead of diminishing, this will increase the danger to life and property.

There is no known insulation which will confine these high-tension currents for more than a limited period, and when they are placed beneath the ground, with the present system of conduits, the result will be a series of earth-contacts, the fusion of wires, and the formation of powerful electric arcs, which will extend to other metallic conductors in the same conduit , and a whole mass of wires made to receive this dangerous current and convey it into houses, offices, stores, etc.

Near the corner of William and Wall Streets, New York, the underground conductors of the Edison Illuminating Company became crossed, and the current which was passing through them at a pressure of only one hundred and ten volts melted not only the wires, but several feet of iron tubing in which they were incased, and reduced the paving-stones within a radius of three or four feet to a molten mass.This system is so arranged that consumers are not affected by such accidents as this.

They may and do mean expense to the company, but the public are entirely free from any possibility of danger.

... So long as the insulation retains its original elasticity, the current is confined; but the influence of the air, or of gas and other agents, tends to change the elasticity, and the billions of vibrations to which it has been subjected finally render it very susceptible of being pierced by a spark of static electricity.

Thus an avenue for the ingress of moisture is formed, not only in one spot, but in many, through which the current may be communicated to any conductor of electricity near enough to make physical contact, or a circuit may be completed between the two by a line of moisture or the formation of an electric arc, with its subsequent destructive action.

... There is no plea which will justify the use of high-tension and alternating currents, either in a scientific or a commercial sense.

They are employed solely to reduce investment in copper wire and real estate. ... The alternating current under high pressure and direct-current under high-pressure systems are also employed, as I have intimated, to save investment in real estate as well as copper.
- (Edison 1889)

• Edison, T.A., THE DANGERS of ELECTRIC LIGHTING [PDF] The North American Review, 149(396), pp.625-634.1889 RE-published by the University of Northern Iowa, http://www.jstor.org/stable/25101896 and available on JSTOR.

Research, History, Thomas Edison's Patents on Electrical Wiring

• Dini, David A., P.E., SOME HISTORY OF RESIDENTIAL WIRING PRACTICES IN THE U.S. [PDF] Underwriters Laboratories, Inc., (2006)
• Dini, David A., Thomas Z. Fabian, and J. Thomas Chapin. AN ANALYTICAL STUDY OF SOME PHYSICAL PROPERTIES OF WIRE AND CABLE SAMPLES COLLECTED FROM OLDER HOMES [PDF] Underwriters Laboratories Inc (2006). David Dini, Northbrook, Ill. Tel: 1.847.664.2982; Email: David.A.Dini@us.ul.com
  
  These two papers were presented at the FPRF Aged Electrical Systems Symposium of 2006. These papers on this subject can be downloaded for free.
  http://www.nfpa.org/research/fire-protection-research-foundation/projects-reports-and-proceedings/proceedings/2006-proceedings/aged-electrical-systems-symposium
• Edison, T.A., THE DANGERS of ELECTRIC LIGHTING [PDF] The North American Review, 149(396), pp.625-634.1889 RE-published by the University of Northern Iowa, http://www.jstor.org/stable/25101896 and available on JSTOR.
• Edison, Thomas A. "Manufacture of filaments for incandescent electric lamps." U.S. Patent 470,925, issued March 15, 1892.
  Abstract:
  
  As before explained in prior applications for patents for inventions of mine relating to lighting by electricity, it is essential that the incandescing conductor should be of high resistance and that great advantages result from the increase of resistance when such increase can be obtained without increase in the extent of the radiating surface.
  
  I have discovered that an incandescing conductor of very high resistance in comparison with the radiating surface may be made by taking several exceedingly-fine fibers or filaments of carbonizable material and welding them together prior to carbonization by a suitable cementing carbonizable liquid.
  
  For this purpose I prefer to use natural fiberssuc'h as bast, jute, manila, hemp, &c.-or other fibers of endogenous growth made up of a great number of parallel elementaryfibers cemented together by a natural cementing material, which on carbonization locks all the elementary fibers together into a homogeneous filament.
  
  I take several of these natural fibers, and after removing the extraneous matter by passing them through a cutting-die I form them into a bunch and dip them together into a solution of sugar or other carbonizable liquid and then carbonize them as one fiber, the carbonizable cementing-liquid binding them firmly together into a homogeneous filament of high resistance and moderate radiating surface.

• Edison, Thomas A. ELECTRIC CONDUCTOR [PDF] U.S. Patent 470,924, issued March 15, 1892.
  Excerpt:
  
  The main feature of the invention is the use as an insulating-covering of a mixture of rubber with an infusible material in the form of a powder.
  
  
• Edison, Thomas A. ELECTRICAL INDICATOR [PDF] U.S. Patent 307,031, issued October 21, 1884.
  Abstract:
  
  The object of my invention is to produce an eflicient apparatus for indicating variations of electro-inotive force in an electric circuit, preferably for use in connection with systems of electrical distribution to show the changes in pressure in the various parts of the district.
  
  The apparatus is also capable of use in automatically regulating the elcctro-motive force to correspond with such variations.
  
  I have discovered that if a conducting substance is interposed anywhere in the vacuous space within the globe of an incandescent electric lamp, and said conducting substance is connected outside of the lamp with one terminal, preferably the positive one,of the incandescent conductor, a portion of the current will,when the lamp is in operation, pass through the shunt-circuit thus formed, which shunt includes a portion of the vacuous space within the lamp.
  
  This current I have found to be proportional to the degree of incandescence of the conductor or candle-power of the lamp.
• Edison, Thomas Alva. ELECTRIC LAMP [PDF] U.S. Patent 223,898, issued January 27, 1880. (also listed as 1879)
  Abstract: filled with scanning typographical errors -hard to read. Excerpt:
  
  By using the carbon wire of such high resistance l mu enabled to use flnc platinum wires for leiuling'wires, as they will have a small resistance compared to the burner, and hence will not limit and crack the sealed vac uunl-bulb. llatinu can only be used. no its expansion is nearly the same as that of glass.
  
  By using a considerable length of carbon wire and coiling it the exterior, which Is only a small portion of its entire surface, will form the principal rndiuting-surtnce;
  
  hence I am able to raise the apccitic heat of the whole of the carbon, and thus prevent the rapid reception and disuppeamncc of the light, which on a plain wire is pn-judicial, as it shows the least. unsteadiness of the current by the flickering of the light; but it the current is steady the defect does not show.
  
  I have carbonized and used cotton and linen thread, wood splints, papers coiled in various ways, also lamp-black, plunibago, and carbon in various forms, mixed with tar and kneaded so that the same may be rolled out into wires of various lengths and diameters.
  
  Each wire. however, is to be uniform in size throughout.
• Greenfield, Edwin T. ARMORED ELECTRIC CABLE U.S. Patent 616,612, issued December 27, 1898. Filed 1986
  Excerpt:
  
  Be it known that I, EDWIN T. GREENFIELD, a citizen of the United States, residing at New York, in the county of New York and State of New York, have made a new and useful Invention in Armored Electric Cables, of which the following is a specification.
  
  My invention is directed particularly to improvements in electric cables designed for ocean service, and has for its objects,
  
  first, to devise an armored cable of such anature that the insulation of the cable will be thoroughly protected from the attacks of borers or other insects or animals which usually attack cables of this nature when sunk in the body of the ocean
  
  second, to devise an armored cable of such a nature that its exterior armor will fully protect it (the cable) from unnatural wear when it is suspended over ledges of rock in the body of the ocean;
  
  third, to provide a cable of the nature indicated in which the armor is of steel, phosphor-bronze, or any preferred metal having the desired strength and qualities for adapting it for use in the ocean and in making such armor of a flexible nature, so that the completed cable may be wound upon a drum in the usual way when it is desired to lay it in the bed of the ocean, and,
  
  fourth, to provide a lead or equivalent covered cable with a flexible protecting armor which will protect the lead covering from the action of metal slivers when drawn into a conduit.
• Hargadon, Andrew B., and Yellowlees Douglas. "When innovations meet institutions: Edison and the design of the electric light." Administrative science quarterly 46, no. 3 (2001): 476-501.
  Abstract:
  
  This paper considers the role of design, as the emergent arrangement of concrete details that embodies a new idea, in mediating between innovations and established institutional fields as entrepreneurs attempt to introduce change.
  
  Analysis of Thomas Edison's system of electric lighting offers insights into how the grounded details of an innovation's design shape its acceptance and ultimate impact. The notion of robust design is introduced to explain how Edison's design strategy enabled his organization to gain acceptance for an innovation that would ultimately displace the existing institutions of the gas industry.
  
  By examining the principles through which design allows entrepreneurs to exploit the established institutions while simultaneously retaining the flexibility to displace them, this analysis highlights the value of robust design strategies in innovation efforts, including the phonograph, the online service provider, and the digital video recorder.
• Hughes, Thomas P. "The electrification of America: the system builders." Technology and Culture 20, no. 1 (1979): 124-161.
• Hughes, Thomas Parke. "British electrical industry lag: 1882-1888." Technology and Culture 3, no. 1 (1962): 27-44.
• Norwig, E. A. "Patents of Thomas A. Edison, The." J. Pat. Off. Soc'y 36 (1954): 275.
• Shaver, Lea. "Illuminating innovation: From patent racing to patent war." Wash. & Lee L. Rev. 69 (2012): 1891.

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