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Asbestos electrical insulation:
History, manufacture, visual identification: how to recognize asbestos-based or asbestos containing electrical insulation materials in products & buildings - a visual guide to identifying asbestos in buildings.
Page top photograph: asbestos insulation on electrical wiring in a theater.
This articles series about the manufacture & use of asbestos-containing products includes detailed information on the production methods, asbestos content, and the identity and use of asbestos-containing materials. Page top photo shows asbestos used in an electrical motor.
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The following text is Adapted from Rosato (1959) p. 106-112  © 2013 InspectApedia.com
One of the major uses for asbestos paper as well as for such forms of asbestos as yarn, tape, lap, and loose fiber is in the field of electrical insulation. Asbestos was used in both higher voltage AC or DC electrical wiring as well as in low voltage wiring products such as telephone cabling.
[Click to enlarge any image]
The main reasons for the use of asbestos are its fire and heat resistance, electrical insulation properties, acid resistance, and durability. Electrical insulation is also used to protect the surfaces of conductors from such adverse conditions as moisture and chemicals, and to fill spaces where corona discharge is liable to occur.
In electrical applications, asbestos insulation is used with low iron content. All grades of crude and milled chrysotile fiber are predominately used.
The lowest iron content fibers
for use in the electrical field are available from ore deposits
in the North American Continent. ASTM specifications list
the total iron content for electrical grade products. Details are
at ASBESTOS IRON CONTENT.
Large quantities of asbestos are used to cover electrical wire in the traction type of electric motors and coils where there is a possibility of rising temperature damaging ordinary cotton coverings.
The general use of asbestos electrical insulation includes ordnance equipment (aircraft, missiles, etc.) oil burners, heating and cooking apparatus, lighting equipment, agricultural machinery, construction and mining machinery, hoists, oil field machinery, machine tools, portable tools, bakery machinery, food products 'machinery, textile machinery, paper industry equipment, pumps and 106 compressors, conveying equipment, blowers and fans, trucks and tractors, industrial ovens and furnaces, mechanical stokers, computers and cash registers, vending machines, laundry equipment, vacuum cleaners and units, refrigeration and air conditioning units, motors and generators, power transformers, switchgear controls, welding units, insulated wire and cable, lamps, radio, TV and radar units, x-ray units, railroad units, dental units, and signs and advertising displays.
Lightweight asbestos insulation is of primary importance on Naval and Maritime ships. Navy cable insulation is of particular importance; it is a combination of asbestos paper and textile products (lap, tape, etc.)
In the manufacture of multi-conductor cables, the single or paired conductors are cabled into required multiples, together with cushioning fillers in the valleys. These fillers are generally made with asbestos roving.
Specifications for Asbestos-Based Electrical Insulation Materials
Classes of Electrical Insulation Materials
|Organic, not impregnated||195|
|Inorganic, organic binder||265|
|Inorganic, silicone binder||355|
Watch out: This data is circa 1959 from AIEE and is not current; therefore the table is provided for historic reasons and not as a current standard for electrical insulation products.
Another classification which includes asbestos-electrical insulated products is given by the Underwriter's Laboratories, Inc. This laboratory classifies asbestos electrical insulating material as asbestos-insulated wire (460 12) and as asbestos-varnished cloth wire (460 13).
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?] -retardent cotton braid: an insulation consisting of varnished cloth and impregnated asbestos. The wire shown above is discussed at OLD ELECTRICAL WIRING TYPESData pertaining to electric shipboard cable which includes asbestos is given in the "Cable Comparison Guide," NAV- SHIPS 250-660-23 (1956) published by Bureau of Ships, Navy Department, Washington 25, D. C. and available through Government Printing Office.
The data pertains to Government procurement specifications MIL-C-915A (Ships), MIL-C-2194B (Navy), MIL-C-2681 (Ships), and MIL-W-16878B (Navy). All cables are identified by types.
The letters listed under types identify the first letters of the words used in describing the cable. Other letters identify construction of the cable. Some of these cables which incorporate asbestos are identified as follows:
Also see OLD ELECTRICAL WIRING TYPES where we illustrate non-asbestos varnished-cloth insulation on copper electrical wires.
Asbestos papers are very popular for use in the manufacture of miniature electrical component units. Miniature transformers can use asbestos papers. A 30 per cent reduction in weight has been obtained in Class-B transformers.
I [DF] have also found asbestos-paper insulated electrical wire inside of some older electrical appliances such as stove tops and toasters though more often we found braided asbestos cloth insulated wire in those locations.
World War II initiated many development projects specifically for developing inorganic paper products. Prior to 1940, no inorganic papers were commercially available. At present, there are four basically different types of inorganic papers commercially available; i.e., asbestos, mica, glass, and ceramic.
Asbestos papers are manufactured by Johns- Manville, Inc. under the trade name "Quinterra" or "Quinorgo"; by Raybestos-Manhattan, Inc. under the trade name "Novabestos"; and by General Electric Co. under the trade name "Terratex."
These basic paper products are available in many different forms which include combinations of asbestos-glass, asbestos-mica, papers backed with or sandwiched between other types of papers or fabrics and held together by an oleoresinous varnish, shellac, silicone, rubber, or other composite insulation structures. These combinations provide for increased tensile strength which is desirable in many of the cable or wire taping operations.
The chief function of asbestos [in electrical applications] is that of a separator or as a wrapping for wire insulation. Untreated paper is roughly equivalent to air as an insulator; when it is completely dry its resistivity is good.
Untreated paper can contain moisture since it has the characteristic of absorbing moisture from the air—a characteristic typical of other paper products. It is usually treated with a varnish or lacquer in order to eliminate the moisture problem. Where high temperature requirements are of prime interest, the paper is treated with silicone varnishes or fluorocarbons.
In the manufacture of asbestos paper, there is always continued interest and development in producing open asbestos fibers. Various methods of manufacture and various equipment are used in order to fiberize bundles of asbestos fiber. By opening the fibers, entrapped undesirable magnetite can be removed.
Manufacturing processes have also been developed which permit uniform blending of asbestos fiber with such synthetic fibers as glass. These types of products are used by electrical insulation manufactures and by the manufacturers of reinforced plastics and filters.
"Quinterra" is a pyrolysis-resistant electrical insulation made of highly purified asbestos. These electrical insulations greatly extend the life of electrical equipment. By permitting magnetic units to operate at higher temperatures, they promote savings in space, weight and materials.
The asbestos products enable electrical apparatus to withstand higher overloads; thus, they reduce the necessity for standby equipment. Their thin layers require less time and labor to apply and occupy less space than the extra thicknesses formerly employed to compensate for the loss of dielectric strength caused by heat. (Courtesy Johns-Manville Corp.)
Figure 6.1. Installation of Quinterra wrapped coils in electric motor armatur e[click to enlarge]
In transformers, their uses include barriers, core tubes, spacer sticks, end packings, interlaminates, interlayers, and wrappers. They have replaced metal cores in some resistors and conserve insulation in others.
In magnets, they insulate the ribbon coils, and form liners, spacers, and wrappers. Both wires and cables are wrapped with "Quinterra" and "Quinorgo" Typical motor wire insulation is shown in Figure 6.1.
Patent 2,626,213 describes a unique method of dispersing and forming asbestos papers. The Novabestos paper products produced are characterized by their ability to stretch and distort, both dry and wet, to a much greater extent than ordinary paper.
The smooth asbestos fibers in the paper allow more flow and better packing properties than the commercial organic paper products.
The Novabestos paper machine developed specifically for producing asbestos paper is similar in many respects to the conventional Fourdrinier machine. The asbestos pulp is picked up by a wire screen and carried over flat boxes operating under a vacuum of 2 to 8 in. mm.
The flat boxes remove 60 to 70 per cent of the water from the slurry. The next step in drying is a suction transfer roll operating under a vacuum of 12 to 15 in. mm. In this operation, another 5 to 10 per cent of water is removed.
From the suction transfer roll, the paper goes over a steam-jacketed drying roll and then over a windup drum.
The finished paper product has the appearance of snowy white paper.
I was curious if I could post [this photo of old house wiring at an electric light fixture] in order to ID potential asbestos insulation.
The pictures are of a closet light fixture I was uninstalling. - M.C. 6 Feb 2016
Most likely those are conventional fabric (non-asbestos) insulated wires. Fabric covered (non-asbestos) electrical wire that was black or silver was often comprised of asphalt-impregnated cloth on both the wire jacket and the wires themselves, with the wire insulation made of fabric-covered rubber. Do you also have photos of the markings on the wire's outer jacket?
The asbestos-based electrical wire insulation I've seen appeared as white or gray fabric (theater wiring such as is shown at the top of this page) or in a harder asbestos-impregnated plastic or rubber insulation on wires used in high temperature appliances such as toasters, range tops, ovens, clothes dryers.
Watch out: however as you'll read in the article above there was asbestos-cloth insulated wire of several types, and more-difficult to distinguish by eye alone is asbestos-impregnated cotton fiber wire insulation.
The amount of debris removed by trimming the wire is probably trivial in any event.
Also see OLD HOUSE ELECTRICAL WIRING for more examples of old wiring insulation types & photos.
I was wondering if house wiring ever contained asbestos. The wiring in my home appears to have an asphalt impregnated type covering almost looks like a snake skin. Could this contain asbestos? - D.T., Canada 10/4/2013
A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer about wiring (noting any markings, exact composition of its insulation, and perhaps data about its age) than we can give by email alone. You will find additional depth and detail in articles at our website.
That said I offer these comments:
Asbestos was indeed used in electrical wiring insulation, as discussed in the article above (ASBESTOS ELECTRICAL INSULATION)
and appears in our lists of asbestos-containing materials found at ASBESTOS LIST of PRODUCTS
Asbestos was in particular, more widely used in a more pure form in certain electrical wires exposed to high risk (inside of heaters, toasters, electric stoves, theatre wiring).
I would like to see sharp photos of your wiring, its external jacket, cross section of the insulation, and if occasion permits, an actual sample - those details would permit further comment or even testing of the material.
Depending on the age and appearance of the wiring about which you ask, it may be appropriate to treat it as PACM - presumed asbestos containing material. But don't panic. Usually asbestos hazards are minimized by leaving PACM alone unless it is friable, already damaged and / or subject to damage and is in an occupied space.
I suspect that unless there is a demolition project in progress, the asbestos exposure hazard from asbestos-containing residential electrical wiring is very low, perhaps below the limits of detection, both because of low friability of the typical (excluding my list above) application and insulation materials, and because wiring is normally enclosed in wall, floor, or ceiling cavities.
(May 2, 2014) Frank d said:
Does vacuum cleaner cord SVT have abestos? Or has it ever contained abestos?
Svt cord is a type of UL cord that they use in vacuums it's probably highly unlikely that they use asbestos in this type of application. Ami I right?
Asbestos was used in some electric wire insulation such as high temperature wiring in heating devices and stoves and in theater wiring.
Dillon (1942) and other of our citations given below describe widespread use of asbestos in electrical appliances, devices, and in their wiring and line cords.
So SVT electrical cords are basially a cord with a thinner insulating jacket, intended for use on vacuum cleaners - appliances that often want to use a spring-loaded spool to re-wind and store the cord when it's not in use. That thin-ness limits the use of the power cord to just certain applications.
Weber (1997) cites SVT components in older guitar amps that did contain asbestos but that asbestos use was in the amplifier's structure.
I don't know that that application speaks to being able to assert the use or non-use of asbestos whatsoever. My OPINION is that where heat is an extra concern (such as toasters) we might be more likely to find that asbestos was used in an appliance electrical cord. Heat may indeed be a concern, or rather heat tolerance, in a power cord that has also to use a thin insulating jacket for other reasons.
The specifications for electrical wire insulation have much to do with tolerating heat as well as other factors (flexing in power cords, moisture resistance, etc).
Asbestos was in fact mixed with rubber in some applications.
You might approach the question of whether a specific power cord contains asbestos more easily by stating the product's name, model, and date of manufacture, and if available the manufacturer could certainly answer the question. The alternative is to have a sample tested.
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. - reader anon by private email 2017/04/18
I was curious as to what it was, and it's 90% cellulose insulation as tested by Western Analytical Laboratories. The test for asbestos cost $30. U.S.D.
Now the $150 worth of scrap copper is safe to scrap. - Anonymous by private email 2017/04/25
2016/01/04 Mike said:
Would asbestos ever had been utilized in the telephone cable that has hundreds of copper conductors wrapped in paper and covered with a lead sheathing? Trying to know if this cable can be easily recycled.
I would not rule out asbestos on cable insulation, telephone or other wiring, depending on where it was intended to be used. Asbestos was used for fire protection in some telephone cabling as early as 1901 and continuing at least into the 1970's including as an alternative to the jute core wrap used on wiring that may have been then encased in lead or other metal piping.
I have found research describing asbestos exposure of telephone linemen, suggesting that asbestos was certainly used in some telephone cabling. And some patent disclosures concerning telephone cabling also included asbestos materials.
My house contains Black and Silver braided cloth wiring with the markings CRESFLEX 12 AWG printed on them. The actual conductors are coated in rubber or PVC and there is no ground. Does this wiring contain Asbestos? - posted at this web page 2017/12/23
It would be unusual to find asbestos insulation on or in Cres Flex residential electrical circuit wiring.
More likely you're seeing a fabric, perhaps with an asphalt impregnation and silver top coat. Naturally nobody can promise you a firm answer about asbestos content in an un-seen, un-tested material in an unknown building.
Still the risks are likely to be very low unless you're making a dusty mess.
Illustration above: Advertisement for Crescent Metallic-Sheathed Wire appearing in Salisbury, Frank. "The inhabitants of Mars." Engineering and science 18, no. 7 (1955): 23-32. This is NOT Cres Flex but was produced by the same company and without mention of use of asbestos in the wire insulation.
Cres Flex was produced by Crescent Insulated Wire & Cable who also produced a metallic sheathed wire depicted in an advertisement we show below.
Cres Flex, also written Cresflex in some literature, is a specific brand produced by the Crescent Insulated Wire & Caboe Company, a Trenton New Jersey company. Cres Flex was first trademarked in 1936.
A predecessor of later plastic-insluated electrical wire (NMC or “non-metallic cable”), Cres Flex is an older form of flexible-jacketed non-metallic electrial wire using a specially-treated fabric braid insulating jacket. Such wire has also been referred to more-generically as “Romex” and Loomwire.
Reader request for photos: photographs of Cres Flex electrical wire are needed for this article - please use the page top or bottom CONTACT link or post photos as a comment at the end of this page. - Editor
Nonmetallic Sheathed Cable: This material, known by such trade names as Romex, Cresflex, Loomwire, etc., is shown in Fig. 4-5, and consists of two or more Type R or Type T wires ; over each wire is a paper braid, and over all is a spiral wrapping of paper. The wires are then enclosed in an overall outer braid of cotton, which is treated with moisture-resistant and fire-retardant compounds.
The spaces that would otherwise be empty are filled with a jute or similar cord. - from Richter, H.P., “WIRING SIMPLIFIED”, [PDF] Park Publishing Co., original (C) 1954, re-issued in multiple editions, 25th Ed., based on the 1956 U.S. National Electrical Code.
By "Standard NMC" I mean to exclude high-temperature-resistant or heat-resistant or fire-resistant electrical wiring such as might be used in electric stove tops or heating appliances where asbestos might have been used.
This same text cites the use of asbestos in high temperature application such as the manufacture of Type SP wires:
Fig. 4-7. In Type SP, the wires are imbedded in rubber. The cord is durable, attractive.
A really tough and knock-about cord is Underwriters' Type S shown in Fig. 4-8. Each wire is rubber-insulated; the two wires are then bundled into a round assembly, the empty spaces being filled with jute or paper twine to make it round. Over all comes a layer of tough, high-grade rubber. Type SJ is similar except that the outer layer of rubber is thinner.
For flatirons and other devices delivering considerable heat, a special cord is required known as "heater cord." The most common type is Type HPD and Fig. 4-9 shows its construction. A layer of asbestos is applied over each wire before twisting. Over all comes a layer of rayon or cotton; the cotton is by far the more durable.
A patent search and literature search performed on 12/24/2017 did not find the word “asbestos” appearing in CresFlex patents.
We searched for use of the word Asbestos in Cres Flex wire product descriptions, searching for patents assigned to Crescent Insulated Wire & Cable CO., in Trenton NJ
The word “asbestos” was not found in the following
Other NMC patents without asbestos:
Note that other patents by other companies, Not CresFlex do include asbestos in wire product descriptions, typically for special applications. Examples are given below
On Monday, May 04, 1936, a U.S. federal trademark registration was filed for CRES FLEX by CRESCENT INSULATED WIRE & CABLE CO. INC., TRENTON. The USPTO has given the CRES FLEX trademark serial number of 71377968.
The current federal status of this trademark filing is EXPIRED. The correspondent listed for CRES FLEX is ? of *****, *****, ***** ***** . The CRES FLEX trademark is filed in the category of Houseware and Glass Products .
The description provided to the USPTO for CRES FLEX is NONMETALLIC SHEATHED CABLE FOR CARRYING ELECTRICAL CURRENTS. - Cres Flex Trademark Information, Trademarkia.com , Retrieved 2017/12/24, original source: https://www.trademarkia.com/cres-flex-71377968.html
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