Identifying causes for certain types of electrically initiated fires in residential circuits

While there are many circumstances that can lead to residential electrical fires, it is useful and practical to identify and document potential hazardous conditions and provide physical explanations of electrically initiated fires. Failure modes for a variety of parallel and series arc faults are described along with circuit breaker response, electrical data, photos, and video frames to explain the conditions that led to a hazardous condition. This work identifies some of the various conditions that can create overheated hazardous conditions and shows how wire insulation is commonly the first to ignite. Conditions explored include bundled extension cords under rugs, abused NM-B at a load center entrance, broken wires and loose connections. Physical phenomena investigated include glowing connections, series and parallel arcing faults. Low and high current arc energies are discussed and compared to the combustible energy of volatile gases produced from wire insulation to illustrate the wide difference in the arc energy compared to chemical combustion energy from the decomposed PVC. Electrical wire insulation properties were also measured on various wire types to show the effects of thermal aging. Hardness of the wire insulation and cracking of the insulation was used as a measure of insulation lifetime at 140 degrees C. Copyright (C) 2010 John Wiley & Sons, Ltd.