Arc Fault Circuit Interrupter
The “AFCI” is an arc fault circuit
interrupter. AFCIs are newly-developed
electrical devices designed to protect
against fires caused by arcing faults in the
home electrical wiring.
THE FIRE PROBLEM
Annually, over 40,000 fires are attributed
to home electrical wiring. These fires
result in over 350 deaths and over 1,400
injuries each year1. Arcing faults are one
of the major causes of these fires. When
unwanted arcing occurs, it generates high
temperatures that can ignite nearby
combustibles such as wood, paper, and
Arcing faults often occur in damaged or
deteriorated wires and cords. Some causes
of damaged and deteriorated wiring include
puncturing of wire insulation from picture
hanging or cable staples, poorly installed
outlets or switches, cords caught in doors
or under furniture, furniture pushed against
plugs in an outlet, natural aging, and cord
exposure to heat vents and sunlight.
HOW THE AFCI WORKS
Conventional circuit breakers only respond to overloads and short circuits; so they do not
protect against arcing conditions that produce erratic current flow. An AFCI is selective
so that normal arcs do not cause it to trip.
The AFCI circuitry continuously monitors current flow through the AFCI. AFCIs use
unique current sensing circuitry to discriminate between normal and unwanted arcing
conditions. Once an unwanted arcing condition is detected, the control circuitry in the
AFCI trips the internal contacts, thus de-energizing the circuit and reducing the potential
for a fire to occur. An AFCI should not trip during normal arcing conditions, which can
occur when a switch is opened or a plug is pulled from a receptacle.
Presently, AFCIs are designed into conventional circuit breakers combining traditional
overload and short-circuit protection with arc fault protection. AFCI circuit breakers
(AFCIs) have a test button and look similar to ground fault circuit interrupter (GFCI)
circuit breakers. Some designs combine GFCI and AFCI protection. Additional AFCI
design configurations are anticipated in the near future.
It is important to note that AFCIs are designed to mitigate the effects of arcing faults but
cannot eliminate them completely. In some cases, the initial arc may cause ignition prior
to detection and circuit interruption by the AFCI.
The AFCI circuit breaker serves a dual purpose – not only will it shut off electricity in the
event of an “arcing fault”, but it will also trip when a short circuit or an overload occurs.
The AFCI circuit breaker provides protection for the branch circuit wiring and limited
protection for power cords and extension cords. Single-pole, 15- and 20- ampere AFCI
circuit breakers are presently available.
WHERE AFCIs SHOULD BE USED
The 1999 edition of the National Electrical Code, the model code for electrical wiring
adopted by many local jurisdictions, requires AFCIs for receptacle outlets in bedrooms,
effective January 1, 2002. Although the requirement is limited to only certain circuits in
new residential construction, AFCIs should be considered for added protection in other
circuits and for existing homes as well. Older homes with aging and deteriorating wiring
systems can especially benefit from the added protection of AFCIs. AFCIs should also
be considered whenever adding or upgrading a panel box while using existing branch
AFCI circuit breakers should be installed by a qualified electrician. The installer should
follow the instructions accompanying the device and the panel box.
In homes equipped with conventional circuit breakers rather than fuses, an AFCI circuit
breaker may be installed in the panel box in place of the conventional circuit breaker to
add arc protection to a branch circuit. Homes with fuses are limited to receptacle or
portable-type AFCIs, which are expected to be available in the near future, or AFCI
circuit breakers can be added in separate panel boxes next to the fuse panel box.
TESTING AN AFCI
AFCIs should be tested after installation to make sure they are working properly and
protecting the circuit. Subsequently, AFCIs should be tested once a month to make sure
they are working properly and providing protection from fires initiated by arcing faults.
A test button is located on the front of the device. The user should follow the instructions
accompanying the device. If the device does not trip when tested, the AFCI is defective
and should be replaced.
AFCIs vs. GFCIs
The AFCI should not be confused with the GFCI or ground fault circuit interrupter. The
GFCI is designed to protect people from severe or fatal electric shocks while the AFCI
protects against fires caused by arcing faults. The GFCI also can protect against some
electrical fires by detecting arcing and other faults to ground but cannot detect hazardous
across-the-line arcing faults that can cause fires.
A ground fault is an unintentional electric path diverting current to ground. Ground
faults occur when current leaks from a circuit. How the current leaks is very important.
If a person’s body provides a path to ground for this leakage, the person could be injured,
burned, severely shocked, or electrocuted.
The National Electrical Code requires GFCI protection for receptacles located outdoors;
in bathrooms, garages, kitchens, crawl spaces and unfinished basements; and at certain
locations such as near swimming pools. A combination AFCI and GFCI can be used to
satisfy the NEC requirement for GFCI protection only if specifically marked as a