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Whose Fault is it? Understanding Arc Faults

Most people realize that a building’s electrical system can cause a fire if misused or wired improperly. The Consumer Products Safety Commission (CPSC) has determined that annually more than 10% of all household fires are related to electrical systems. Nationwide, this is over 40,000 fires a year.

The CPSC estimates that of electrical system related fires, half are caused by “arcs” within a building’s wiring. As defined by General Electric, an arc is an unintentional electrical discharge, characterized by low and erratic current, that may ignite combustible materials. The heat and/or sparks that are associated with this discharge are often responsible for igniting building materials, furnishings, clothing, or other flammable materials nearby.

There are a number of items that can lead to an arc fault. Some of these are:

  • loose or improper electrical connections
  • failed or frayed appliance or extension cords
  • compromised plugs due to furniture placement
  • failed wiring insulation due to age
  • damaged wiring due to a nail, staple, rodent, etc.

The National Fire Protection Association (NFPA) is a non-profit group that advocates fire prevention and is responsible for publishing Codes and Standards that, among other things, affect how buildings are constructed. The NFPA has recognized the dangers associated with arc faults and the 2002 edition of their National Electrical Code (NEC) requires that arc-fault circuit interrupters (AFCI) be installed to protect all outlets in bedrooms. An AFCI device uses current sensing electronics to identify an unwanted arcing condition and de-energizes the circuit, thus eliminating the arc and reducing the potential for fire. Protective devices such as circuit breakers, fuses, and even ground-fault circuit interrupters (GFCI) are incapable of reacting to an electrical fault caused by low level arcing.

“The CPSC estimates that of electrical system related fires, half are caused by “arcs” within a building’s wiring.”

There are a few important things to consider when using AFCI devices. First, the NEC requires AFCI protection on the entire circuit. Although there are different types of arc fault interrupters recognized by Underwriter’s Laboratories, not all of them will protect the entire circuit and therefore, do not comply with the Code. The most effective way to meet the intent of the Code is to install integral AFCI circuit breakers within the panelboard or load center where the circuit originates. Second, the NEC requires AFCI protection on all 15 and 20 amp circuits that supply bedroom outlets. It is important to realize that the NEC considers receptacles and light fixtures to be “outlets”. Finally, while AFCI devices are currently required in bedrooms as a minimum, they are not prohibited from being used elsewhere.

Many experts strongly believe that the requirements for the use of AFCI devices should be expanded to include more locations in future Codes. The 2005 National Electrical Code is ready for release and will soon be adopted by cities and municipalities. Stay tuned to see how your home or facility may be impacted by new AFCI requirements.

– Mark D. Layfield, PE, LEED AP

Mark is a Principal, Licensed Electrical Engineer, Lighting Designer, and LEED Accredited Professional. Please feel free to contact Mark for further details regarding the above information.