Fire risks due to unintentionally energized metal structures

Improperly grounded electrical equipment can lead to a fire within a home. If electrical equipment in a home is not properly grounded, then an electric fault may cause metal structures (such as heating, ventilation, and air conditioning ducts, metal framing, or screws, nails, and bolts) to become energized without triggering an overcurrent protection device. Electrical connections between these energized materials and grounded objects create an unintended path to ground and can lead to prolonged self-heating that can cause ignition in combustible materials such as wood framing, cellulosic insulation, and other lightweight combustibles. Alternatively, molten metal that is capable of igniting lightweight combustibles can be ejected if the energized surface contacts a well-grounded objected. This article presents results from experiments performed to investigate conditions that cause fires as a result of stray energization of electrically conductive construction items. Resistances, types of nearby combustibles, and other factors were evaluated.