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Knob and tube wiring with illegal extension (C) Daniel FriedmanOld Electrical Wiring Types, History of Electrical Wire Types
Photo guide to types of Electrical Wiring in Older buildings

  • OLD ELECTRICAL WIRING TYPES - CONTENTS :History of electrical wire & electrical wiring: how to recognize knob and tube electrical wiring and unsafe "extension cord" wiring. How to evaluate the number of electrical circuits in an older home. Photo guide to types of old building electrical wires.
  • POST a QUESTION or READ FAQs about old house wiring, knob & tube, old fuse panels, old house wiring condition & safety
  • REFERENCES
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Photos help identify types, condition, & hazards of old electrical wiring in buildings.

In this article series we list common old building electrical wiring system safety concerns and we illustrate types of old electrical wires and devices. This article series answers basic questions about assessing and repairing the electrical service, capacity, wiring type, condition, and safety in older homes.



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Photo Guide to Old Electrical Wire Types

Original DC electrical wires from beneath New York City Streets  (C) Daniel Friedman"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 remnants of the oldest and original electrical wiring used for underground electrical power distribution in the U.S. We describe these electrical power cables and provide images of and links to early electrical wiring and wire insulation methods in this article.

[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. While varying somewhat by area of the country in the U.S., Latin America, Europe, and other areas, there are recognizable generations of electrical wiring ( KNOB & TUBE, greenfield, armored cable or " BX" wiring, plastic or " NM/NMC" wiring), wiring materials (copper, tinned copper, aluminum, copper-plated aluminum).

Proper identification of the type of electrical wire and wire insulation is useful for those seeking to guess at the age of a building or of its electrical system, and in some instances it is helpful in assessing the condition and safety of the building wiring system, such as taking note of the presence of branch circuit solid conductor aluminum electrical wire that has not been properly repaired - a fire hazard.

Article Contents

A 1980 US CPSC study found that aging electrical systems are a factor in the occurrence of electrical fires in homes, an observation confirmed separately by Aronstein in explaining aluminum wiring hazards in what Aronstein calls the "bathtub curve" that maps failure rates over time. Failures occur early in the wiring system life due to original installation defects and then failures occur again at an increased rate late in the installation's life as the wiring ages and as it has been exposed to the vagaries of use over decades.

But Dini points out that "... most of the hazardous conditions found in the 30 houses [studied] could be attributed to a lack of compliance with a specific code requirement". (Dini 2008).

Braided fabric vs plastic wire insulation (C) Daniel Friedman

Above: two types of branch circuit electrical wire insulation are shown in our photo: braided fabric wire insulation, probably cotton covered with wax or varnish, and newer plastic wire insulation. The braided fabric wire insulation was found on a 1960's fluorescent light ballast, while the plastic wire was used in the branch circuit wiring for the light where that ballast was employed. The old style ballast and its wire could have dated from the 1950's.

Aluminum Electrical Wiring Types

Stripped aluminum wire (C) Daniel Friedman

[Click to enlarge any image]

As you see in the photo above, typically aluminum electrical branch circuit wiring was plastic-covered. Aluminum wiring has been studied since about 1945, and began appearing in homes in North American as early as 1965. In that year Kaiser Aluminum and Chemical Corporation (KACC) began marketing KA-Flex solid-conductor aluminum wiring. Unless it has been properly repaired or replaced, aluminum wiring in homes or other buildings is a serious fire hazard.

See ALUMINUM WIRING IDENTIFICATION

Or see ALUMINUM WIRING GUIDE for HOME INSPECTORS for a discussion of safety hazards associated with aluminum wiring.

Watch out: improper "repair" of aluminum wiring using connectors that do not successfully prevent overheating (CO/ALR, CU-AL-stamped devices, and the Ideal No. 65 purple Twister), may increase the fire hazard in a home and worse, may lead occupants to ignore danger signs of a possible fire, thinking that their wiring is now repaired and safe.

Armored Cable Electrical Wiring "BX" & "Greenfield" - Metallic Sheathed Electrical Wire

Two generations of metallic sheathed or armored cable wiring (C) Daniel Friedman

The photo above illustrates two generations of metallic-sheathed armored cable or "BX" electrical wire.

The larger diameter wider-wrapped armored cable is probably Greenfield flexible steel armored cable, a wiring type patented in 1898.

Where does "BX" come from? Dini (2006) explains that this cable was produced by Greenfield, one of its inventors, in two experimental forms AX and BX (X = experimental). The second version "B" was the more successful version that was produced.

The term "BX" stuck on later versions of flexible metal armored cable: the smaller-diameter modern "BX" wire is in the left of the photo and connects to the left side of the electrical box.

Also see ELECTRICAL WIRE STRIPPING TIPS where we discuss stripping and working with BX or armored cable.

Greenfield's original design used multiple strands of copper conductors, typically twisted, and surrounded by a pitch-like insulating material like that we illustrate in Edison's original underground electrical cables shown at STEAM BOILERS GENERATORS CONTROLS, PRATT.

Here are the original image and a text excerpt from Edwin T. Greenfield's 1898 patent:

Greenfield patent No. US 616612 in 1898 - U.S. Patent Office

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 nature 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.

Also see a brother wiring material sold without conductors: CONDUIT WIRE IDENTIFICATION in this article.

Asbestos-Insulated Electrical Wiring

Installation of quinterra wrapped coils in an elctrical motor - asbestos electrical insulation - Rosato (C) InspectApedia

The asbestos-insulated electrical wiring wire loom or "flexible conduit" shown above is discussed in detail at ASBESTOS ELECTRICAL INSULATION. More examples of non-asbestos wire loom are given later in this article.

Cloth & Varnished-Cloth Insulated Electrical Wiring

Varnished cloth insulated electrical wire (C) Daniel Friedman

[Click to enlarge any image]

Cloth, fabric insulated wire may also be labelled "plastic" wire and will contain conductors whose individual insulation may be made of rubber, asbestos-containing rubber, or plastic (in later wires). Above and just below: varnished-cloth electrical wire on the ballast used in a fluorescent light fixture in a 1960's home built in northern Minnesota.

Cloth electrical wire insulation, possibly asbestos-impregnated (C) Daniel Friedman

Watch out: by visual inspection I don't think we can distinguish cloth, non-asbestos wiring insulation of this age from Type AVB, A plain [flame?] -retardant cotton braid: an insulation consisting of varnished cloth and impregnated asbestos. Asbestos-impregnated type AVB cloth wiring insulation is discussed separately at ASBESTOS ELECTRICAL INSULATION.

However as you see in my photo below, this old cloth-covered electrical wire is charred in two places, making me think it may not contain asbestos. However no tests were performed.

Charring on cloth wire insulation suggests not asbestos but this wire has not yet been tested for asbestos content (C) DanieL Friedman

Power Cable for Electric Welder

Electrical wire for a welding unit (C) InspectApedia.com EG

The damaged power cable shown above was used with a 1970's electric welder. Beneath the heavy rubber exterior of the welder power cable we see a cloth fabric that might be an asbestos fabric needed for extra heat resistance. Other readers familiar with this welder cable are invited to use the page top or bottom CONTACT link to offer more information.

Conduit for Electrical Wiring

Metal and more recently plastic tubing are both used as conduit for routing and protecting electrical wiring in a wide range of applications. Dini (2006) notes that the earliest wire conduit material (ca 1910) was made of wood moldings grooved to carry the conductors and covered with a wooden cap.

But you won't find that material today except perhaps in an authentic or un-restored older building. Modern conduit is made of rigid metal that can be bent into elbows, plastic that includes pre-bent elbows, and flexible metal and plastic ENT materials. Below you will notice large diameter plastic conduit bringing power to an electrical sub panel.

Electrical conduit mistakes (C) D Friedman T Hemm

Electrical conduit is also sold in a flexible metal design that should not be confused with BX or Greenfield armored cable: this flexible metal conduit looks like BX or armored cable but is sold "empty". Below this section of flexible metal conduit was a left-over scrap that had had three wires inserted through the protective cable.

Armored cable, 12/3  Armorlite BX wire (C) Daniel Friedman

To compare flexible conduit with armored cable, BX, or Greenfield wiring, see ARMORED CABLE or BX WIRE IDENTIFICATION in this article.

Flexible electrical conduit pre-wired whip for outdoor use (C) D Friedman

In nearly all new outdoor air conditioner & heat pump installations the electrician uses a pre-wired waterproof electrical conduit whip (photo above).

For more details please see our separate article ELECTRICAL CONDUITwhere we describe just about all of the types of modern electrical conduit materials including some not shown above.

Copper-Clad Aluminum Electrical Wiring

Copper-clad aluminum electrical wiring markings (C) InspectApedia Roger Hankey

[Click to enlarge any image]

The photograph of copper-clad aluminum electrical wire shows the wiring sheathing markings [click to enlarge]. This NMC or non-metallic-sheathed cable electrical wire was observed in a 1974 Edina MN townhouse and was connected to an FPE electrical panel.

Unlike aluminum electrical wire used in branch circuits (a fire hazard), copper-clad aluminum wire performs about as well as copper wire and is considered safe for use in homes provided of course that the wiring has been correctly installed. Photograph above provided by and used with permission of Roger Hankey, a Minnesota home inspector.

See details about copper-clad aluminum electrical wiring at COPPER-CLAD ALUMINUM ELECTRICAL WIRE

Copper clad aluminum wire (C) Daniel Friedman

Extension Cord Electrical Wiring

As we cited earlier at NUMBER of CIRCUITS in OLD BUILDINGS, use of zip cord or extension cord mounted on or through walls and ceilings to add lighting circuits or receptacles is improper, unsafe (a fire hazard), and is often an indication that the building does not have enough circuits for modern usage.

Extension cord or zip cord wiring used to add a light fixture (C) Daniel Friedman

Watch out: where we find zip cord electrical wiring it is important to see what other unsafe wiring practices that same installer may have followed.

Extension cord wiring is unsafe (C) Daniel Friedman

Above the same do-it-yourself' er has left at least six, probably more unsafe details at this electrical receptacle:

  1. Missing strain relief on armored cable
  2. Extension cord wiring used to extend the circuit
  3. Second circuit (below the armored cable) stripped back without connection to the electrical box at all
  4. Electrical box too small for number of conductors
  5. Electrical box inadequately secured to the building
  6. No cover plate on the electrical box.

Below we show the front of this add-on electrical receptacle. One thing is "correct" though: the installer used a two-prong receptacle that excludes a third ground prong opening - as he should have done as the circuit does not include a grounding conductor.

Unsafe electrical receptacle (C) Daniel Friedman

Fabric Covered NMC Electrical Wire Insulation

Fabric covered electrical conductors in an electrical panel (C) Daniel Friedman\ Silver colored fabric insulated electrical wire (C) Daniel Friedman

Above is a common silver-colored fabric-insulated electrical cable wire.

[Click to enlarge any image]

But fabric-covered wiring may be found in other colors including white, black, brown.

Aluminum NMC wire (C) Daniel Friedman

The exterior insulation on fabric-insulated NMC electrical wires are often black, silver, or white. The individual wires within the cable may be insulated in rubber or fabric-covered rubber or they may be insulated by plastic in later wiring products. Below we illustrate the fragile properties of older fabric covered wire insulation .

Above is white plastic-coated fabric-insulated electrical wire. This early NMC or nonmetallic sheathed cable is probably a later design using rayon, but earlier NMC was wrapped in a cotton braid sealed with varnish (white or tan cables) or a tar-lie substance (the cabling we show below). (Dini 2006).

Fragile insulation on older electrical wire (C) Daniel Friedman

Inside this silver painted fabric-jacketed electrical wire you can see that the individual conductors were insulated in by a plastic coating.

Watch out: as our photos illustrate, the insulation on older fabric or rubber insulated wires may be fragile. In stripping wires for splicing or connection you may get into a messy too-short wire problem if you don't work carefully. Worse, deteriorated insulation on electrical wires may indicate a history of overheating and such circuits may be unsafe.

Fabric, paper, and plastic insulated electrical wire being stripped (C) Daniel Friedman

Above and below I'm stripping an older type of fabric-insulated electrical cable in a Haddonfield New Jersey home. You can see that inside the wire jacket these conductors were insulated by rubber.

Black fabric insulated electrical wire (C) Daniel Friedman

This illustration of frayed fabric-insulated electrical wire powering the ceiling light shown below were provided by and used with permission of Roger Hankey, a Minnesota home inspector.

1950's era fabric covered copper & tinned copper electrical wire being salvaged (C) InspectApedia.com D.D. Frayed electrical cord ceiling light fixture (C) InspectApedia Roger Hankey

Below: These photographs of a variety of fabric-covered rubber & plastic-insulated conductor electrical wire including copper and tinned copper from the 1950's were provided to us by a reader who planned to salvage this old copper wiring to sell for scrap. - D.D. 2016/09/12

1950's era fabric covered copper & tinned copper electrical wire being salvaged (C) InspectApedia.com D.D. 1950's era fabric covered copper & tinned copper electrical wire being salvaged (C) InspectApedia.com D.D. 1950's era fabric covered copper & tinned copper electrical wire being salvaged (C) InspectApedia.com D.D.

The conductors are themselves covered by a variety of materials: fabric over rubber, rubber, and plastic. We discussed the risk that some of these wires may have been insulated using asbestos.

OPINION: There was asbestos used in wiring as fabric sheathing and possible also mixed in with rubber insulation, as we have seen by researching some early wiring patents. In rubber you're not dealing with very friable material; if the wiring came from a movie theater or stage I'd be on higher alert. In any event taking some precautions not to make nor breathe a dusty mess would be smart, asbestos or no. If you were facing a big cost in any regard it'd be worth having a representative sample tested by a certified lab (see ASBESTOS TEST LABS at InspectApedia.com).

Also see ASBESTOS ELECTRICAL INSULATION.

Knob & Tube Electrical Wiring

The earliest form of electrical wiring system in buildings in the U.S. was knob and tube: separate hot and neutral wires were hung in air, spaced 2 1/2" or more apart, and insulated from contact with wood framing by ceramic knobs or where wire had to pass through a wood framing member, ceramic tubes. Both of these are shown in our photo below. Knob and tube wiring diminished in popularity in North America by 1940, but continued to be installed as new work in some locations (including New York) until about 1975. This wiring as pre-existing or "old-work" electrical wiring, is still described in the U.S. National Electrical Code (2005) in Article 394.

Knob and tube electrical wiring detailed photo (C) Daniel Friedman

The knob and tube wiring shown above is discussed in detail at KNOB & TUBE WIRING where we discuss assessing the condition of knob and tube wiring and issues concerning improper extensions of knob and tube circuits.

Plastic or Nonmetallic Cable (NMC) Insulated Electrical Wiring: Romex Cable Wiring

Dini (2006) notes that NMC or plastic-insulated wire or "Romex" has been in use in the U.S. since about 1926. Plastic NMC began replacing both rubber wire insulation and fabric-based wire insulation in the U.S. in the 1950's. PVC here refers to plastics based on polyvinyl chloride.

NMB_3-wire_with_Ground_Stripped (C) Daniel Friedman

Plastic or thermoplastic nonmetallic cable such asa that shown below, still referred to by many electricians as "Romex" cable, has been in use since the 1960's and in the U.S. became very widely used in new residential construction by 1970, completely replacing fabric-based wire insulation products. (FABRIC NMC WIRE INSULATION IDENTIFICATION). But in some jurisdictions including some large cities, local electrical codes require metallic armored cable (ARMORED CABLE or BX WIRE IDENTIFICATION) or electrical conduit rather than plastic NMC.

Also see ROMEX SPLICE CONNECTORS

Rubber-Insulated Electrical Wires

Thomas A Edison electrical wire patent No. US 470924, 1892 - U.S. Patent Office

It's fair to say that rubber in a somewhat different form was the first electrical wire insulating material, at least in the U.S., dating from Edison's 1892 patent from which we excerpt this part of Edison's wire insulation description:

The object of my invention is to effectively insulate wire, so that it will be waterproof and capable of being used in moist places and even under water without detriment to its insulating qualities, and also fire-proof, so that if by accident the wire becomes red-hot the insulating-covering will not be set on fire and burned, but only oxidation Will result, which will leave the wire pyro-insulated.

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.

But actually earlier electrical power cable and wiring insulation appeared as rope, tarred fabric, and even wood. However the rubber insulated wire illustrated by Edison's 1892 patent represented the first economical branch circuit conductor wire insulation approach that could be mechanically and economically produced in high volume.

More electrical generator equipment dating from Edison's day and still on display at the Pratt Institute can be seen at STEAM BOILERS GENERATORS CONTROLS, PRATT.

Mixed-Media wire: rubber-insulation over plastic-coated copper electrical wires

Rubber insulated extension cord wiring over plastic-insulated electrical wires (C) Daniel Friedman

Above: This wire was a short section of extension cord that had been used to connect a permanently-mounted fluorescent light fixture to power by plugging it into a wall-mounted electrical receptacle.

Below: this is a sample of plastic-insulated multi-strand electrical wire that was encased in the rubber jacket shown above. When the light failed to operate the author, on disassembly, found that the insulation on this wire was badly deteriorated, crumbling, and unsafe.

Deteriorated plastic-covered electrical wire from ca 1962 (C) Daniel Friedman

In our rubber and fabric wire insulation photo below you can see that inside the outer rubber wire jacket these conductors were insulated by fabric-covered rubber. The color codes (white = neutral, black = hot) can be faded and hard to recognize on these wires unless you strip back more of the insulating jacket. The wire shown below combines the hot and neutral wires in an external rubber jacket. But the earliest electrical wiring systems in the U.S. used the knob and tube system. See KNOB & TUBE WIRE IDENTIFICATION in this article or for details about knob and tube wiring see KNOB & TUBE WIRING

Rubber insulated conductors in an older fabric-jacketed electrical wire (C) Daniel Friedman

Sometimes you may find tinned-copper electrical wire in these older conductors. Don't mistake tinned-copper for aluminum electrical wiring.

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 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.

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".

Original DC electrical wires from beneath New York City Streets  (C) Daniel Friedman

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.

Original DC electrical wires from beneath New York City Streets  (C) Daniel Friedman

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)

Theater Electrical Wiring

In theaters where electrical wiring is often temporary, we often find surprising and possibly unsafe installations. The rubber-coated wires shown below were observed in a New York theatre and looked better than what my brother-in-law Matt, a theatre electrician, could produce.

Theater fires are particularly dangerous as there is likely to be a crowd stampede to exits, poor lighting, and lots of combustible materials. In my home town, Richmond VA, the Hippodrome theater, opened in 1914, caught fire in 1945 when I was just two (so I'm not responsible). The fire was thought to have been electrical in origin.

Theatre wiring (C) Daniel Friedman

The U.S. NEC addresses theater wiring in several articles such as Article 530 - buildings or portions thereof used as studios using motion picture film or electronic tape more than 7/8" in width, Article 540 - wiring for motion picture projector rooms, and others.

See ELECTRICAL SAFETY in the THEATRE [PDF]

Older homes often have electrical receptacles and fixtures that are ungrounded, and many local codes do not require that they be rewired so they're grounded. Still, grounding is worth adding to your system because it adds protection against electrical shock.

Tinned Copper Electrical Wire

Fabric & rubber insulated copper wire (C) Daniel Friedman Paul Galow

Above the same rubber-insulated electrical wire discussed earlier is also used to illustrate the dull silvery colored metal wire observed where tinned copper electrical wiring is installed.

Watch out: tin-plated copper wire is a completely different product that, because its conductors sport a thin plated silver colored surface, might be mistaken for unsafe aluminum wire. It is not aluminum and it is safe unless, as with any electrical wiring, it has been damaged in some manner.

Not all rubber insulated copper wire is plated, but if you suspect that the silvery-colored wire is plated copper, it's easy enough to determine: with the wire disconnected from any power source, scratch the silver colored surface of the rubber-insulated wire and you'll see its red copper interior.

In REDUCE THE AL WIRE RISK: DETAILS, as well as in Aronstein (2011). There Aronstein describes plated-copper wire as:

Plated copper wire [tinned copper wire] is relatively common in older homes, and it looks like aluminum wire. It was commonly used with rubber-based insulation. Identification can be made by careful inspection of a cut end of the wire. In general, plated copper wire would not be present in nonmetallic sheathed cable ("Romex"), it is most generally found in metallic sheathed cable ("BX"). Cable of the "BX" type is not likely to contain aluminum wire. - Aronstein (2011)

At TINNED COPPER ELECTRICAL WIRE we provide additional discussion of how to avoid confusing tinned copper wire or tin-plated wire with aluminum wire such as the tinned copper multi-stranded wire shown below.

Tinned copper multi-strand wire ca 1960 (C) Daniel Friedman

Wireduct or Wire Loom flexible conduit

Wireduct or wireloom for electrical restoration (C) InspectApedia

Above we see both older fabric-covered electrical conductors and newer plastic-insulated wires in an electrical panel. The bare copper wire that is nearly black was a clue in tracking down a neutral and ground wiring failure at this building

. The heavy fabric braid wires shown in the left of this photo may be examples of Wireduct, also referred to as All-Weather Loom. Wire-loom or all-weather loom was sold as a non-metallic flexible conduit for protection of electrical wiring in buildings.

Wireduct all-weather loom wire insulation was produced in sizes from 1/4" to 2 1/2" in diameter and was described as having a flame-retardant finish and low moisture absorption.

The asbestos "wireloom" shown earlier on this page may be an example of this product too, designed for improved flame resistance in theaters. You may find wireduct or wire-loom on knob and tube electrical wiring systems as well as other older building electrical wiring.

Wire loom & open splices in an attic (C) InspectApedia Laurie

In the unfortunate electrical wiring situation shown above, a reader mailed us this photo of wire loom-wrapped electrical wires and splices left exposed in the floor of her attic. We caution that with this sort of electrical work visible, one must worry about what other work was done on the building by the same installer.

Wire Loom is still sold as a cabling protection sleeve made in its current (2016) form as a colored nylon flexible slit corrugated tubing or as black polyethylene flexible tubing. As we illustrate above, asphalt-impregnated cloth wire loom is also available and is used in antique and original restoration work (photos adapted from EBay advertisements 2016/02/10). - Thanks to home inspectors Roger Hankey and Kevin O'Hornett for added details about wire-loom insulation, 2016/02/09

Below: a non-split wire loom: Whittaker Fabric Wire Loom, 3/8" diameter. This is an asphalt-impregnated cotton wire loom typically used in automotive applications. Some antique wire loom products or wiring sleeves are constructed with a combination of asphalt-impregnated cotton/poly paper blend coated with asphalt for moisture resistance.

Wire loom or wireduct asphalty impregnated flexible coth conduit (C) InspectApedia

 

Special thanks to Minnesota home inspector Roger Hankey for assistance with material for this article. Roger Hankey is principal of Hankey and Brown home inspectors, Eden Prairie, MN. Mr. Hankey is a past chairman of the ASHI Standards Committee. Mr. Hankey has served in other ASHI professional and leadership roles. Contact Roger Hankey at: 952 829-0044 - rhankey@hankeyandbrown.com. Mr. Hankey is a frequent contributor to InspectAPedia.com.

Safety Warning: Do not attempt to work on your electrical wiring, switches, or outlets unless you are properly trained and equipped to do so. Electrical components in a building can easily cause an electrical shock, burn, or even death. 

Even when a hot line switch is off, one terminal on the switch is still connected to the power source. Before doing any work on the switch, the power source must be turned off by set­ting a circuit breaker to OFF or removing a fuse.

See SAFETY for ELECTRICAL INSPECTORS and ELECTRICAL WIRING BOOKS & GUIDES

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Or see ASBESTOS ELECTRICAL INSULATION

Or see ELECTRICAL GROUNDING in OLDER HOMES

Or see ELECTRICAL INSPECTION, DIAGNOSIS, REPAIR - home

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Publisher's Google+ Page by Daniel Friedman