Wiring Harness News WHN Sept-Oct 2020 WHN Sep-Oct 2020 - Page 34

34 SEPTEMBER/OCTOBER 2020 Wiring Harness News INDUSTRIAL INFO-TAINMENT In every issue of Wiring Harness News, Anixter will bring you informative articles about wire and cable technology. How Flame-Retardant Cable Insulations Work Choosing the correct flameretardant insulation for your application depends on the electrical and physical requirements of the application. It’s important to evaluate these requirements carefully since flame-retardant compounds can affect critical properties, such as flexibility, abrasion resistance, installation, temperature requirements, electrical properties, life expectancy, pulling lubes to be used and more. Components of Fire To better understand flame retardants, it helps to know what causes fire. There are three main elements necessary to create fire: oxygen, fuel and ignition. A fourth factor that can cause fire is heat, such as when overheated wires from a short circuit degrade insulation to the point that it creates combustible materials in both gas and liquid form. These materials combine with oxygen and provide ignition, which releases more heat and creates more combustible material to ignite. This cycle will continue until at least one of the three elements is eliminated. How Flame Retardants Work Flame retardants work by interfering with one or more of these three fire essentials by: 1. Eliminating the fuel 2. Cutting out the availability of oxygen by chemically reacting with the fuel 3. Reducing the amount of heat available to degrade the insulation Halogenated Flame Retardants Flame retardants used in wire and cable insulations are either halogenated or non-halogenated. Halogens are elements from group 17 of the periodic table and reduce flammability by free-radical reduction. A free radical is an atom or group of atoms with a single unpaired electron, usually produced by breaking a covalent bond. Halogenated compounds, especially bromine-based types, are the most commonly used flame retardants. They act to halt exothermic processes—how much heat is released by the cable—by trapping high-energy free radicals after they form. This cools the system by greatly reducing or limiting the supply of flammable gases. Brominated flame retardants