Twentieth Century Wire Insulation: History of Wire Harness Assemblies

Twentieth Century Wire Insulation

Wire Insulation drastically increased in popularity in the Twentieth Century.

Especially when advancing technology became more accessible.

The twentieth century saw the use of natural rubber compounds to insulate wires as the norm.

The development of PVC insulation came about in the 1930’s. PVC insulation was more common starting in the 1940’s.

PVC, Cresyl Phthalate, DEHP and other plastics were replacements for rubber as an insulator for wires and other parts starting in the 1950’s.

Different Types of Twentieth Century Wires

Plastic or Nonmetallic Cable Insulated Electrical Wiring: Romex Cable Wiring

NMC or plastic-insulated wire or “Romex” have 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 in polyvinyl chloride.

Plastic or thermoplastic nonmetallic cable still referred to by many electricians as “Romex” cable, has been in use since the 1960’s.

In the U.S., Romex cable became widely used in new residential construction by 1970. Therefore, completely replacing fabric-based wire insulation products.

However, there was preference for electrical conduit over plastic NMC.

Knob & Tube Electrical Wiring

The earliest form of the electrical wiring system in buildings in the U.S. was knob and tube.

Ceramic knobs support Knob-and-Tube wiring. It also, runs intermittently through ceramic tubes beneath framing and at locations where the wires intersect.

This type of insulation diminished in North America by 1940. However, instillation continued as new work in some locations until about 1975.

They became less common because of many problems.

These problems included the insulation being a fire hazard. It tends to stretch and sag over time. Also, they lack a grounding conductor.

Grounding conductors reduce the chance of electrical fire and damage to sensitive equipment.

Fabric Covered NMC Electrical Wire Insulation

The exterior insulation on fabric-insulated NMC electrical wires is often black, silver, or white.

The insulation of individual wires within the cable may be rubber or fabric-covered rubber.

The insulation may be plastic in later wiring products.

Coverage of the conductors is by a variety of materials. These materials include: fabric over rubber, rubber, and plastic.

Copper-Clad Aluminum Electrical Wiring

The photograph of copper-clad aluminum electrical wire shows the wiring sheathing markings.

Observation of this NMC or non-metallic-sheathed cable electrical wire was in a 1974 Edina MN townhouse.

Also, it had connection 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.

Furthermore, it is safe for use in homes. Providing of course, that the wiring has been correctly installed.

Aluminum Electrical Wiring Types

Typically, aluminum electrical branch circuit wiring was plastic-covered.

Aluminum wiring has been studied since about 1945.

It began appearing in homes in North American as early as 1965.

In that year, Kaiser Aluminum and Chemical Corporation began marketing KA-Flex solid-conductor aluminum wiring.

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


Wrapping It Up 

Thank you for taking the time to read our blog post on wire insulation.

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Finally, to learn about Wire Harness Assemblies, please click below:




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