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January 21, 2010

Electrical Definitions: AFCI’s – Arc Fault Circuit Interrupters

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-THE AFCI

 

An arc fault circuit breaker or interrupter (arc fault circuit breakers) is a circuit breaker designed to stop fires by sensing non-functional electrical arcs and disconnect power before the arc starts a fire. The arc fault circuit breakers should distinguish between a working arc that may occur in the brushes of a vacuum sweeper, light switch, or other household devices and a non-working arc that can occur, for instance, in a lamp cord that has a broken conductor in the cord from overuse. An arc fault in a home is one of the leading causes for household fires.Arc fault circuit breakers look like a GFCI/ circuit breaker (Ground-Fault Circuit Interrupter in that they both have a test button, although it is important to distinguish the difference between the two. GFCIs are designed to protect people against electrical shock, while arc fault circuit breakers are primarily designed to protect against fire.

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 year. 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 carpets. Arc faults may occur for many reasons such as worn electrical insulation or damaged wire, misapplied or damaged appliance cords and equipment, loose electrical connections, receptacle leakage, neutral leads pinched to grounded metal box, wet connections or conduit, shorted wires, wires or cords in contact with vibrating metal, overheated or stressed electrical cords and wires, or driving a nail into a wall and having it inadvertently hit a wire. 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. The possibility of arcing grows as a home ages since age and time will contribute to the possibility of these conditions occurring.

 

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 is intended to prevent fire from arcs. AFCI circuit breakers are designed to meet one of two standards as specified by UL 1699: “branch” type or “combination” type. A branch type AFCI trips on 75 amperes of arcing current from the line wire to either the neutral or ground wire. A combination type adds series arcing detection to branch type performance. Combination type AFCIs trip on 5 amperes of series arcing. Advanced electronics inside an AFCI breaker detect sudden bursts of electrical current in milliseconds, long before a standard circuit breaker or fuse would trip. A “combination AFCI breaker” will provide protection against1. Parallel arcing (line to neutral).
2. Series arcing (a loose, broken, or otherwise high resistance segment in a single line)
3. Ground arcing (from line, or neutral, to ground)
4. Overload protection (for resistance loads such as heaters. inductive loads such as motors may require additional overload protection)
5. Short circuit protection
 
-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 circuit conductors.

 

-INSTALLING AFCIs

 

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.

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