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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.
Green links show where you are. © Copyright 2015 InspectApedia.com, All Rights Reserved.
The following text is Adapted from Rosato (1959) p. 106-112  © 2013 InspectApedia.com
[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
List of products using asbestos electrical insulation
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
Classification of electrical insulation by the American Institute of Electrical Engineers (AIEE) follows:
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).
Asbestos-Insulated Wire (460 12) Labels & Classifications
Asbestos-Varnished Cloth Wire (460 13)
Data 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:
Asbestos Paper Products as Electrical Insulation
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.
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.
Reader Question: did house wiring ever contain asbestos?
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 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.
Reader Question: asbestos used in vacuum cord SVT electrical cords?
(May 2, 2014) Frank d said:
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.
Research Citations Indicating Use of Asbestos in Electrical Wiring & Components
Asbestos, Its Industrial Applications - Rosato: Text & Chapter Index 
Continue reading at ASBESTOS FRICTION MATERIALS or select a topic from the More Reading links shown below.
Suggested citation for this web page
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
Question: asbestos hazards in arc welders?
(July 22, 2014) Mark Hunter said:
(July 22, 2014) Mark Hunter said:
Here is some research on asbestos used in arc welders as well as exposure of individuals using arc welders to asbestos
Question: Anaconda Dutrax C or G , type NM with 600v rating containing asbestos?
(Jan 5, 2015) Chuck said:
I'm sorry Chuck but just from your e-note I don't know the answer. If you face large possible costs you could have a sample of the wiring insulation tested by a certified asbestos lab (don't send it to me).
If the material is not damaged and is not in an area to be disturbed it might be left alone - lowest risk. Treat it as presumed to contain asbestos.
I would like to see some sharp photos of the wire and its insulation and markings - that may permit us to do some further research.
Question: asbestos used in PCB's (printed circuit boards)?
(Jan 13, 2015) Anonymous said:
I'm concerned my sega genesis and its game cartridges might contain in. The sega genesis came out in 1988 in Japan and 1989 here in the usa.
By 1988 it's unlikely you'd find asbestos in printed circuit boards. In older electronic equipment where asbestos may have been used in non-friable components most likely any asbestos release from those undisturbed components would be below the limits of detection.
Keep in mind that many electronic circuit boards include other highly toxic components that may be released, particularly during burning and possibly during demolition, as is the case as well with plastics in general.
PCBs are of course a separate hazard.
Thank you for the quick reply, i feel better about using my sega genesis now, thank you.
Question: asbestos report cites incandescent light bulb heat shields
29 January 2015 Renée said:
Renee I can't of course see your report (you can send it to me by email found at our CONTACT US link at page top or bottom) but an incandescent light bulb is an older technology or "conventional" light bulb that uses a heated filament - unlike newer LED or florescent bulbs. A heat shield fixture could be hidden away in any of many sorts of older light fixtures such as recessed ceiling lights or even a lamp socket. I'd be interested to know if your inspector actually saw such a fixture or if rather you are seeing a generic "CYA" remark in a boilerplate section of a report. In any event only if asbestos material is soft, friable, damaged, or easily damaged and tracked into a living area is an individual light fixture asbestos material likely to be a measurable risk.
Question: asbestos in 1970's table lamps?
29 January 2015 Mary said
We took an old table lamp apart from the mid 1970's. Would there be the possibility of any asbestos in the wiring or the felt glued to the bottom. There were some fibers in the lamp on the felt bottom when we tore it off.
Mary asbestos was used in some (not all) electric lighting lamps in lamp cords, sockets, insulators from at least as early as 1903 (See Sylvania (1903) below. Its use in felt used to avoid scratching a table surface seems unlikely. However asbestos was used in a paper form in some lamp bases - See Vaughn (1950) in my citations and See Lewis (1935) in the citations below for an example.
I'll add that if the lamp bottom looks like white or white-gray paper that might be asbestos paper. If it looks like green felt, it probably is green felt.
If it was gray white paper it may have been just cardboard or it *might* have been an asbestos paper.
Some examples of asbestos paper are at ASBESTOS PAPER DUCT INSULATION
Unless you really shredded the paper, I would guess that the amount of airborne asbestos from pulling off and throwing away a say 6-inch diameter piece of paper on a lamp bottom would be beneath the limits of detection. I would not be inclined to spend much on this but if you are very anxious it might help to collect a settled dust sample from the bedroom (using clear adhesive tape) and have that examined by a test lab. That cost is about $50. U.S.D.
At ASBESTOS TESTING LAB LIST you can find certified asbestos testing labs
At DUST SAMPLING PROCEDURE you can see how to collect dust samples to send to a lab.
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Web search 01/20/2011, original source: http://epa.gov/asbestos/pubs/verm_questions.html
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