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.
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.
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This 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.
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. 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. AFCIs are designed to protect against fires caused by arcing faults in the home electrical wiring.  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.
Also see AFCI GFCI TESTING & SAFETY
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:
Our next AFCI breaker photo shows more closely the electrical circuit connection points at the AFCI breaker itself.
The molded case of the AFCI breaker also indicates which wires should be attached to which terminals, as will instructions included with the device.
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.
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 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.
UL in January 2002 described various types of AFCIs which we summarize here. 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:
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.
In 2008 the NEC added a requirement for AFCI protection in all living areas and also added that "only combination AFCI's are allowed". 
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
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.
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) ,
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.
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.)
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.
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:
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 InspectApedia.com - 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.
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  as he has made amply clear .
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.
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
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.).
This discussion has moved to a separate article: see NUISANCE TRIPPING of AFCIs
Please 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.
Please see HOW TO INSTALL & TEST AFCIs
See AFCIs vs. GFCIs
This text is now found at GFCI PROTECTION, GFCI CODES
In 2004 Schneider Electric issued a recall of early model Square D® AFCIs. Details are at AFCI RECALL in 2004
Please use the CPSC form found at https://www.saferproducts.gov/CPSRMSPublic/Incidents/ReportIncident.aspx
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This does not address grandfathering for homes older than 2008! - John, 7/24/2011
Granfathering and the AFCI requirement: good point, John. We find a variety of opinions among building code officials. At a recent building addition project the BCO wanted AFCIs in the new sub panel in keeping with the new electrical code AFCI recommendations, but he also decided that other areas in the home needed certain updates too.
Other electrical inspectors and building code inspectors look only at the new work - I'd say that's the most common case. Only when an older home is being renovated to include electrical work will most inspectors call for current codes to be complied-with.
A more subtle exception occurs in the case of egregious electrical hazards: when an older home is being purchased, some lenders and some insurance companies may require certain updates such as in panel ampacity or in replacement of some of the more troublesome brands (FPE Stab-Lok is an example.)
do you have to use arc fault on lighting only circuits? - Hugh Owen 8/22/2011
Yes. On the illustrations I've seen the overhead lighting circuits were included. see 210.12(B) Dwelling Units - quoting the Minnesota Electrical Association reference found at the bottom of this article:
Combination-type AFCI-protective devices are now required in all dwelling unit rooms, except for kitchens, bathroom, garages, basements, and rooms or areas not specified in this section. This continues the incremental migration to provide whole-house AFCI protection for dwelling units that was the objective of the original proposals in the 1999 NEC development cycle.
This section was revised to include a list of rooms and areas where the serving branch circuits are to be protected by arc-fault circuit-interrupter protection. Essentially, the requirements for this protection are expanded to most areas and rooms in the dwelling unit with the exception of those named above and other areas or rooms not specifically identified in this section. The AFCI-protective devices must be listed combination types.
I don't have space in the panel to make proper ground bus connections. - Roger 9/11/11
Roger, as long as your panel won't be overcrowded, you can always add an additional ground bar (or neutral bar) in the existing panel, connecting it to the originals and locating it where your AFCI white wire will reach.
I have a Sylvania main breaker panel in an existing dwelling. I am adding 3 circuits to basement finish.
Inspector wants a Listed product for the panel . Any idea what AFCI breaker I can use? - Nice Article 12/10/11
Any AFCI breaker sold at any electrical supplier will be code compliant. Just how well the product works is a different issue as discussed in this article. Be sure to see the comments and links to Dr. Engel's paper given in FAQs. below.
How to deal with 14-3 wired rooms. I need AFCI for the outlets and the lighting, I have wired 14-3 and would need a special AFCI that doesn't seem to be offered by Square D. - Eric J 5/22/2012
You raise an important question: how to use AFCIs or GFCI's on 3-wire circuits. I don't know a solution and so far the solution certainly is not offered in the device itself. We have ongoing reports as well as direct experience with nuisance tripping and so unreliable behavior when AFCIs or GFCI's are installed on shared-neutral circuits. The electrician I worked with most recently says he's changed is policy and won't install 3-wire shared neutral circuits where an AFCI or GFCI is going to be required.
In sum, AFCI's are NOT going to work properly on shared-neutral electrical circuits; neither do GFCIs.
I have two Seimen's AFCIs for 3 bedrooms. They were placed approx spring 2004 in a new build. No problems until several months ago with LED TV in master bedroom. Breaker would trip upon trying to turn on tv on rare occasion. At first seemed overload but now it trips every time TV is turned on.
TV is tripping the other AFCI in the other bedrooms as well. It IS NOT tripping the standard breakers elsewhere in the house. Are these older model AFCIs needing replaced to handle the load of the new appliances? Have new breakers become more reliable as stated above at avoiding nuisance tripping (which I assume this is)? - Kathy 8/20/2012
You are reporting nuisance tripping.
You should also contact the US CPSC directly to make your concerns known. Use this US CPSC Incident Report Form to report Zinsco or Sylvania-Zinsco equipment failures and problems. Please also report incidents to this web author.
i have ham radio equipment
the AFCI is reading the fluctuating current demands as arching. breaker constantly trips. this is a pain! can i safely replace the afci with a standard breaker? - Paul 8/23/2013
Paul this sounds like another instance of nuisance tripping. You can replace the AFCI with a standard breaker and stop the tripping problem; you will be giving up what limited added safety protection the AFCI offered, and you could face a technical issue with your local electrical inspector.
You should also contact the US CPSC directly to make your concerns known. Use this US CPSC Incident Report Form to report Zinsco or Sylvania-Zinsco equipment failures and problems.
Please also report incidents to this web author.
DanJoeFriedman (mod) said:
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. In the article above we include a reference and link to
Joseph C. Engel, PhD., IEEE, "Combination AFCIs" What they Will and Will Not Do", IEEE, 2012
(Sept 2, 2011) Honest Electrician said:
How much money has been paid to the NFPA to make AFCI breakers code since there have been arc outs and fires on protected circuits and they were introduced as code before they were available
(Sept 19, 2014) Mike said:
Can a AFCI be used to protect Alum branch wire circuits
Yes, and no.
yes if the AFCI is connected using CPSC-recommended methods (AMP TYCO COPALUM or the King Innovations AlumiConn) to connect the device to the circuit
No if you are thinking of direct-wiring the device to the aluminum wire. I have personally seen an aluminum wired test circuit overheat and begin to burn (we turned off power at that point) while powered through an AFCI.
Your US CPC Incident report form link is obsolete. Here's the new link:
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 To paraphrase the article, there is no such thing as an AFCI tester, other than the test button that is an integral part of the AFCI device itself. The reason for this is that an AFCI device is very complex, and recognizes the actual waveform of an arcing fault. While the advertised "AFCI Testers" do produce a waveform similar to that of an arc fault, they cannot produce an actual arc fault. Because of this, the "tester" may not trip the AFCI circuit breaker, despite the breaker having nothing wrong with it. For this reason, UL classifies these devices not as "testers", but as "indicators", which is much more accurate.
 These devices are tested under the UL 1436 standard, and are required to have included in the instructions the following clause (or equivalent):
"CAUTION: AFCIs recognize characteristics unique to arcing, and AFCI indicators produce characteristics that mimic some forms of arcing. Because of this the indicator may give a false indication that the AFCI is not functioning properly. If this occurs, recheck the operation of the AFCI using the test and reset buttons. The AFCI button test function will demonstrate proper operation."
 While these indicators may have some value for convenience to determine if the outlet in question is on an AFCI protected circuit, they are not to be substituted for the test button of the AFCI circuit breaker, and they are not an AFCI tester.