What is an AFCI?

An AFCI is a special type of circuit breaker that provides a higher level of fire protection than that provided by conventional circuit breakers,  AFCI stands for "Arc Fault Circuit Interrupter"

Why are they a good idea?

According to statistics quoted by the National Fire Protection Association, electrical problems account for approximately 70,000 fires annually.  A large number of these fires are caused by electrical arcing ("arc faults").  Conventional circuit breakers do not provide adequate fire protection due to arc faults. 

What is an arc fault?

An arc is the flash that occurs when the electricity "jumps" through an air gap.  The arc ionizes the air, creating intense heat.  The heat created by an arc can easily reach 10,000 degrees Fahrenheit.  At that temperature, the metal in the conductors is instantly vaporized.  The metallic vapor is conductive, which can then prolong the duration of the arc.

The intense heat of the arc can quickly ignite surrounding combustible materials, causing a house fire.

How do they work?

The AFCI breaker contains electronic circuitry which constantly analyses the wave form of the electricity passing through the breaker.  When a wave that corresponds to a hazardous arc occurs, the breaker trips, cutting off power to that circuit.

What causes arcs in the home?

Arcs occur when there are loose connections, when conductors get dusty or dirty, or when the insulation around the wires becomes degraded.  Arcs also occur when wiring is subjected to mechanical damage, such as a wire getting pinched in a doorway or scraped and abraded when underfoot or under a rug.

What should I do about nuisance tripping?

AFCI breakers are very sensitive, but they are designed to be able to differentiate between a hazardous arc and a non-hazardous arc.  Small, non-hazardous arcs can be produced by switches, vacuum cleaners, and other appliances.  

AFCI breakers have been rigorously tested under real-life conditions since 1999.  If you are experiencing nuisance tripping, there could be problems with your wiring.  Good wiring practices must be employed when installing AFCI breakers.  Shared neutrals can also lead to tripping.  If your AFCI breakers are tripping under normal use, have your system analyzed and corrected by a licensed electrician.

Do they need to be tested?

Yes.  Just like GFCIs, the AFCI should be tested monthly using the test button on the breaker.  Faulty equipment should be immediately replaced.