What is Arc Fault?

by Frank G. Ross

 The term “AFCI” stands for Arc Fault Circuit Interrupter. AFCIs are fairly new – developed within the last decade or so.  Their purpose is to protect against fires caused by unwanted arcing in the home electrical system. Arcing faults are one of the major causes of home fires.  According to the Consumer Product Safety Commission, over 40,000 fires annually are attributed to home electrical wiring. These fires result in over 350 deaths and over 1,400 injuries each year.

Arcing is the flow of electricity through the air from one conductor to another.  It can occur when a plug is pulled from a socket or when a switch is opened.  This is normal and generally not a problem.  The problem arises with arcing faults which 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. 

When arcing happens as a result of these less than desirable conditions, it generates elevated temperatures which can lead to ignition of nearby combustible materials such as wood, paper or carpet.

Unlike conventional circuit breakers which only respond to overloads and short circuits, AFCIs use unique current sensing circuitry to discriminate between normal and unwanted arcing conditions.  When erratic current flow is detected, the AFCI circuitry, which continuously monitors the flow of electrical current through the AFCI, trips the internal contacts.  The circuit is de-energized as a result and the potential for a fire to occur is consequently reduced.  It is important to note that although AFCIs have been found to be successful in preventing home fires from arcing faults, they cannot eliminate them completely. In some cases, it is possible for the arc to cause a fire before the AFCI detects the situation and interrupts the circuit.

Effective January 1, 2002, the National Electrical Code requires AFCIs for receptacle outlets in bedrooms.  Added protection will result if AFCIs are added for other circuits for new residential construction as well as in existing homes, especially older home where wiring may have deteriorated. AFCIs should also be considered wherever panel boxes are added or upgraded.

In addition to AFCI receptacle type, an AFCI/circuit breaker combination is available.   These units combine traditional overload and short-circuit protection with arc fault protection. AFCI circuit breakers should be installed by a qualified electrician.  The breaker can be installed in the panel box in place of the conventional circuit breaker and will protect one specific circuit. Unfortunately, homes with fuses instead of breakers are limited to the receptacle type AFCI. As an alternative, a separate AFCI panel box can be installed next to the fuse panel box.

AFCI circuit breakers (AFCIs) have a test button and look similar to ground fault circuit interrupter (GFCI) circuit breakers. AFCI receptacles also have a test button similar to a GFCI receptacle.  As with GFCIs, AFCIs should be tested monthly to ensure that they are working properly and providing the protection for which they were designed. 

Even though some receptacle designs combine GFCI and AFCI protection, the function of the AFCI should not be confused with the GFCI. The GFCI is designed to protect people from severe or fatal electric shocks while the AFCI protects against fires caused by arcing faults. The National Electrical Code requires GFCI protection for receptacles located in areas of the home that have a potential for the presence of water such as in bathrooms, garages, kitchens, near swimming pools and in crawl spaces and unfinished basements, as well as for all outdoor receptacles. A combination AFCI and GFCI can be used to satisfy the NEC requirement for GFCI protection only if specifically marked as a combination device.

Many homes I inspect do not have AFCIs, but I expect to seem them more often as homeowners discover their existence and choose to upgrade their receptacles.  As AFCIs become more common, the benefits seen should be significant, not only in terms of property losses and injuries caused by electrical fires each year, but also in the saving of many lives.

Frank Ross is a Certified Utah Home Inspector for Pillar to Post Professional Home Inspection and a full member of the National Association of Certified Home Inspectors and a member in good standing with the Utah Better Business Bureau.  Readers may contact Mr. Ross at (435) 867-6400 or frank.ross@pillartopost.com or www.pillarposthomeinspection.com