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.



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.



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.



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

circuit conductors.



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.



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.



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

combination device.