While it’s usually hidden behind walls, in ceilings or in electrical fixtures, electrical tape performs crucial tasks. It can protect spliced wires, make quick repairs and properly label wiring, among other uses. But in terms of materials and specs, there is a world of difference between electrical tapes. Choosing the right solution could mean the difference between a durable, long-lasting tape application and a poor application that’s quick to fail.

Uses for Electrical Tape

Electrical tape is a common tape found in most contractors’ toolboxes. Its design and material composition make it superior for use on materials that easily conduct electricity.

The most common uses for electrical tape include splicing, phasing and generally providing mechanical or electrical protection.

Splicing

Electrical tape is typically used to protect wire splices. In the early days of electric wiring, connections were made by soldering wires together and insulating the connection with tape. While just twisting wires together and insulating with tape is still theoretically possible, it proves hazardous because tape can easily degrade and lose its insulating ability over time.

Modern electricians splice wires with wire nuts or other safe terminations. They often apply electrical tape at the point where the wire meets the nut or cap for extra insulation and security.

Phasing and Color-Coding

Electrical tape manufacturers usually produce tape in various colors for phasing and color-coding jobs. Phasing is an important practice that involves color-coding wires to indicate their voltage level and phase. This is especially crucial when a contractor wires a home or building and needs to pull wiring through openings in a wall. Phasing the wires prior to pulling them through eliminates any confusion over a wire’s phase or status as the ground wire.

The table below shows standardized electrical tape colors by geographical area.

Table 1. Common color-coded tape meanings, per location. Source: Engineering 360

Other Uses

• Electrical tapes can be used to make small repairs to damaged insulation, eliminating the need to replace the entire wire or jacket.
• It can also be used to wrap and protect wire harnesses and cables.

The Right Tape

Whether on the jobsite or maintaining machinery in a manufacturing facility, there are many uses for electrical tape. But, it’s important to note that not all tapes are created equal.

While some electrical tapes are designed for general purpose use, others are purpose-built to suit specific application. Contractors and engineers must consult the tape’s specs — including considering characteristics such as construction materials, weather resistance and dielectric strength — to determine if a tape is a good fit for the job.

Backing Construction

Electrical tapes are nearly always single-coated tapes. They consist of a 1-10 mil thick backing joined to a 2-5 mil thick adhesive. Vinyl backings, such as those comprised of polyvinyl chloride (PVC), are the preferred choice for electrical tape, and a major point of interest is whether the backings are monomeric or polymeric in construction.Figure 1: A cross-section of a generic, single-coated tape. Electric tapes typically have polymeric film backings and rubber adhesives. Source: Engineering360

Monomeric PVC films are made using short-chain plasticizers that do not bind into the film. The plasticizers may eventually migrate out of the film, causing brittleness, and the film itself has a tendency to shrink. Polymeric PVC films use long-chain plasticizers that bind well into the film, preventing migration and shrinkage.

From an application standpoint, this is not to say that polymeric backings should always be used over monomeric. Tapes with monomeric backings are suitable for simple splices and other general-purpose indoor or outdoor applications. Polymeric backings tend to be more expensive but impart better adhesion characteristics, especially in cold temperatures. Polymeric films also feature better elongation and holding characteristics in general, and are better suited to more extreme environments.

Related to backing construction, a tape’s thickness is also important to consider. Most standard monomeric and polymeric tapes for general applications are 7 mils thick, but applications calling for better tensile strength or high-voltage insulation may require greater thickness, often up to 30 mils or more.

Dielectric Strength and Breakdown

Dielectric strength is a key indicator of a tape’s electrical insulating properties. Expressed in volts per unit volume, it is the magnitude of voltage withstood without test piece destruction when a specific voltage is applied for a specified period of time. A higher dielectric strength indicates better electrical properties. PVC’s use as an electrical tape backing is largely due to its dielectric strength, which can reach nearly 60 kV/mm depending on material composition.

Dielectric breakdown is the voltage limit above which a short circuit may occur across the tape. The dielectric breakdown point occurs when an electric field causes a very high electron density, rapidly increasing conduction and causing material damage. It is important to consider the strength of the electric field in an application and ensure that this voltage is below a tape’s dielectric breakdown point.

UV and Weather Resistance

Most tapes can be use both indoors and outdoors, but some are better at handling environmental factors than others. Thicker polymeric PVC tapes typically retain adhesive qualities in extremely high or low temperatures. When selecting an electrical tape, it’s important to choose one with good resistance to chemicals, water and UV light, especially if it will be placed in an exposed, outdoor setting. Exposure to these elements can eventually cause the tape to crack, peel or wear out, leading to failure.

Know Your Tape Grade

Simply put, electrical tapes are available in several different grades with a wide range of specifications. Carefully matching a grade to an application results in improved safety and possible financial savings. For example, taping a difficult, high-voltage splice with a thin, low-grade monomeric tape could result in tape failure or even dielectric breakdown, causing rework at best and a dangerous situation at worst. Likewise, using a thick, polymeric tape on a simple low-voltage insulation jacket repair is safe and reliable, but wasteful due to the highly engineered tape’s cost, when a less expensive monomeric tape would do the job.

The Wrong Tape (or Application)

Figure 2: Home wiring causes nearly 50 percent of U.S. residential fires annually. Well-engineered, properly applied electrical tape that complies with published standards helps ensure a safe, hazard-free wiring system. Data source: 2010 USFA Fire Estimate Summary

Selecting the wrong tape for an application often leads to failure. Regardless of application or tape type, a tape constructed from inferior materials may unravel and fall off a wire or splice. At best, this results in rework if or when a contractor notices the tape has failed. In a phasing tape application, an older wire previously marked with a piece of colored tape that has failed and fallen off presents a mystery for anyone working on a future wiring project. In extreme cases, failed phasing tape could lead to confusing a high-voltage wire with a neutral or ground wire, a mistake no contractor wants to make.

Tape failure often occurs from using the wrong tape grade for an application’s environment. In freezing temperatures, inexpensive monomeric tape is likely to crack and become brittle, eventually failing. Cracked or peeling tape can allow water or other liquid to leak into the tape, causing electrical damage or total tape failure.

Tape application is just as important as type selection. Electrical tape is designed to be stretched during application to form a close seal with the substrate and tape backing itself. A tape closely fitted to the substrate results in superior adhesion and efficiency, as well as improved electrical insulation.

A stretchier tape is capable of more adhesion and staying power — the tape’s backing construction becomes crucial here. Monomeric backings are more likely to migrate, shrink and potentially fail, while a polymeric backing’s superior elongation, tension and adhesion results in a better seal. For this reason, tricky splices and high-voltage jacketing repairs should always involve higher-quality tapes with polymeric backings.

The Importance of Standards

Figure 3: A poor tape application. Electrical tape is designed to be applied close to the wire substrate. A tape with poor elongation and adhesion results in loose applications like most shown here. Source: Christopher Nunez / CC BY-SA 3.0

Because electrical tape failure can result in wire damage and fires, designing and using it according to published standards is crucial.

An Underwriters Laboratory (UL) listing is one of the gold standards for electrical tape. A UL Listed electrical tape complies with testing required by UL 510: Standard for Polyvinyl Chloride, Polyethylene and Rubber Insulating Tapes. UL 510 details testing for flame retardant qualities, sunlight resistance, physical properties, adhesive strength and moisture exposure, among others. This standard works in conjunction with the National Electrical Code (NFPA 70) to ensure safe wiring installations.

Canadian Standards Association (CSA) standard C22.2 is also an important benchmark for electrical tapes. The tape portion of C22.2 applies to PVC electrical tapes up to an operating temperature of 105 degrees Celsius, used on wires or cables up to 1,000 V.

ASTM D1000-17 also provides a host of test methods for electrical tapes. These include adhesion strength, break strength, dielectric breakdown, flammability, high-humidity environments, oil resistance and more.

There is more to a diminutive roll of electrical tape than meets the eye. Choosing the correct tape can be the difference between a safe, secure splice or insulation point and an unsafe, potentially hazardous situation. Even for non-insulating phasing and color-coding applications, contractors and electricians rely on electrical tape to stay in place where it is applied. A well-engineered electrical tape can be counted on to save time, money and more.