History of electrical wire & electrical wiring: how to recognize all types of old electrical wiring materials including knob and tube electrical wiring, cables, conductors including unsafe "extension cord" wiring.

We provide an index to photos of different types of electrical wire and also a table giving the timeline of years of use of different types of electrical wires or wire insulation and sheathing or jackets followed by a photo guide to all types of old building electrical wires.

These 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.

Page top photo: our home inspection client is pointing out a nice collection of antique knob-and-tube electrical wiring in an older New York home. Knob and tube wiring is still "legal" and can remain in use provided it is in good condition, has not been extended, damaged, or buried in insulation.

Photo Guide to Old Electrical Wire Types

"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."

- source: 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.

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.

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

• ELECTRICAL WIRE HISTORY TABLE / TIMELINE lists the types of old electrical wiring included in this article series.

For each entry in the "old wire history table" and also on this page at the electrical wire types listed alphabetically just below, we include links to example photos and to more detailed information.

• ALUMINUM ELECTRICAL WIRE - a fire hazard if not properly repaired
• ALUMINUM SHEATHED COPPER ELECTRICAL WIRE
• ARMORED CABLE BX FLEXIBLE METAL SHEATHED ELECTRICAL WIRE (Greenfield wire)
• ASBESTOS-INSULATED ELECTRICAL WIRE
• COPPER-CLAD ALUMINUM ELECTRICAL WIRE
• EXTENSION CORD WIRING - extension cord, lamp cord, zip cord run through walls & ceilings is unsafe
• FABRIC (CLOTH) INSULATED ELECTRICAL WIRE
• FABRIC INSULATED NMC WIRE - Black, Gray, Silver & White Colored Fabric Covered NMC Electrical Wire Insulation
• KNOB & TUBE ELECTRICAL WIRING - legal if ...
• METAL or PLASTIC CONDUIT ELECTRICAL WIRING
• METAL - ALUMINUM FLEXIBLE CONDUIT WIRING
• MIXED MEDIA ELECTRICAL WIRE - rubber-insulation over plastic-coated copper electrical wires
• PLASTIC INSULATED NMC Non-Metallic-Cable ELECTRICAL WIRING
• RUBBER INSULATED ELECTRICAL WIRE
• SOLID IRON PIPE ORIGINAL EDISON DC CABLE WIRING
• STAINLESS STEEL ELECTRICAL WIRING
• THEATER ELECTRICAL WIRING - may contain asbestos
• TINNED COPPER ELECTRICAL WIRING
• WIRE DUCT / WIRE LOOM FLEXIBLE ELECTRIAL CONDUIT WIRING

...

Electrical Wiring History Timeline

The table below gives approximate dates of origin and use of various types of electrical wire used in buildings. Also see the detailed article we provide for each electrical wire type, as more complete history will be provided in those articles.

Electrical Wire Types & First Use Dates
Wire Type	Dates	Comments & More Information
Telegraph Wires	1844	First commercial telegraph wires, Iron conductors, replaced by copper by 1913, low-voltage only.
Telephone Wires	1876	Early copper conductors, insulated, low-voltage only
Edison Solid Iron Tubing	1885 - 1910	Also: existing gas pipes converted to electrical use Details at SOLID PIPE EDISON DC CABLE HISTORY
Gutta Percha insulation	1885	Insulation on smaller conductors
Knob & Tube	1880 - present	KNOB & TUBE WIRE IDENTIFICATION Widespread use declined after 1940, still legal in some jurisdiction s Details at KNOB & TUBE WIRING
Paper wire insulation	1890 - 1910	Oil-impregnated paper Paper still used between PVC-insulated conductors & exterior PVC sheathing
Armored cable aka "BX" wire aka "Greenfield"	1898 - present	ARMORED CABLE or BX WIRE IDENTIFICATION BX WIRING GUIDE
Copper conductors	1913 - present	Possibly earlier.
Asbestos insulated wire	1920 - 1988	ASBESTOS WIRE INSULATION IDENTIFICATION Details at ASBESTOS ELECTRICAL WIRE INSULATION.
Rubber insulated wire	1922 - 1950	RUBBER WIRE INSULATION IDENTIFICATION Vulcanized rubber (VIR / VRI) insulation on copper conductors, covered with waxed braided cotton inside of an exterior sheath of fabric or in conduit from ca. 1922. Rubber exterior sheathing ca 1960, remains in current use in some applications
Tinned copper wire	ca 1925 -	TINNED COPPER WIRE IDENTIFICATION - sulfur in rubber attacked copper Details at TINNED COPPER ELECTRICAL WIRE
Lead wire sheathing	1930 - 1960	Flexible lead cable sheath covering rubber or pvc-insulated conductors
Cloth or fabric wire insulation ( NMC)	1933 - present	CLOTH WIRE INSULATION IDENTIFICATION Includes varnished & other fabric sheathed cables, rubber wire insulation, asphalt-impregnated & other fabrics, aka "Rag Wire" insulation Details at FABRIC NMC WIRE INSULATION IDENTIFICATION
Electrical conduit, metal	1940 - present	CONDUIT WIRE IDENTIFICATION Details at ELECTRICAL CONDUIT, METALLIC
XLPE	1950	Replaced paper insulation (medium voltage)
Copper electrical conductors with aluminum ground	1948-1960 (est)	UNIDENTIFIED Fabric Insulated Copper Conductors with Aluminum Ground
Aluminum electrical wire	1965 - 1973	ALUMINUM ELECTRICAL WIRE Details at ALUMINUM WIRING IDENTIFICATION
Aluminum-sheathed copper wire	1950 - 1976 (est)	See ALUMINUM SHEATHED COPPER ELECTRICAL WIRE
Copper-clad aluminum wire	1972 - 1975	COPPER CLAD ALUMINUM WIRE IDENTIFICATION Details at COPPER-CLAD ALUMINUM WIRE
Plastic insulated wire (NMC) aka "Romex"	1950 - present	PLASTIC NMC WIRE INSULATION IDENTIFICATION Earliest uses in Germany ca 1930 PVC sheath & wire insulation introduced 1952, i n wide use by 1965, various colors. Black from ca. 1960, white & other colors later. Includes Underground Feeder (UF) cables
Electrical conduit, plastic, flexible	1990 - present	Details at ELECTRICAL CONDUIT, NON-METALLIC
Lamp cord		EXTENSION, LAMP, ZIP CORD WIRE IDENTIFICATION
Stainless steel electrical wire	1960s - present	Special use where high mechanical strength is critical, e.g. in some space program applications. Discussed at STAINLESS STEEL + COPPER ELECTRICAL WIRE
Theater wire (asbestos?)		THEATER WIRE IDENTIFICATION
Wire loom conduit		WIRE LOOM or WIREDUCT WIRE CONDUIT
Wood wire moldings	1900 - 1928	Banned in North America in 1928

Notes to the table above

• Distinguish between insulation on the electrical conductors themselves, and the exterior sheath that covers two or more electrical conductors. Those are often different materials. For example a fabric exterior sheathing may cover rubber-insulated copper or tinned-copper conductors in older electrical wiring.
• Eland Cables, "What is the history of electrical cables?" - UK & Ireland, 020 7241 8787 sales@elandcables.com retrieved 2022/03/17 original source: https://www.elandcables.com/the-cable-lab/faqs/faq-what-is-the-history-of-electrical-cables
• Ferro, Maximilian L., and Melissa L. Cook. Electric Wiring and Lighting in Historic American Buildings. New Bedford, Massachusetts: AFC/A Nortek Company, 1984.
• See also ELECTRIC WIRE HISTORY RESEARCH & PATENTS below on this page

Aluminum Electrical Wiring Types

[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 America as early as 1965.

In that year Kaiser Aluminum and Chemical Corporation (KACC) began marketing KA-FLEX solid-conductor aluminum wiring (shown here).

Watch out: Unless it has been properly repaired or replaced, aluminum wiring in homes or other buildings is a serious fire hazard.

See complete details about aluminum electrical wiring

at ALUMINUM WIRING IDENTIFICATION

and at 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.

Copper Electrical Wire with Aluminum Sheathing under Plastic

Aluminum sheath under insulation on copper conductor wires

Pulled this stuff out of a house. Couldn't get over how difficult it must have been to install. Aluminum sheath, cloth covered copper., three wire has loom and filler. - On 2019-08-11 by Sean - -

Reply by (mod) - Aluminum sheath, cloth covered copper, three wire has loom and filler.

Thanks Sean we'll add that to the collection of wiring types - it'll help other readers - and I'll do some research to see what background I can find.

It would be helpful to know the country and city of the home where this was found as well as the age of the home and whether or not there are any special environmental concerns that might have led to the use of this wiring.

Also we need to see the stripped back wire ends to show other readers that this is copper wire in an aluminum sheath

I suspect this was a form of pre-wired "conduit" using semi-flexible aluminum tubing. I've included your photo and further comments and research in the article above on this page.

Solid but flexible metal conduit (with rules about just how it may be bent) is using solid aluminum and is one of several forms of pre-wired conduit that was probably intended for use in hazardous areas.

I've on occasion seen such industrial products used in the construction of private homes, perhaps because the owner or builder had a line on some "free" materials that fell off of the truck. So to speak.

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

The photo above illustrates two generations of metallic-sheathed armored cable or "BX" electrical wire. The vertical armored cable is an earlier generation of BX while the two flexible metal cables coming off the right side of the electrical box are its modern counterpart.

As the terms are generally used, synonyms for "BX" electrical wire include BX cable, armored cable, armor clad cable, and flexible metal conduit cable wire.

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

The flexible metal exterior of BX flexible armored cable provides considerable protection of the electrical conductors inside, guarding them from mechanical damage.

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.

BX wire appeared in the U.S. National Electrical Code in 1903, was popular and in wide use as early as the 1920s (earlier in some locations), very widely used in the 1950s, and remains in use today in new work where flexible armored cable is required, often by local codes.

Just above and also below: flexible aluminum BX or armored cable, stamped with AL, found in a 1955 Montreal home, courtesy of InspectApedia reader PE.

This aluminum sheathed BX cable contains a hot (black) and neutral (white) fabric and rubber insulated conductor, a paper wrapping, and a thin flat aluminum strip.

Modern BX or flexible metal conduit (FMC) electrical wire provides conductors that will be plastic-insulated rather than the older rubber.

[Click to enlarge any image]

Watch out: often we find that the rubber-insulated conductors in older electrical wire such as this BX, possibly a G.E. product, are so deteriorated that the insulation is crumbly and unreliable. If you can not strip back the wire to conductors whose insulation is intact then the wire should be replaced.

Grounding Conductor for BX Cable

Watch out: Notice that the wire in these the photo above does not include an approved grounding conductor. Some sources we reviewed claim, incorrectly, that the external flexible metal sheath on BX armored cable is allowed to serve as an electrical ground.

In our opinion that use is not reliable, and is unsafe. In a typical electrical circuit powering receptacles using BX there will be a connector or bushing at the cable's entry and exit to every electrical box.

The electrical connection between the cable exterior and the electrical box body is through the bushing set screw that is tightened against the BX cable exterior - an inconsistent and unreliable electrical connector whose credible function is to mechanically secure the cable to the box as a strain relief.

Here we show two of several types of connectors for use with armored cable/flexible metal conduit, using a set screw (above) and using a two-screw clamp connection (below).

Watch out: our now ex- brother-in-law Matt, a theater electrician, wired his NYC apartment using the NYC-required BX electrical cable. But being a strong fellow he over-tightened every single set screw connector at every electrical box.

When he turned on electrical power to the circuits none of the breakers would stay "on" because the over-tightened set screws plus the omission of the required plastic bushing insert in the open end of the BX caused the BX exterior edge to cut into either the hot or the neutral wire on every one of his connections.

The BX exterior became electrically live, shorted to the grounding conductor, and blew the breaker.

The flexible aluminum strip is also not usable by itself as a grounding conductor. (It would likely be under-sized.)

The flat aluminum tape that you see inside this 1950s BX and the thinner aluminum wire found wrapped around some newer BX cable is an internal "bonding strip" intended to improve the reliability of the external jacket of this cable should it become energized with electrical current.

When the cable is connected to an electrical box this tape or the smaller aluminum wire is bent back or wrapped around the outside of the cable before it inserted into the BX cable connector that secures the cable to the electrical box.

The electrical code does not explicitly address this question, as we excerpt from Texas' Electrical Code adoption of the NEC:

Article 320.108 Equipment Grounding Conductor

Type AC cable shall provide an adequate path for fault current as required by 250.4(A)(5) or (B)(4) to act as an equipment grounding conductor.

It is also important that you use the proper connectors to secure the metal BX exterior to a metal electrical box so that if the metal exterior does become energized it can also be connected through the circuit ground to earth, thus tripping a circuit breaker or blowing a fuse.

Watch out: When cutting BX the saw cut should be diagonally across one rib of the armor, and you need to take care to cut just the metal armor and not the wire insulation.

In the U.S., the National Electrical Code Article 320 Armored Cable: Type AC covers the installation and use of BX electrical wire.

See ELECTRICAL WIRE STRIPPING TIPS where we discuss proper wire stripping details and how to work with BX or armored cable.

Defects often found in the flexible conduit are discussed separately

at CONDUIT, ELECTRICAL.

Greenfield's original armored cable 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.

Greenfield Cable Patented Flexible Conduit

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

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 in this article:

CONDUIT WIRE IDENTIFICATION

1960 CIRCLE WIRE & CABLE Advertisement [PDF] in Electrical Engineering Magazine, Issue No. 9, Sept.-1960 p. 26A - excerpt shown just above, describes Circlesheath® Type RR armored cable for use underground (buried).

This advertisement describes the company's products as "Rubber covered wire & cable, varnished cambric cable, plastic insulated cable, neoprene sheathed cable, and cirtub EMT."

More Circle Wire & Cable products are described

at CIRCLE WIRE and CABLE Corporation

Below: an early advertisement for Cres-Flex armored cable or "flexible metallic-sheathed" wire:

Crescent Insulated Wire & Cable Co. also made fabric-insulated electrical wire described further

at FABRIC NMC WIRE INSULATION IDENTIFICATION.

Asbestos-Insulated Electrical Wiring

The asbestos-insulated electrical wiring wire loom or "flexible conduit" shown above is discussed in detail

at ASBESTOS ELECTRICAL WIRE INSULATION.

Asbestos electrical wire insulation is reported by some websites as "common" but I suspect its use was most common in applications where extra heat resistance and fire safety were a concern, such as theater wiring, electrical appliance wiring, aircraft wiring.

More examples of non-asbestos wire loom are given later in this article.

Cloth & Varnished-Cloth Insulated Electrical Wiring

Above: varnished-cloth electrical wire on the ballast used in a fluorescent light fixture in a 1960's home built in northern Minnesota.

See complete details about cloth or fabric-covered electrical cable or wire

at FABRIC NMC WIRE INSULATION IDENTIFICATION

Asbestos-impregnated type AVB cloth wiring insulation is discussed separately

at ASBESTOS ELECTRICAL WIRE INSULATION.

Metal or Plastic 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 unrestored 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 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.

To compare flexible conduit with armored cable, BX, or Greenfield wiring,

see ARMORED CABLE or BX WIRE IDENTIFICATION in this article.

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

For details about metal electrical conduit, please see our separate article

ELECTRICAL CONDUIT, METALLIC where we describe just about all of the types of modern electrical conduit materials including some not shown above.

Flexible Solid Aluminum Conduit Wiring

Above: metal clad cable using solid aluminum semi-flexible conduit pre-wired with fabric-insulated copper conductors, contributed by reader Sean 2019/08/11.

Sean wrote:

"Pulled this stuff out of a house. Couldn't get over how difficult it must have been to install. Aluminum sheath, cloth covered copper, three wire has loom and filler."

Excerpt from NFPA 70-2005

In Class I & II, Division 2 hazardous areas, the conduit itself cannot be used as the grounding means. A bonding jumper must be installed in accordance with NEC Section 250.102.

Flexible metal conduit is available with steel or aluminum armor in trade size 5 ⁄16" to 4".

With few exceptions where 5 ⁄16" and 3 ⁄8" trade sizes are used, Code prohibits use of conduit less than "d" trade size.

Bends in concealed work are restricted to 360 degrees total.

No angle connectors are permitted in concealed raceway installations.

Portions of this section reprinted by permission from NFPA 70-2005, National Electrical Code®, Copyright © 2004, National Fire Protection Association, Boston, MA. - retrieved 2019/08/11, original source:

METAL CLAD CABLE, ARMORED CABLE AND FLEXIBLE METAL CONDUIT [PDF] manufacturer's data sheet from Farnell Electric, http://www.farnell.com/datasheets/165782.pdf

Copper-Clad Aluminum Electrical Wiring

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

Extension Cord Electrical Wiring

Zip Cord or Extension Cord or surface-notched wires inside or behind plaster or drywall

Above we show an example of improper and unsafe electrical wiring: lamp cord or "zip cord" or "extension cord" has been routed through the building wall.

Our photo shows an electrical receptacle mounted just about 2" above the finished floor - which is ok except for the ADA requirements, but that zip cord

is not rated for use within building cavities. Not only is it unprotected, its insulation and wire gauge are not rated for use as a buried electrical circuit.

The 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.

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.

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.

Black, Gray, Silver & White Colored Fabric Covered NMC Electrical Wire Insulation

The exterior insulation on cloth or fabric-insulated NMC electrical wires are often black, silver, or white but may also be black or brown.

The individual conductors within the cable may be insulated in rubber or fabric-covered rubber or they may be insulated by plastic in later wiring products.

See details including the history of manufacturers of fabric-insulated wire along with dates, trademarks, and identifying photographs of a number of these cloth-insulated wire types.

at FABRIC NMC WIRE INSULATION IDENTIFICATION where we also discuss Paraflex & Paranite Insulated Electrical Wiring

Also see ASBESTOS ELECTRICAL WIRE INSULATION.

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.

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. 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 preexisting or "old-work" electrical wiring, is still described in the U.S. National Electrical Code (2005) in Article 394.

The knob and tube wiring shown above is discussed in detail

at KNOB & TUBE WIRING - topic home, 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.

Plastic or thermoplastic nonmetallic cable such as 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.

See 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

Also see PLASTIC ELECTRICAL BOXES

Rubber-Insulated Electrical Wires

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

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.

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

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

Power Cable for Electric Welder

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.

Solid Iron Tubing or Steel Pipe & Pitch Insulated Electrical Cables

Above: 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

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.

Details are

at SOLID PIPE EDISON DC CABLE HISTORY thanks to our friend Conrad Milster at the Pratt steam generator plant.

Stainless Steel Electrical Wiring

Here we illustrate and distinguish among aluminum, tinned copper, nickel, stainless steel, and other silver colored electrical wires.

Identify old electrical wire that contains one copper and one steel conductor

What does this old wire [photo above] have as conductors? One is copper but the other I'm told is nickel. How can I confirm it's nickel.?

I bought 2 wooden spools of this wire. A partial label says Philadelphia Insulated wire. I have scraped it down to the conductor and hope the attached picture shows it's solid through and not copper.

Both conductors are 1/16" thick. The silver wire is wrapped with red cloth while the copper wire has blue and then both are wrapped in the braided brown and silver cloth - On 2023-11-19 by Steve K -

Reply by InspectApedia Publisher - How to identify silver electrical wire conductor: may be aluminum, tinned copper, nickel, stainless steel, or an alloy

@Steve K,

Thanks for the interesting old electrical wire photo and question.

More likely there are two copper conductors, tinned or nickel plated. If the wire were actually nickel I'd be surprised to see 1 Cu and 1 Ni - you'd expect both to be the same.

TINNED COPPER ELECTRICAL WIRE explains how to distinguish tinned copper wire or tin-plated wire from aluminum wire.

There are a few special applications for steel or stainless steel wiring as we'll discuss further, below.

Nickel wire was quite hard, heat resistant, used more often in heating appliances and equipment than in building wiring where its cost for general electrical wiring of building circuits would have been prohibitive.

How old is your wire, where was it found: country, city, building type, building age, and any hints at its application?

Can you post a sharper view of the end view of the cut wire ends?

Have you tried scraping the conductor surface to see if it's tinned ? If so the tin coating will scrape off to reveal copper.

Are there markings on the wire insulating sheath?

What is the size of the conductors?

More by InspectApedia Publisher - Philadelphia Insulated Wire Company two colored wire - silver wire might be nickel or stainless steel or aluminum or an alloy

@Steve K,

Thank you for the wire photo; it's a bit blurry but yes, it looks as if that silver colored wire is solid through, not copper. It may be nickel or stainless steel, aluminum or another alloy. If it's quite hard it's probably not aluminum.

A magnet test might find that a steel wire with high iron content might stick to the magnet, though we've read that most stainless steel, with a high percentage of austenite is not magnetic.

I think your wire may be the product of the Philadelphia Insulated Wire Company, incorporated in Philadelphia PA in 1958. Some sources claim the company is still in operation while a foreign filing of the same corporate name as "inactive" was completed in California in 1980.

Some Philadelphia Insulated Wire Co. products were used in the aerospace industry. (See the example catalog page below).

[Click to enlage any image]

Additionally, some wiring products used copper-clad stainless steel to combine conductivity and strength.

It seems likely that your two-conductor (copper and steel) wire was a special-use product. Besides the fact that it does not include a grounding conductor, the fact that the two wires behave differently in conducting current lead to my OPINION that this special use product should not be used for building electrical wiring.

The use of steel in various forms, shapes, and applications in electrical wire and cable is detailed in this

• ENGINEERING DESIGN HANDBOOK: ELECTRICAL WIRE & CABLE [PDF] (1969) US Army Material Command Headquarters, original source: apps.dtic.mil/sti/tr/pdf/AD0865109.pdf

We've seen steel wires that reinforce copper conductors that are exposed to considerable strain such as overhead electrical wires or wires subject to a long pull.

1. If there is any text on the exterior jacket please photo that and post it here.

2. If we could obtain a sample of the wire (a few inches would be enough or more if there's text on the jacket) then our P.E. expert Dr. Jess Aronstein would be glad to examine it in more detail.

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.

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]

Tinned Copper Electrical Wire

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.

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), 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.

The heavy fabric braid wires shown in the left of this photo may be mistaken for Wireduct, also referred to as All-Weather Loom - shown below. It is not. This is a fabric- and rubber-insulated multi-strand electrical wire.

Wireduct or Wire Loom flexible conduit

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 two wire loom fabric conduit photos above were provided by InspectApedia.com reader Jared.

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.

In the unfortunate electrical wiring situation shown above, a reader mailed us this photo of white (probably-asbestos) 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 in Jared's photos, 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.

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: 952-217-1617 (MN) / 970-393-6604 (CO) - rhankey@hankeyandbrown.com. Mr. Hankey is a frequent contributor to InspectAPedia.com.

Old Electrical Wire History & Research

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Insurance company says cloth covered electrical wiring is not insurable

I live in Florida, which requires a four-point inspection for homeowners insurance. When we purchased our home, our inspector said some of our house was wired with cloth wiring.

At that time, it did not matter to us as we were still able to get home-owner insurance and he said we had the “good kind (safe) of cloth wiring”. Now we are trying to sell our home and we’ve been told that cloth wiring makes the home uninsurable.

I’ve been told this is not true cloth wiring, but plastic insulated wires with a cloth sheath. Does this constitute as cloth wiring? Is it formally defined somewhere in regards to the four-point inspection and insurance?

Picture is a wire clipping I found in the attic. On 2024-02-06 by Hunter -

Reply by InspectApedia Publisher - is cloth wrapped electrical wiring insurable

@Hunter,

Your electrical wiring uses plastic insulation on the conductors and an outer fabric or what you are calling cloth sheath. If the wiring is in good condition there's no rational reason to reject it based simply on its insulating material.

I don't know what document or authority or references being used for the complaint that you were told exists about cloth insulated wiring nor is there such a standard.

So if you can find a document or a citation I would be glad to research it and to respond further.

What are 3 sets of live wires in an electrical box?

How does 3 sets of wires in a box have power On 2023-12-29 by Anonymous -

Reply by InspectApedia Publisher - electrical box wires that enter and leave the box

@Anonymous,

Sorry because I really want to be helpful but I can't answer your question accurately with so little information.

I don't know what electrical box we are describing, a junction box for a receptacle or switch or a simple box or an electrical panel or at a piece of equipment.

I don't know what you mean by "set of wires" but might guess that if we're discussing a residential building, one "set" would include a hot (black), neutral (white), and ground (bare or green) wire.

But plowing ahead, here is a general description of electrical box wires that enter and leave the box:

It would be common for one set of live wires to enter a junction box (power-in on the black line) where in turn connections are made to feed power to one, two, or sometimes even more sub-circuits that are electrically "downstream" from that point.

Watch out: if you're doing electrical wiring and you're not trained in proper, safe procedures, you could be shocked or killed. So if you need help from an onsite electrician, don't be embarrassed to call one.

 

Why there is coax cable braid connection from capacitor plates to jumper ?

In the pic. attached; why there is coax cable braid connection from capacitor plates to jumper ?Is this for reducing the capacitance value? I saw this in some old circuits, is this necessary for today's applications?

On 2023-05-11 by SD -

On 2023-05-11 by InspectApedia Publisher - braided cable conductor from capacitor to jumper

@SD,

I think that the manufacturer chose a type of conductor that met the particular needs of the application. Braided wire is more resistant to breaking than solid conductor wire if ithe wire is repeatedly subject to movement or vibration.

I know that sounds a bit broad but what I mean to say is that where flexibility and/or movement are required a braided conductor can tolerate those where a solid conductor would not.

Examples of movement are not just moving a device physically around it would also include exposure to vibration and possibly even to temperature variation.

Flexible solid aluminum conduit wire

Found some of the flexible solid aluminum conduit wire in the crawl space of an old motel in northern BC, Canada. Until now, I hadn't ever heard of such a thing. I'll try to find a scrap peice to add pictures. On 2023-01-08 by Adam -

Reply by InspectApedia Publisher - flexible solid aluminum conduit wire in an old motel in northern BC, Canada

@Adam,

Thanks - it's especially helpful if you can photograph all of the imprinted text on the insulation and give the city in BC and the building's age.

Where to find wire used for electric radiant heat

I’m trying to find radiant heat wire that was used in ceilings I heard around the 1960’s. Single conductor with thick insulation.

Looks like a size 22awg wire from a home in California. Looking for a replacement wire that I could use to splice into. It is stapled onto drywall then gets mudded to hide in ceiling.

On 2023-04-17 by Alex -

Reply by InspectApedia Publisher

@Alex,

Please find your photo and our discussion now at

FYI see our articles on radiant heating starting at

RADIANT HEAT

I'll be grateful for further photos, comments, questions, suggestions.

I see lots of remodeling wire not routed correctly

@InspectApedia-911, I've noticed a lot of remodel wiring not properly ran through the studs and top or bottom plate using indoor wire laying next to and even attached to block to add a outlet or switch. The outer insulation (plastic) badly deteriorating after approximately 10-12 years laying on or next to damp concrete block below ground level.

Would using outdoor wireing and wire clips that keep it off the block wall and waterproofing the block with dry lock before insulation be as sufficient to using conduit? Yes it would be easier to just run pvc conduit or rubber conduit for sure and for safer as well and you wouldn't have to change to outdoor wireing tracing back to the junction point or adding another junction box you don't need.

But you never know what your going to find behind sheetrock or paneling. Hopefully they left the proper moisture distance away from the block and the stud wall and used a water barrier and ran the wiring only on using ,staples.

And through the 2×4s in the centers using metal plates on top an bottom plates to keep nails from coming in contact with the wire an use the wall boxes as junction boxes an not covering one up behind a wall without access to it.

Seen "Western Union" splices (not that good actually, most don't twist their wires together an use the push ins instead of the screws) (either like returning to fix it later or just don't care about causing a possibley deadly or costly fire) Use cover plates on everything. Junct. , plugs, switches, use wire nuts, don't over cram.

Wire locks boxsusing only electrical tape not stalpled on other side lying in the blown insulation and naked wires in walls cut off running off a 30-40 amp breaker hot asf*"k using "2" 3-12 wires b-110, b-110 2w- together 2grd together sometimes to the metal box. Which was a great idea.

Like running the entire shit shack off one 60 amp breaker, no grd. with metal boxes not even wrapping switches an plugs with elec. tape. Or not marking a white neutral turned hot in a box. Or my personal favorite. Homeowner doesn't yeild do not open or switch on breakers and isn't there to let you in the next morning.

Always put your black in the dirt or on a metal pipe ran under ground after you check it with your voltmeter b-2-blk, w-2-wht. first. On dirt use some plywood between you and the dirt floor as well as under your fiberglass ladder whether it's hot or not. Static elec. can build up in long runs especially in large jobs spaning long distances.

Discharge wire before handling. Buy some decent Kline stripers an pliers. At least 440vlt. rated. It's worth your life. On 2022-12-04 by Dave -

Reply by InspectApedia (Editor) - use wiring and electrical boxes that are designed and rated for use in damp or wet locations when needed

@Dave,

I certainly agree that if you were running wires in a damp or wet location it's absolutely essential to use wiring and also electrical boxes and devices that are designed and rated for use in damp or wet locations.

Otherwise the electrical system is quite likely to become unsafe.

What is the silver-colored strand behind all the wires at the top of this panel?

What is the silver-colored strand behind all the wires at the top of this panel? Is it aluminum wiring?

On 2022-10-27 by Bert -

Reply by InspectApedia (Editor) - aluminum wire (multi-strand) used for the two heavy black-insulated cables that bring power in to the panel

@Bert,

I'm not sure we're referring to the wire in your question, but certainly there is aluminum wire (multi-strand) used for the two heavy black-insulated cables that bring power in to the panel, at top left and right,

therefore

it'd be no surprise if along with those wires there were a multi-stranded aluminum grounding or neutral conductor connected to the panel neutral/ground bus at the top center of the box.

Need help identifying this wiring.

Looking for help identifying this wiring. House built early 1940s in the SF Bay Area. Seems to be copper wires with a rubber like coating wrapped in some kind of fabric.

On 2022-09-03 by John -

Reply by InspectApedia-911 (mod) - tinned copper wiring

@John,

It seem as if you have identified the wire except that I would add from the silvery surface coating that it looks like tinned copper.

Followup by John

@InspectApedia-911, Thanks. Based on this image is it possible to distinguish between knob and tube vs early Romex?

Reply by InspectApedia-911 (mod)

@John,

No, because many older electrical circuits omitted a grounding conductor - way past knob and tube - but an inspection of the building's electrical wiring wherever its visible can usually find some Knob and Tube if it's present.

Identify this wire in a receptacle or switch box?

Can someone help me identify this wire? I tried looking for any info printed on the side, I know it’s ungrounded, do I need to replace this to replace the switch to our ceiling fan and light?

On 2022-06-08 by Kinzie Oas -

Reply by InspectApedia-911 (mod)

@Kinzie Oas,

That's plastic insulated copper electrical wire, but old enough that there's no ground wire included in the wire jacket.

If the wire is in good condition and hasn't been damaged by overheating or some other event it's probably usable but you may need to run a ground for that circuit.

 

Wiring in old sewing machine connected to light fixture

Hello I have an old sewing machine, used once. Given to me by a friend. It is wired to fit into a light fitting. Is it possible to convert to a regular plug fitting.

The wires are one red, one yellow with green stripe. Thanks On 2022-04-17 by Christine Freer -

Reply by Inspectapedia Com Moderator - how do I change to a regular plug fitting?

@Christine Freer,

Sure. A "light fitting" - connected sewing machine is unfamiliar to me - please post a photo of the machine's power cord connecting-end and another (one photo per comment) of the whole sewing machine and a third of its data tag - that will help us research and answer more-fully.

But in general, if there are only two wires one will be hot (usually red or black) and the other should neutral (usually white but maybe that's your yellow-green).

A bit of following the wires into the machine to see which connects to the motor where will sort those out.

 

What is Rome-XLP underground cable from the 1960s?

A friend just replaced an old undergroung (urd) service that was 4/0 copper with a #2 open neutral direct buried. The cable says rome-xlp wire cable. The house was built in the 60's I would guess & they were upgrading the service.

He called me because he has never seen this type of cable as neither have I & I have been doing this kind of work for over 40 years. Just asking if anyone else has seen this before? On 2022-04-12 by Albert Schonauer -

Reply by Inspectapedia Com Moderator - Rome XLP electrical cable is rated for underground use

@Albert Schonauer ,

Rome XLP electrical cable is wire that is rated for underground use, that is, burial, using an XLP - cross-linked polyethylene insulation.

XLP wire is currently sold with stranded copper or aluminum conductors in larger sizes such as may be used for service entry wiring and in smaller sizes using a solid copper conductor for branch circuit wiring used where burial or resistance to moisture or to oil and gas is required.

XLP is popular for use as an alternative to EPR (Ethylene Propylene Rubber insulated wire) where a tougher insulation with more resistance to chemicals is needed.

Your 4/0 copper is sized for use as SEC or service entry wire just as you found. On the wire jacket you’ll see

ROME CABLE (UL) XLP XHHW-2 nnn AWG CU 600V E11486
where
nnn= the wire size such as 4/0

Rome Cable Corporation’s XLP wire was sold usually with a black or gray insulating jacket.

Keep in mind that XLP wire (rated for wet or burial) can also be used in dry locations and above-ground, as it’s also rated to perform against exposure to sunlight. It can also be run in conduit, raceways, and overhead. XLP USE wire is suitable where you might have run RHH and RHW-2 in either wet and dry residential or industrial applications.

In sum, XLP-use wire is similar to other XHHW building wire except for its additional rating for burial. In some references this same wire might be referred to as RHH/RHW wire meeting UL 854 for SEC applications.

Our Rome Cable Corp. XLP XHHW 12 electrical wire label shown here is for a smaller size, #12 AWG.

(Thanks to DWC Distributor Wire & Cable Co. distributorwire.dom for some of these details).

Identify and discontinue old doorbell wire

We purchased a home, and any wire we can see looks new. I went to pull off the nest doorbell to update it to use our account, and found the following wires. Notice the bare wire section. I wrapped it in electrical tape for now. What kind of wire is this, and should I be concerned? On 2022-04-06 by Jason

Reply by Inspectapedia Com Moderator - how can I fix old rubber and fabric wiring?

@Jason,

A doorbell wire or "bell wire" will normally be low-voltage, 24VAC, powered by a low voltage transformer somewhere in your home, often near the electrical panel.

You don't give the country, city, of location nor age of home, but I'm guess ing that that wire, as it looks like rubber and fabric, is pretty old.

If the damage is just at that connection and if you have enough spare length, cut back the damaged wire. Or if necessary, it's reasonable to wrap it in electrical tape.

If you can easily snake a replacement doorbell wire that'd be something to put onto your chore list.

If your worry is about asbestos, (not likely) see ASBESTOS ELECTRICAL WIRE INSULATION - live link in the Recommended Articles list.

 

Any value in scrapping old wiring?

Hows it going trying to see if anyone else has came across this very very old Lead/’possibly silver infused & or plated. Ive never in my life seen anything like it. And its thin stranded wire wirh just paper wrapped aroound each indiviual wire.

I have some stuff inch and a half and some stuff 2 inch just want to see if there’s any value in scrapping it distinctively On 2022-01-31 by Brad -

Reply by Inspectapedia Com Moderator

@Brad.,

Please try including a photo by clicking on the Add Image button and then Comment. That will help us answer your question.

If you are talking about 10 and copper wiring, I don't think there's a special scrap value Beyond its copper content.

 

What type of wiring is this in my fluorescent light and which is the ground wire?

What type of wiring is this where one white and one dark grey are coming from this one cord ? Which would be considered the ground wire?

On 2022-01-30 by Hello -

On 2022-02-02 by Inspectapedia Com Moderator - identifying fluorescent wiring

@Hello,

Without being on site with a voltmeter to test each wire to be absolutely certain that we know how they are used I'm afraid it's a bit dangerous for me to tell you what someone else connected.

However what you are looking at are high and low voltage wires in a fluorescent light fixture.

Take a closer look at the ballast, that's that big black rectangular object.

You should see a sticker right on the ballast that has the wiring diagram for that particular light.

You'll see that wires are sent from the incoming Supply voltage to the ballast and from the ballast to the terminals on the fluorescent light fixture and perhaps through a starter cartridge.

A Ground wire in your light fixture will normally be bare copper or possibly green.

If you use the on Page search box to search for the phrase

Fluorescent light wiring repair

You will find our articles that describe exactly how we have wired these fixtures in several configurations.

Post a photo of the drawing or schematic on your fluorescent fixture and I may be able to come in further.

 

Wring in mid 1950s Strawberry Box home

We live in a mid-50s strawberry box home and redoing the electrical.

There's an old disconnected 8 gauge fabric wire that travels from the basement (where the panel is) to the 2nd floor (and possibly to the attic. Does know anyone know what it could have been used for? On 2022-01-20 by Kim -

Reply by Inspectapedia Com Moderator - check old wiring's use and routing with DMM or VOM tool

@Kim,

Sorry but no,with no information at all about your home and not even a photo of the wiring and its markings, any guess is such wild speculation as to almost certainly be wrong.

When I find old wires in an old home and their use and routing is unknown,

I use a DMM or VOM or similar test tool to check for live voltage and even if the wire is "dead" I cap off the exposed wire ends for safety.

 

Safety of cloth and rubber insulated electrical wiring from the 1950s

I bought a house built in 1936, and the previous owner claimed the knob and tube wiring was replaced. Sadly, about 50% of the wiring is as pictured below.

Ungrounded and with cloth fiber insulation. It has a black cloth jacket, with two cloth insulated wires inside and a fragile rubber-like insulation against the copper. It's everywhere in the house

I'm concerned about the safety of this wiring and I would like to know if this is likely from 1936. I can't see any knob and tube wiring in the basement or the attic.

These wires are simply put through holes in the joists or stapled to the sides of them.

I see some more modern wire with a cloth outer jacket and modern plastic insulation, which I guess was from the 1950's or so, but the majority is as pictured. On 2021-12-12 by Nick -

I believe it to be tinned copper wire.

How much of a risk is the cloth jacket with the degraded rubber insulation inside? Do you believe this type of wire to be as much of a risk as knob and tube wiring?

Reply by Inspectapedia Com Moderator (mod) - Comparative safety of knob and tube electrical wiring and old fabric-insulated 2-wire circuits both without ground wire

@Nick,

I see copper wire - check that it's all copper - no aluminum

No-ground: not as safe as modern - you can add grounding

Condition: fabric itself isn't innately a defect, it's the condition of the wire that matters: cracked, damaged, missing, burned, overheated, rat-chewed insulation - needs new wiring in those cases

Watch out: Old electrical wires using rubber insulation are often sporting cracked fragile rubber that may crumble when the wire is handled. Poor-condition rubber wire insulation may reach that state from age alone or from having been exposed to harsh conditions or to overheating.

Continuing:

Apologies that I wasn't clear enough in my first try at answering.

The electrical safety with respect to the absence of a grounding conductor (ground wire) in knob and tube wiring and in an insulated wire that pairs the hot and neutral wires together but still with no ground, is identical.

The electrical safety of both electrical systems' wires in other regards turns on

- the condition of the wire and its insulation: if the insulation is damaged then it is less safe than when new and in some positions and conditions - such as where someone could touch it and be shocked or where there could be a fire risk - would be unsafe.

- my OPINION and that of some others in the field is that knob and tube wiring, because the hot and neutral wires were run separately and separated by several inches, was inherently safer than wires run together in the same jacket, should both wire sets suffer equal extent of damage to their insulation.

That's because the K&T wires are not only so far apart at most locations as to significantly reduce the risk of a hot-to-neutral short, but also because even where they are supported on or pass through wood framing, the wires are carried on porcelain insulators.

Arguing with myself by adding a dose of real-world conditions: knob and tube, generally never declared as "illegal", may in many buildings be at greater risk of overheating and thus risking a fire because over the ensuing life of a building from its original installation - run in open air - the K&T wires may now be completely covered by added-on building insulation.

That addition violates the original design that depended on being suspended in air to handle the heat generated by use of the circuit. The result exposes the wires to overheating and damaged insulation and thus increased hazard.

More is at KNOB & TUBE WIRING https://inspectapedia.com/electric/Knob_and_Tube_Wiring.php

Thank you for a helpful question.

Watch out: for an inch or so (at least) back from its connection to the device the insulation is damaged and partly-lost on at least the neutral wire. I can't see the rest of the wire's insulating jacket - check outside the electrical box and along the wiring passage.

Watch out: we see a bare copper ground but no proper ground wire connections.

 

When did manufacturers start using black-and-white as a color code for a 120 V electrical wiring?

When did manufacturers start using black-and-white as a color code for a 120 V electrical wiring On 2021-12-09 by Tim -

Reply by Inspectapedia Com Moderator (mod) - first standardized electrical wire color coding conventions found in the U.S. National Electrical Code in 1928.

@Tim,

From our research we found that standardized electrical wire color coding conventions entered the U.S. National Electrical Code in 1928.

Before that there were some standards such as requirements for wire insulation and wire sizes versus current or amps the wires could safely carry (without overheating to cause a fire) earlier, at least in New York by the NY Board of Fire Underwriters in 1881, and more national wiring standards were in place by 1893.

(The very first national electrical code in the United States, produced by the National Board of Fire Underwriters, was completed by 1897 but without wire color codes).

Currently the U.S. National Electrical Code is sponsored by the NFPA National Fire Protection Association - https://www.nfpa.org/

Is his is knob and tube or Romex ?

Trying to figure out if this is knob and tube or Romex On 2021-10-26 by Drew

[Photo above]

On 2021-10-26 by inspectapedia.com.moderator (mod) - is t

@Drew,

That looks like quite-old two-conductor electrical wiring, with no ground visible, just hot and neutral; its jacket or insulation looks as if it may be bitumen-coated fabric;

Where two wires are run in a common external insulating jacket, that's not knob and tube wiring.

But that does NOT mean that there are no knob and tube circuits nearby in the building. And I don't see a ground wire.

So we have 2-wire (with no ground) NMC (Non-Metallic-Cable or what you meant by "Romex") entering the electrical box.

Such wire might be connected to a knob-and-tube system, or not.

It would be useful to know the location of the building, country, city, and the building age.

Watch out: I see that the outer insulating jacket on this wire is cracked - it may be damaged and unsafe.

 

If receptacles have no ground hole what do I do?

if receptacles have no ground hole, does this mean I can't use a 3 hole receptacle On 2021-10-20 by Wayne Riley -

Reply by inspectapedia.com.moderator (mod) - Do not install a grounded "3-hole receptacle" on an un-grounded electrical circuit - or Label the receptacle "ungrounded"

@Wayne Riley,

On an ungrounded electrical circuit you physically can but legally and safety-wise should not install an electrical receptacle that has a ground hole or opening because you are fooling users into thinking that the receptacle is grounded and safe for equipment that requires a ground for safe operation when in fact that's not the case.

However before deciding that you have to buy a two prong un-Grounded receptacle to install in that location have your electrician open the electrical box and see if a ground is present.

Often there is a ground present and in that case you can install a grounded electrical receptacle or 3-hole receptacle.

If not it's best to install an un-grounded two-slot receptacle. In a pinch your local electrical inspector may allow installation of a grounded receptacle if it's clearly and permanently labeled as "NOT GROUNDED" or "NO GROUND"

...

Continue reading  at OLD HOUSE ELECTRICAL SYSTEMS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see OLD ELECTRICAL WIRING FAQs - questions and answers posted originally on this page

Or see these

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• AGE of a BUILDING, HOW to DETERMINE
• ALUMINUM WIRING IDENTIFICATION
• ANTIQUE & OLD ELECTRICAL RECEPTACLES
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• ASBESTOS ELECTRICAL WIRE INSULATION
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• ELECTRICAL GROUNDING in OLDER HOMES
• ELECTRICAL PANEL AGE
• ELECTRICAL RECEPTACLE TYPES
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• FABRIC NMC WIRE INSULATION IDENTIFICATION
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• OLD HOUSE ELECTRICAL SYSTEMS - home
• SOLID PIPE EDISON DC CABLE HISTORY

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OLD ELECTRICAL WIRING TYPES at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to ELECTRICAL INSPECTION & TESTING

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