Arc fault interrupter circuit breaker - US CPSCElectrical Arc Fault Detectors: AFCIs
AFCI Advice for Installers, Homeowners & Home Inspectors

  • POST a QUESTION or READ FAQs about buying, wiring, installing, & using AFCIs and the performance and about possible nuisance tripping of arc fault circuit interrupters

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Arc Fault Circuit Interrupter Information:

In this article series we define AFCI or arc fault circuit interrupter, we explain how AFCIs work, how to wire up and test an AFCI, and we discuss what goes wrong with AFCIs including nuisance tripping and AFCI product recalls. We include the electrical code requirements for AFCI installation and we cite experts who question the effectiveness and cost -effectiveness of AFCIs.

Also discussed here: Fire Problem addressed by AFCIs. Types of AFCIs & How AFCIs Work. Where to Use AFCIs & Code requirements for AFCIs. Nuisance Tripping AFCIs. How to Install AFCIs & How to Test AFCIs. AFCIs vs. GFCIs, what's the difference between an arc fault circuit interrupt or and a ground fault circuit interrupt or? AFCI Recall in 2004 & Square-D & Federal Pioneer AFCI Notice.

US CPSC Tips for installing & using AFCI's for arc fault protection to reduce fire risk in homes.

This article series includes information adapted and expanded from a US CPSC article on AFCIs, supplemented with additional details and commentary that answers most home owner and home inspector questions about installing, testing, and inspecting AFCIs - arc fault protectors in homes.

Page top photo courtesy of the US CPSC.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Electrical Arc Fault AFCI Advice for Homeowners & Home Inspectors

Arc fault circuit breaker during instsallation (C) Daniel FriedmanThis material was originally prepared by DF for the American Society of Home Inspectors New England Chapter,( ASHI -NE) Educational Seminar, Sept 22-23, 2008. Portions of this text are quoted from the Arc Fault Circuit Interrupter (AFCI) FACT SHEET provided by the US CPSC .

[Click to enlarge any image]

Additional notes and details have been added, drawing on a variety of sources listed at the end of this article.

Article Series Contents

Definition of Arc Fault Circuit Interrupter or AFCI & Definition of Arcing Faults

Arcing faults: a series arc occurs in electrical wiring when there is a small gap or break in a conductor. a parallel arc occurs when a small gap or break which permits current to flow to ground (a ground fault) or between the hot and neutral wires (a short circuit).

See Arcing Types in this article for more details.

Arcing hazards in electrical systems have long been recognized as a problem and a potential hazard dating at least to the 1920's in the U.S.[25][26] but devices to protect from arcing faults in the home are much more recent.

Arc fault circuit interrupters: an “AFCI” is an arc fault circuit interrupter first introduced in 1998.[24] AFCIs are designed to protect against fires caused by arcing faults in the home electrical wiring. [19][20] What is the actual hazard?

Arcing faults, especially parallel arcing faults, lead to overheating and a fire hazard even if no shock hazard is present. Electrical arcing faults have been described in detail by Shea who explained how electrical arcing faults can be a serious fire hazard and one that is distinct from ground faults intended to be addressed separately by GFCIs.[21][22][23]


Typical wiring details for AFCI circuit breakers

Our AFCI photo at left illustrates a Square-D 20A AFCI breaker during installation in the electrical panel.

The light green arrow points to the AFCI device - you'll notice that it is much longer than conventional circuit breakers in the panel. Each AFCI breaker involves three electrical connections:

  1. The red arrow indicates the "hot" wire connection at the AFCI breaker.
  2. The yellow arrow indicates the circuit neutral wire connection at the AFCI, and
  3. the white arrow shows that the multi-strand coiled wire from the AFCI device is connected to the neutral bus in the electrical panel.
AFCI circuit breaker connection points (C) Daniel Friedman

Our next AFCI breaker photo shows more closely the electrical circuit connection points at the AFCI breaker itself.

  1. The red arrow indicates where the "hot" wire will be connected to the uppermost screw on the AFCI breaker.
  2. The yellow arrow indicates the circuit neutral wire connection at the AFCI at the "lower" screw
  3. The white arrow shows the end of the white insulated multi-strand coiled wire from the AFCI device that will be connected to the neutral bus in the electrical panel.

The molded case of the AFCI breaker also indicates which wires should be attached to which terminals, as will instructions included with the device.

AFCI Fire Statistics: Why are AFCI's [Possibly] Important?

AFCIs are an important safety addition to homes in part because they address an additional type of electrical fault that can cause a fire and one which may not be detected and interrupted by a conventional circuit breaker, nor by a ground-fault circuit interrupter (GFCI's).

We've seen that arcing of any type can result in burned debris on wire surfaces which causes an increase in electrical resistance and thus overheating at that point. Arcing was examined earlier in detailed studies of the aluminum electrical wiring fire hazard at connections in the wire. Arcing of any type, whether it is the micro-fretting type of arcing that occurs with aluminum wire or possibly larger arcing across a gap or short in a copper wire.

The Fire Problem [intended to be addressed by AFCIs]

Electrical fire in a heater cord under a rug burned this Rhinebeck NY home (C) Daniel FriedmanAnnually, over 40,000 fires are attributed to home electrical wiring. These fires result in over 350 deaths and over 1,400
injuries each year Note 1. 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.

Our photo shows a Rhinebeck NY home that was totally destroyed by a fire caused by an electrical cord that was passed under a carpeting - a possible cause of pinched, overheated cord, and a fire that might have been prevented by an AFCI.

Certainly the circuit involved was in an older home and was not protected by an AFCI (nor by a GFCI as we understood the case). In any event the heater cord did not blow a fuse nor trip a breaker in this home. Instead it just lit the home afire.

InspectAPedia Note: According to Mike Holt, "Studies have shown that over 60 percent of fires are from causes in the fixed wiring, switches, receptacle outlets and lighting fixtures that are part of the fixed electrical system of a residence." In other words, AFCI's are focused on detecting arcing and preventing fires in an area where the risk is significant.

Arcing faults often occur in damaged or deteriorated wires and cords. Some causes of damaged and deteriorated wiring include:

and cord exposure to heat vents and sunlight.

What Types of AFCIs are Available?

UL in January 2002 described various types of AFCIs which we summarize here.[4] The first three types of AFCI's, Branch Feeder AFCIs, Outlet Circuit AFCIs, and Combination AFCIs are the three most basic types of arc fault detectors and are important definitions for the home owner or home inspector to understand:

  1. Branch Feeder AFCIs - basically a special circuit breaker to be installed in the electrical panel and which will protect all of the devices on an individual electrical branch circuit. (15A or 20A 125V single phase wiring.)
  2. Outlet circuit AFCIs - a device installed right in the branch circuit receptacle box. As with GFCIs this device may also protect wiring which is connected "downstream" electrically from the device itself.
  3. Combination AFCIs - this device combines the function of Branch Feeder AFCIs and Outlet Circuit AFCIs and will protect power cords plugged into receptacles protected by the AFCI.

    The following are additional types of AFCI's described by Underwriters Laboratories.
  4. Outlet Branch Circuit AFCIs - this device, which sounds to us just like #2 above, is installed as the first outlet in a string of electrical receptacles on a single circuit; it protects the downstream receptacles.
  5. Portable AFCIs - these devices can be plugged into a conventional electrical receptacle and provide one or more outlets into which additional devices can be connected. This device would be used by contractors working on a building to obtain additional electrical safety when using power tools.
  6. Cord-AFCIs - this device is like the portable AFCI #5 above, but may be incorporated into the permanent power cord of a device or appliance so that when it is plugged into an electrical receptacle the appliance is protected from arc faults.
  7. Leakage Current Detection and Interruption LDCIs - these devices are built into a device or appliance and detect current leakage from the device's electrical cord. If a hand held hair dryer contained this device and its damaged cord was dangled in a sink filled with water, the LDCI would detect the current leakage and would shut off the device.

How does an Arc Fault Circuit Interrupter (AFCI) Work?

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 should Arc Fault Circuit Interrupters (AFCIs) be used? Are Combination AFCI's effective?

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.

In 2008 the NEC added a requirement for AFCI protection in all living areas and also added that "only combination AFCI's are allowed". [18]

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.

Watch out: While AFCI-related patents date from as early as 1985, the current and most-widely installed AFCI designs were developed and patented by Joseph C. Engel, Robert T. Elms, & John C. Schlotterer with key patents assigned to Eaton Corporation.[17][18]

But Dr. Engel has argued that the current devices as marketed do not properly identify and address the types of electrical hazards that were addressed by his original invention. Quoting from Engel (2012) [18],

Manufacturers and UL claim that arcing across a break in a cord’s conductor is hazardous, and that a Combination AFCI will respond to prevent a fire. The author believes the claim is unproven, and will explain why the disallowed Branch/feeder AFCI provides more protection at less cost.[18]

AFCI Requirements under the US National Electrical Code NEC

InspectAPedia Notes: What are the code requirements for AFCIs?

AFCI requirements have not been adopted uniformly in all jurisdictions, but the requirement is being increasingly accepted, and we certainly recommend the use of AFCIs as described by the US CPSC and the NEC.

The US National Electrical Code, the NEC, specifies the following requirements for AFCIs (quoted indirectly from the U.S. State of Vermont office of the state fire marshal, January 2007. Vermont has required AFCIs to the NEC 2008 standard since 2000.)

History of AFCI Requirements in Homes

The 1999 NEC rules, effective in 2002, in NEC Sec. 210.12. introduced AFCI's and called for their installation on bedroom receptacle circuits powered by single phase 125V(nominal) 15A and 20A circuits.

The 2002 NEC expanded the use of AFCI's to include all bedroom circuits (such as lighting and hard-wired smoke alarms), kitchens.

The 2005 NEC code expanded the section to include combination AFCIs combined with GFCIs, basically an update to reflect improvements in the technology. The technology of AFCIs was improved to add the detection of series arcing to the previously available parallel arcing. By removing the word "receptacle" from the code in 2002, and by leaving the word "outlet" in the code, the 2005 code indicated that all outlets, including receptacles, light fixtures, smoke alarms, etc. must be protected.

The 2008 NEC expanded the use of AFCI's to include all habitable rooms in new homes such as living rooms and dining rooms. The 2008 requirements mean that only only Combination AFCI's will meet all of the requirements of the code. GFCI's (Ground Fault Circuit Interrupters) continue to be required to protect areas of high shock risk: bathrooms, kitchens, garages, un-finished basements.

Combination devices required after 1 Jan 2008: Simplifying a bit, after January 1, 2008, AFCI protection must be provided by a "Combination AFCI's" . That's because these are an improved arc fault interrupter product that offer much more sensitive arc fault detection (5 A arc peaks as opposed to 75 A arc peak detection).

210-12. Arc-Fault Circuit-Interrupter Protection (1999, Effective 2002)

(A) Definition. An arc-fault circuit interrupter is a device intended to provide protection from the effects of arc faults by recognizing the characteristics unique to arcing and by functioning to de-energize the circuit when an arc fault is detected.

(B) Dwelling Unit Bedrooms. All branch circuits that supply 125-volt, single phase, 15- and 20-ampere receptacle circuits installed in dwelling unit bedrooms shall be protected by an arc-fault circuit interrupter(s). This requirement shall become effective January 1, 2002.

Beginning with the 2008 edition of the U.S. National Electrical Code, AFCI's are required not only in bedrooms but in other areas of the home such as dining rooms, living rooms, and other habitable areas, and apply to most electrical circuits including hard-wired smoke detectors, overhead fans, etc.

2014 AFCI Arc Fault Circuit Interrupter Requirements in the U.S. National Electrical Code

Reader Comment: Current [2014 NEC] electrical code requirements for AFCI protection

2016/08/07 NHFireBear said:

Note on recent allowances and further requirements in 2014 edition of NEC for AFCI.

NFPA 70 (NEC) in the 2011 edition, section 210.12 required "combination type" protection on all AFCI circuits (i.e., all dwelling-unit living spaces except bathrooms and kitchens), but contained an exception allowing use of an outlet branch-circuit type AFCI at the first outlet in circuits properly wired using conductive conduits (EMT, MC, AC, etc) and metal boxes.

The 2014 edition specifically authorizes three additional configurations of AFCIs:

  1. BRANCH-type AFCI protection (i.e., in the panel) plus a listed OUTLET-type AFCI at the first outlet
  2. A "listed SUPPLEMENTAL arc protection circuit breaker" plus an outlet branch-circuit AFCI installed at the first outlet box"; or
  3. A listed outlet AFCI as the first outlet on the branch fed from an ordinary circuit breaker.

In the latter two cases, the wiring from the panel to the outlet-type AFCI must be "continuous", of limited distance (e.g., 70 ft for 12 AWG) and the outlet must be marked as first on the branch (unless it also qualified under the metallic branch exception).

In other words, unless the panel has a combination-type AFCI breaker for a branch requiring AFCI protection, the first outlet on the branch must ALSO be an outlet-type AFCI.

The 2014 edition [of the National Electricsl Code or NEC in the U.S. ] added a requirement for all branch circuits serving outlets in dorm rooms to have AFCI protection, as above. 210.12(C). The 2014 code also carries forward an AFCI exemption for circuits feeding fire alarm systems fed via metallic conduit to conductive outlet and junction boxes. May be worth noting that a "fire alarm system" is not the same as a "smoke alarm", or a series of interconnected smoke alarms. - NH FireBear is a fire inspector and a frequent contributor to - Ed.


Thanks NH FIreBear, for the update;

Unfortunately despite electrical code requirements for their installation as an additional measure in reduction of fire risk, AFCIs do not work so nicely as the inventors originally hoped and intended, may not do all that's promised, and in my own experience they can be so problematic that electricians I know install them just long enough to pass their electrical inspection, then they remove them and go back to standard breakers.

Electricians who have not already come across this problem should be warned, that in particular, you will have a devil of a time if you wire a building using a shared neutral for pairs of circuits where AFCIs are required by code. You will be plagued by nuisance tripping that can be remedied only by either eschewing the AFCIs OR by a complete re-wiring to provide separate neutral conductors.


Current Limits of Protection of combination AFCI devices as sold & installed

Reader Question/Comment: Combination AFCIs' what they will and will not do - article by Engel

You and your readers should take a look at Combination AFCIs" What they Will and Will Not Do - [PDF] an IEEE publication available for public non-commercial use - Steve 1/31/2013


Repeating Steve's suggestion 1/31/13 that we read Joe Engel's paper on Combination AFCIs, we contacted Mr. Engel as well, and appreciate your contribution of a publicly-available copy of this important paper. Indeed thanks to a pointer from Dr. Jess Aronstein, we contacted Dr. Engel and have discussed AFCI issues by private email. I was concerned that his article was not available for free to the public, as it appeared in an IEEE publication. However both reader Steve and Dr. Engel have provided links to this document.

In the references section to this article as well as immediately below we include a reference and link to Dr. Engel's critical article about combination AFCIs and their capability.

Joseph C. Engel, PhD., IEEE, "Combination AFCIs" What they Will and Will Not Do", [PDF] 19th Annual IEEE IAS Electrical Safety Workshop, Daytona Beach, Jan/Feb 2012.

My understanding of a fundamental concern is that as presently mandated, defined, manufactured and marketed, AFCIs do not provide the protection that was the original intent of Dr. Engel [17] as he has made amply clear [18].

Below are excerpts from the conclusion of this important article:

The primary goal of this paper was to describe what a Combination AFCI circuit breaker can do, while also clarifying what it can’t do. The features of the Combination AFCI, and the earlier Branch/feeder AFCI [... ] Neither provides series arc protection, the Branch/feeder provides the extra important feature of 30mA ground fault protection.

The paper goes on to explain, but not justify, how the Combination AFCI came to be mandated, while the Branch/feeder that provides more protection at less cost is disallowed. The key drivers behind this were the AFCI manufacturers, their NEMA organization, and UL.

The author hopes this paper will stir discussions amongst the principals and correct any errors that were made concerning their products’ performance. This would also include supporting removing the Combination AFCI mandate from the NATIONAL ELECTRICAL CODE (NFPA 70).

Finally, the author, having participating actively during the AFCI development, would encourage the IEEE engineering communities of these great institutions to become more engaged to insure their codes and standards representatives fully understand the technical issues. These are their products; they have a responsibility to insure their products are not inadvertently misrepresented.

Reader Question: Electrician complains of nuisance tripping and AFCI failure-to trip

I'm still asking how these AFCI devices became code prior to it being available on the market and proven effective. To date I have encountered false tripping from these devices where a HO was nearly overcome from fumes from bedroom gas fireplace, other nuisance tripping from TVs, Vacuums, Hair dryers.

I have a picture of one of these breakers with a molten branch circuit conductor emanating from a loose connection on the AFCI breaker itself, another report of a fire that started in a ceiling fan box where the AFCI also failed to trip. These devices are absolute garbage made code by the manufacturers on the NFPA to boost revenue. Somebody here show me some proof of them actually preventing a fire other that remaining on and tripping for sudden loads from appliances. - Honest Electrician 9/3/2011


Honest, you should contact the US CPSC directly to make your concerns known. We publish studies and field reports on various electrical hazards but have no financial interest in the sale of any products or services.

InspectAPedia is an independent publisher of building, environmental, and forensic inspection, diagnosis, and repair information provided free to the public - we have no business nor financial connection with any manufacturer or service provider discussed at our website.

Watch out: also See NUISANCE TRIPPING of AFCIs

How Much Does an AFCI Cost? Cost Benefit Calculation of AFCI's:

An AFCI circuit breaker typically costs about $30. to $35. U.S. A conventional 15A circuit breaker typically costs $2. to $4. There is an additional cost to install an AFCI circuit breaker, but as it's basically a "plug-in" device that is placed in the electrical panel, that number should be small, smaller still if the AFCI installation is combined with other electrical work needed at a home.

While these specialized AFCI circuit breakers cost more, our opinion is that this is not a significant cost compared with the value of a home, not to mention the more difficult to measure cost of possible injuries or fatalities should a fire occur.

If we use the current (2014) median price of a new home in the U.S. of about $260,000., the cost of adding AFCI to a home circuit is less than two ten-thousandths of the cost of the home. (An AFCI costs 0.00016 x median value of a home in the U.S.).

If a home needs a dozen AFCI's to meet the 2008 NEC, the cost should be less than $400., or less than two thousandths of the cost of the home. (0.0019 x the median value of a home in the U.S.).

Nuisance Tripping of AFCI's - AFCI breakers trip off due to crosstalk

This discussion has moved to a separate article: See NUISANCE TRIPPING of AFCIs

How to Install an Arc Fault Circuit Interrupter (AFCI)

AFCI wiring hookup diagramPlease see this information now in a separate article at HOW TO INSTALL & TEST AFCIs. AFCI circuit breakers should be installed by a qualified electrician. The installer should follow the instructions accompanying the device and the panel box.

How to Test an Arc Fault Circuit Interrupter (AFCI)


AFCIs vs. GFCIs: What is the difference between an Arc Fault Circuit Interrupter and a Ground Fault Circuit Interrupter?

See AFCIs vs. GFCIs

2008 Code Changes Affecting Ground Fault Circuit Interrupters GFCI's

This text is now found at GFCI PROTECTION, GFCI CODES

AFCI Square D Arc Fault Circuit Breaker Recall

In 2004 Schneider Electric issued a recall of early model Square D® AFCIs. Details are at AFCI RECALL in 2004

How to Report an AFCI or other Electrical or Product Failures or Incidents to the U.S. CPSC

Please use the CPSC form found at

To comment on or suggest additions to this article use the Comments Box found below, or use our email found at CONTACT


Continue reading at AFCI GFCI TESTING & SAFETY or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.




Or see this

Article Series Contents

Suggested citation for this web page

AFCIs ARC FAULT CIRCUIT INTERRUPTERS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia


Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

HTML Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher's Google+ Page by Daniel Friedman