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This article, based on a US CPSC article and supplemented with additional details and commentary answers most home owner and home inspector questions about installing, testing, and inspecting AFCIs - arc fault protectors in homes. Readers of this article should also see Electrical Code Basics and SAFETY FOR ELECTRICAL INSPECTORS. ASHI Home Inspector Educational Seminar Proceedings: ASHI-NE Chapter Annual conference This website provides information about a variety of electrical hazards in buildings, with articles focused on the inspection, detection, and reporting of electrical hazards and on proper electrical repair methods for unsafe electrical conditions. Critique and content suggestions are invited. Page top photo courtesy of the US CPSC. Credit is given to content editors and contributors. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website. The AFCI arc fault circuit breaker photo at page top courtesy of the US CPSC whose consumer advice is reported below. Electrical Arc Fault AFCI Advice for Homeowners & Home InspectorsThis material was originally prepared 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 . Additional notes and details have been added, drawing on a variety of sources listed at the end of this article. What is an Arc Fault Circuit Interrupter or AFCI? The “AFCI” is an arc fault circuit
interrupter. AFCIs are newly-developed
electrical devices designed to protect InspectAPedia Note: 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). Arcing faults, especially parallel arcing faults, lead to overheating and a fire hazard even if no shock hazard is present. 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 [addressed by AFCIs]
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. InspectAPedia Note: What Types of AFCIs are Available?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:
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 Where should Arc Fault Circuit Interrupters (AFCIs) 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 InspectAPedia Notes: What are the code requirements for AFCIs?
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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. An AFCI hookup wiring diagrams and detailed instructions from GE is available here. Other manufacturer's Arc Fault Interrupter installation guidelines will be similar. Typically for an electrical circuit to be protected by AFCI, in the electrical panel the circuit hot and neutral wires are connected to marked terminals on the AFCI circuit breaker and a third wire connects the AFCI breaker to the neutral bus in the electrical panel. The AFCI installation wiring diagram shown here and others are available from GE, General Electric Corporation and GE circuit breaker distributors. |
 Safety Warning: Do not attempt to work on your electrical wiring, switches, or outlets unless you are properly trained and equipped to do so. Electrical components in a building can easily cause an electrical shock, burn, or even death. Even when a hot line switch is off, one terminal on the switch is still connected to the power source. Before doing any work on the switch, the power source must be turned off by setting a circuit breaker to OFF or removing a fuse. See SAFETY FOR ELECTRICAL INSPECTORS and Electrical Wiring Books & Guides |
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.
Because it has been misunderstood and criticized it's worth noting that the test button on an AFCI does not simply force the mechanical internal switch of the AFCI to trip. Rather, the test button on an AFCI tests the arc fault detection circuitry to be sure that it is working properly, that it will respond to an arc fault, and that the circuitry will in turn cause the mechanical internal switch to open.
This is an important distinction to remember, since the Ground Fault Circuit Interrupter (GFCI) has faced similar criticism. We've certainly found lots of GFCI's which exhibited an error when the GFCI test button was pressed: the button caused the GFCI to trip but the device was defective or improperly wired so that it would not protect the circuit.
As of September 2008 we have found no test tool that reliably and completely tests the function of an AFCI. Only the integral test button tests the circuitry of the device as well as the trip mechanism. UL classes these "test" devices not as "testers", but as "indicators".
A problem is that some devices used to "inspect" an AFCI, in trying to produce a simulated arc fault condition, may fail to cause the AFCI device to trip even though it is perfectly fine.
Literature from the manufacturer of a popular "test tool" tells the user of the tool to go to the electric panel and use the test button on the AFCI device to make sure it trips. In other words the inspector cannot rely on the separate test tool. For this reason you will see such tools referred to as "indicators" rather than "testers": they are not a complete and reliable test instrument for AFCIs. -- Mike Holt
What is the difference between an AFCI Arc Fault Circuit Interrupter and a GFCI Ground Fault Circuit Interrupter? The AFCI should not be confused with the GFCI or ground fault circuit interrupter.
An AFCI is a device intended to prevent a fire. It detects a type of arcing in the electrical circuit that can lead to overheating and a fire. An AFCI can protect against some types of shock by detecting a short circuit if the short is also affecting an individual, but it is not designed as a shock protector and will not detect all of the same faults as a GFCI.
A GFCI is a device intended to prevent electrical shock. A GFCI will not necessarily detect the type of electrical arcing that can cause a fire. 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.
InspectAPedia Note: don't confuse this "combination" with the "Combination AFCI described earlier in this article.
While we're discussing the 2008 electrical code changes for AFCI's let's also update ourselves about GFCI's:
NEC 210.8 is the code section pertaining to GFCI's. (AFCI's are addressed in NEC 210.12.). These GFCI requirements are intended to address residential electrical wiring using 15A or 20A 120V electrical receptacles and circuits. Heavier-duty circuits such as a 30A welder circuit are excluded.
Basically GFCI protection requirements have been expanded to all basement, garage, and accessory building receptacles, and a wording change to drop "receptacles" and keep "outlets" expands GFCI coverage in other areas.
For 2008 the NEC deleted Nos. 1 and 2 to 210.8(A)(2) and Nos. 1 and 2 to 210.8(A)(5) from the prior NEC version.
210.8(A)(2) & (A)(5): Expanded GFCI protection requirements by deleting exceptions for receptacles that are not readily accessible and receptacles located in dedicated spaces to supply an appliance.
Deleting "receptacle" and leaving "outlet" in the NEC expands the required coverage of any device being discussed. That's because a "receptacle" is taken to mean an electrical outlet (a wall socket) while "outlet" is any place in the electrical wiring system from which electrical power is taken (a ceiling fan, a hard-wired smoke detector, etc.).
• 210.8(B)(4): Expanded GFCI protection requirements to include all outdoor 15- and 20-ampere, 125-volt receptacles, and added a conditional exception to permit use of assured equipment grounding conductor program in industrial establishments.• 210.8(B)(5): Added GFCI protection requirements for all 15- and 20-ampere 125-volt receptacles installed within 6 ft of the outside edge of sinks, and added exceptions for receptacles in industrial laboratories where the loss of power would introduce a greater hazard and for receptacles in patient care areas where critical care equipment may be utilized.
Basement GFCI changes: The GFCI protection requirements for receptacles in basements, garages, and accessory buildings have been expanded to all 125-volt, single-phase, 15- and 20-ampere receptacles regardless of accessibility or movability of an appliance from one location to another. - Minnesota Electrical Association
GFCI's are required safety devices to be installed in the following locations:
In 2004 Schneider Electric issued a recall of early model Square D® AFCIs manufactured between March 1 2004 and September 23, 2004 because tests indicated that "... arc detection in these breakers may become inoperable due to an issue with a third party-supplied internal component in the electronic detection unit."
Schneider's letter emphasized in an opening statement that "... Square D Company, the leading manufacturer of electrical equipment, is committed to the safety of our people, our customers, and our products." The company's letter provided additional detail:
While these circuit breakers will continue to function normally, providing short-circuit and overload protection, a small percentage of the breakers may not function as an arc fault circuit breaker (AFCI) and detect a high-resistance low-current arc fault. The unique role of an AFCI is its ability to detect an electrical arc and shut down a circuit before a fire can start or spread. It is important to note that the affected circuit breaker itself does not pose a hazard.
[The company was concerned about inaccurate and misleading information in the electrical products market and asked that concerned parties turn to them for information regarding their products, including AFCIs.]
The positive responses we have received from electrical inspectors regarding our honest and direct approach to resolving this issue have been appreciated. Many inspectors have been working actively with us as well as their local electrical contractors and builders to minimize the disruption in the construction process. Those combined efforts have been successful at a vast number of localities.
[...]
We believe that we can accept nothing less than excellence when it comes to safety. For more than 100 years, our customers have associated the Square D brand with industry leadership, safety, quality, and reliability. We intend that our efforts through this AFCI program will continue those qualities.
Particular thanks are due to experts and also consumers who read these articles and suggest corrections, changes, and additions to the material. Content suggestions, technical corrections and content critique are invited for any of the content at our website.
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.
The 2008 NEC National Electrical Code (ISBN 978-0877657903) Online Access LINK (you'll need to sign in as a professional or as a visitor)
GE, General Electric Corporation, General Electric Company, 41 Woodford Ave., Plainville, CT 06062, one of the companies producing AFCIs, provides wiring diagrams and installation instructions for their product. See GE's DEH-40117R4.pdf for detailed installation instructions from GE for the wiring of a typical AFCI on a simple 120V home electrical circuit.
The Minnesota Electrical Association has posted an article of the most important electrical code changes for 2008 at http://www.electricalassociation.com/catalog/2008NECTop10.aspx - by Michael J. Johnston, IAEI
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