<Li> sacrificial ("arcing") contacts </Li> <Li> damping materials to absorb arc energy, either thermally or through chemical decomposition </Li> <P> Arcing can also occur when a low resistance channel (foreign object, conductive dust, moisture ...) forms between places with different voltage . The conductive channel then can facilitate formation of an electric arc . The ionized air has high electrical conductivity approaching that of metals, and it can conduct extremely high currents, causing a short circuit and tripping protective devices (fuses and circuit breakers). A similar situation may occur when a lightbulb burns out and the fragments of the filament pull an electric arc between the leads inside the bulb, leading to overcurrent that trips the breakers . </P> <P> An electric arc over the surface of plastics causes their degradation . A conductive carbon - rich track tends to form in the arc path, negatively influencing their insulation properties . The arc susceptibility is tested according to ASTM D495, by point electrodes and continuous and intermittent arcs; it is measured in seconds required to form a track that is conductive under high - voltage low - current conditions . Some materials are less susceptible to degradation than others . For example, polytetrafluoroethylene has arc resistance of about 200 seconds (3.3 minutes). From thermosetting plastics, alkyds and melamine resins are better than phenolic resins . Polyethylenes have arc resistance of about 150 seconds; polystyrenes and polyvinyl chlorides have relatively low resistance of about 70 seconds . Plastics can be formulated to emit gases with arc - extinguishing properties; these are known as arc - extinguishing plastics . </P>

A circuit has a continuous path through which charge can flow from a voltage source