Electrical tape (or insulating tape) is a type of pressure-sensitive tape used to insulate electrical wires and other material that conduct electricity. It can be made of many plastics, but vinyl is most popular, as it stretches well and gives an effective and long lasting insulation. Electrical tape for class H insulation is made of fiberglass cloth.
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A wide variety of electrical tapes is available; some for highly specialized purposes. Electricians generally use only black tape for insulation purposes. The other colours are used to indicate the voltage level and phase of the wire. (In fact, the coloured tape is referred to as "phasing tape".) This is done on large wire which is available only in black insulation. When wires are phased, a ring of tape is placed on each end near the termination so that the purpose of the wire is obvious. The following table describes this usage.
| Tape colour | Usage (US) | Usage (UK – old) | Usage (International – new) |
|---|---|---|---|
| Black | Insulation Low voltage, phase A |
Insulation Low voltage, neutral |
Low voltage, phase B |
| Red | Low voltage, phase B | Low voltage, phase A | Sheath, 415 V 3 phase |
| Blue | Low voltage, phase C | Low voltage, phase C | Low voltage, neutral Sheath, 230 V |
| Brown | High voltage, phase A | Low voltage, phase A | |
| Orange | High voltage, phase B | Sheath, garden tools | |
| Yellow | High voltage, phase C | Low voltage, phase B | Sheath, 110 V site wiring |
| Green | Earth ground | Earth | |
| Green with yellow stripe | Isolated ground | Earth | |
| Grey | Low voltage, neutral High voltage, neutral |
Low voltage, phase C | |
| White | Low voltage, neutral High voltage, neutral |
Tape that is approved for electrical applications will carry an approval label from an agency such as Underwriters Laboratories.
As it is easily torn by hand, can be written on, and generally removes from smooth surfaces cleanly, it is useful for a number of other applications such as labelling (including colour coding) and temporarily attaching objects to one another. It can be torn by hand or cut with tools.
The original electrical insulating tape was made of cloth tape impregnated with Chatterton's compound, an adhesive material manufactured using Gutta-percha. This type of tape was often used to insulate soldered splices on knob and tube wiring.
In the early 1940s, vinyl plastic emerged as a versatile material for a wide range of applications, from shower curtains to cable insulation. A major ingredient in vinyl film was tricresyl phosphate (TCP), which was used as a plasticizer. Unfortunately, TCP tended to migrate, giving the surface of the vinyl film an oily quality and degrading every tape adhesive known. Research chemists and engineers at 3M set out to create a dependable, pressure-sensitive tape made of vinyl film that would have the required electrical, physical and chemical properties.
Experiments were conducted combining new plasticizers with the white, flour-like vinyl resin. Finally, in January 1946, inventors Snell, Oace, and Eastwold of 3M applied for a patent for a vinyl electrical tape with a plasticizer system and non-sulfur-based rubber adhesive that were compatible. The first commercially available version of the tape was sold for use as a wire-harness wrapping. Interestingly, this original black tape wasn't black at all. Tapes formulated for high-temperature were yellow, and later versions were white. White tape, because of its instability in ultraviolet light, was eventually replaced with black tape, although colored vinyl tapes are still used as identification and marking tapes. Black became the standard industry color for vinyl standard tape, primarily because of its ultraviolet resistance. Thicknesses originally were 4 mil (100 µm), 8 mil (200 µm) and 12 mil (300 µm). These were standardized to 7 mil (180 µm) and 10 mil (250 µm) in 1948.