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#28
A great article on arc-faults.

Arc-Fault Circuit-Interrupter Protection – Advanced Technology to Reduce Electrical Fires

Bryan P. Holland, MCP.
NEMA Codes & Standards

Smoke alarms and fire extinguishers are examples of emergency equipment used in homes to take action when a fire occurs. However, an arc-fault circuit interrupter (AFCI) is a product that is designed to detect arcing faults in a circuit and turn off the electrical system before it becomes an ignition source. Conventional overcurrent protective devices cannot detect these hazardous arcing currents that have the potential to initiate fires. Electrical fires take many lives, damage or destroy significant amounts of property, and often occur in areas of the home that are hidden from view or early detection.

Electric arcing creates intense heating that can ignite surrounding material, such as wood framing or insulation. The temperature of these arcs can exceed 10,000 °F. An AFCI device uses advanced electronic technology to monitor the circuit for the presence of these “hazardous” arcing conditions. Some equipment in the home, such as a vacuum cleaner or refrigerator, naturally create electric arcs. This is considered to be a normal arcing condition. Another normal arcing condition that can sometimes be seen is when a light switch is turned off or when an electric cord is unplugged.

A hazardous arc occurs for many reasons including damage to conductor insulation from nails, screws, sharp points, or even furniture placed on top of an appliance or lamp cord. When arcing occurs, the AFCI analyzes the characteristics of the event and determines if it is a normal or hazardous arc. AFCI manufacturers test for the hundreds of possible operating conditions and then program their devices to respond only to the hazardous arcing conditions. AFCI technology can be incorporated into circuit breakers, receptacles, appliances and appliance cords.

Research in the arc fault area began in the early 1990s when the U.S. Consumer Product Safety Commission (CPSC) identified a concern with the residential fires of electrical origin. A large number of these fires were determined to be in the branch-circuit premise wiring. It was these early studies that led to the first proposals requiring AFCIs, which were made during the development of the 1999 NEC. NEC Code-Making Panel 2 (CMP2) reviewed many proposals and heard numerous presentations on the new technology. After much data analysis and discussion, CMP2 concluded that AFCI protection should initially be required for branch circuits that supply receptacle outlets in bedrooms.

Subsequent editions of the NEC further expanded the requirements to now include all 120-volt, singlephase, 15- and 20-ampere branch circuits supplying outlets or devices installed in dwelling unit kitchens, family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, laundry areas, and similar rooms or areas. The most current edition of the NEC (2017 edition) also requires AFCI protection in dormitory units, guest rooms, guest suites, where branch circuits are extended or modified, and for the replacement of certain receptacles in a dwelling or dormitory unit.

Reducing fires of electrical origin and saving lives is an important responsibility of the entire construction and regulatory community. Applying technology to improve the electrical safety of the home is a wise investment for both the homeowner and the community at large. Through extensive product testing and the proper application of the NEC requirements, AFCIs will provide superior protection against arcing faults and is the advanced technology to reduce electrical fires.

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