Design Considerations

Section Contents:

Product Characteristics
Technical Data
Maintenance Requirements

Product characteristics. Vinyl's performance characteristics make it particularly well suited to demanding electrical applications. For example:

•Durability and mechanical strength. Cables and wires used in a building must often withstand a wide range of conditions, including dampness, exposure to chemicals and sunlight and wide temperature variations. Vinyl electrical components are formulated with customized ingredients that give the material the durability to perform under virtually any condition and in a multitude of applications. For example, the high abrasion resistance of vinyl wire insulation eliminates the need for a separate jacketing in many cases. Ultraviolet inhibitors give vinyl electrical products excellent weatherability. Vinyl can also be formulated to be resistant to oil, gasoline and most chemicals. Unlike many rubbers, it is inherently resistant to ozone. In rigid applications such as raceways and electrical switch boxes, it stands up to a wide range of conditions, protecting crucial wires from damage.

•Flexibility. Vinyl's ability to bend and twist without cracking makes it particularly suitable for electrical applications. Vinyl-jacketed wires and cables can be bent to allow for hooking fixtures and switches to the wire, or to be pulled through conduit. Even at low temperatures, vinyl remains flexible and easy to manipulate.

•Versatility. Not only can vinyl be formulated with a wide variety of performance characteristics, but it can also be made in virtually any color, allowing for easy identification. The surface can be matte or glossy, depending on a specifier's needs.

•Electrical properties. Vinyl has good dielectric strength, meaning that it can withstand relatively high voltages without breaking down, and high electrical resistivity, which makes it an excellent insulator. Vinyl-jacketed wires and cables are easy for an electrician to install and work with. Vinyl is lighter in weight than many alternative materials and can be stripped from the conductor with a minimum of effort.

•Fire performance. Because fires can begin in electrical systems, the fire safety of wire and cable jacketing materials must be carefully considered by the specifier and building owner. The fire behavior of vinyl electrical products depends in large part upon the exact combination of additives and modifiers used, and vinyl manufacturers make fire safety a top priority in formulating compounds for such products. In some cases, vinyl is the only material that can be used to meet the demanding fire safety requirements of the National Fire Protection Association (NFPA)'s National Electrical Code.

The high chlorine content of vinyl makes it inherently more flame resistant than most alternate materials used in electrical products. This property may be enhanced even further by adding flame retardants and smoke suppressants. Vinyl electrical products will burn when exposed to a significant flame source (typically above 600 F), but vinyl is slow to ignite and will typically self-extinguish when the flame source is removed. Other important factors to consider when evaluating fire performance of an electrical or building product include:

Heat release - Heat release is increasingly recognized as one of the most important factors in determining a material's flammability. When vinyl burns, it releases significantly less heat than many other insulation and jacketing materials. In fact, one European study found that the peak heat release rate for vinyl cables can be up to five times lower than that for fire-retardant non-halogenated cables. Vinyl's low heat release and tendency for char formation have been shown to slow flame spread.

Combustion toxicity - All fires are toxic, regardless of the building materials involved. Carbon dioxide (CO2) and carbon monoxide (CO) are produced in all fires, and CO, an odorless, colorless gas, is universally recognized to present the greatest toxic threat in any fire situation. The hazard of gases produced when vinyl burns is similar to the hazard produced by any other burning building material, including wood, metals or other plastics. Testing conducted by the National Electrical Manufacturers Association (NEMA) found no discernable differences in combustion toxicity between several materials used in wire and cable constructions, including vinyl, fluoropolymers and polyolefins. Repeated studies have demonstrated that typical fires involving vinyl produce HCl in quantities too small to pose any unusual hazard, and that fires involving vinyl are no more toxic than any other fire.

Corrosion - Gases produced during a typical fire are not only toxic, but are also sometimes corrosive to metal surfaces. But many experts agree that the area of greatest concern in a fire is not metal corrosion, but rather reliability of electronic equipment such as alarm systems, computers and other machinery. Evaluations of "current corrosivity" - the impact of smoke content on circuit boards - have shown vinyl cables to significantly outperform many non-halogenated cables. In general, studies suggest that materials with good fire properties - such as vinyl - have superior electronic reliability characteristics.
Technical data. The area of technical data which most significantly distinguishes vinyl electrical components from other materials is fire performance. There are four primary Underwriters Laboratories (UL) fire testing standards which illustrate vinyl's exceptional fire performance in enclosed areas, such as a shaft or plenum. They are:

•VW1 - A simple bunsen burner test. A small 500-watt flame source is applied to the wire or cable for 15 seconds and then removed for 15 seconds. These actions are repeated five times, the cable's behavior during the test is recorded. To pass the test, the wire or cable must not burn for longer than 60 seconds after flame application or ignite other materials placed below and above the sample.

•UL 1581 - Also referred to as a Vertical Tray Test.

•UL 1666 - Also referred to as a Riser Test. A flame source is applied to a vertically installed cable in a shaft for 30 minutes at the rate of 527,500 BTUs per hour. To pass the test, the cable cannot propagate flames higher than 12 feet, which in real fire conditions would prevent the spread of a fire from one floor to the next.

•UL 910 - Also referred to as a Steiner Tunnel Test, and the most stringent fire test a cable construction must pass to meet the National Electrical Code. A flame source is applied to a horizontally installed cable in a plenum environment for 20 minutes at a rate of 300,000 BTUs per hour. To pass the test, the flames must spread less than five feet and produce very little smoke.
It's important to note that this "hierarchy" of four fire tests, as they're known, are significantly more stringent than the only two tests required by the International Electrotechnical Commission (IEC), which regulates electrical products in Europe and other parts of the world. As a result, U.S. wire and cable products meet a higher standard of safety than anywhere else in the world. Vinyl electrical components can be formulated to meet all four of these stringent UL fire standards, and in some cases vinyl is the only jacketing material that can be used to meet these tests.

Installation. Vinyl can be formulated to meet the fire and physical requirements of every type of wire and cable used today, from building wire to fiber optic cabling. The presence of vinyl in a cable construction does not limit installation of the cable in any way, provided that the vinyl has been formulated to meet the applicable standards. For specific installation guidelines for wires and cables, refer to the National Electrical Code or the National Electrical Contractors Association.

Cost. Vinyl electrical components are reasonably priced, and are in most cases less expensive than other insulation materials, especially in the area of electrical power distribution. This helps to keep a building's construction costs under control, allowing an architect greater budget flexibility. Easy processability and ease of installation are two of the major factors contributing to vinyl's attractive cost. Likewise, rigid vinyl conduit and other cable management products are also generally less expensive that those made from alternative materials. For example, R.S. Means 1999 data indicates that installed costs for vinyl underground ducts for electrical and telephone wiring range from $4.41 to $22 per linear foot, depending on size and quantity. The same ducts made from galvanized steel range from $13.60 to $124 per linear foot. Similarly, R.S. Means estimates vinyl conduit installed in a concrete slab at $1.79 to $4.52 depending on size, while the same conduit made from galvanized steel ranges from $3.24 to $9.10.

Maintenance requirements. Vinyl electrical products are extremely durable and can withstand a range of tough conditions, including exposure to the elements, abrasion during installation and use and more. Otherwise, the presence of vinyl in a wire or cable construction has no impact on the maintenance requirements of the product.