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Arc Fault Breaker


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AFCI Fact Sheet

Arc-fault circuit Breaker
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. Arc faults 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.

Starting with the 1999 version of the National Electrical Code (NEC, also called NFPA 70) in the United States and the 2002 version of the Canadian Electrical Code in Canada (CSA Standard C22.1), the national codes require AFCIs in all circuits that feed receptacles in bedrooms of dwelling units. This requirement is typically accomplished by using a kind of circuit-breaker (defined by UL 1699) in the breaker panel that provides combined arc-fault and overcurrent protection. Not all U.S.A. jurisdictions have adopted the AFCI requirements of the NEC as written.

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 (note: the Canadian Electrical Code uses different terminology but similar technical requirements). 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 against

1. 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

In 2002, the NEC removed the word "receptacle" leaving "outlets", in effect adding lights within dwelling bedrooms to the requirement [debated interpretation]. The 2005 code made it more clear that all outlets must be protected, despite code making panel discussion about excluding bedroom smoke detectors from the requirement. "Outlets" is defined in "Article 100 Definitions" of the NEC as "A point on the wiring system where current is taken to supply utilization equipment" and this includes receptacles, light fixtures, and smoke alarms, among other things.

As of January 2008, only "combination type" AFCIs will meet the NEC requirement. The 2008 NEC requires installation of combination-type AFCIs in all 15 and 20 ampere residential circuits with the exception of laundries, kitchens, bathrooms, garages, and unfinished basements.

AFCIs are designed to protect against fires caused by electrical arcing faults. However, they provide no specific protection against "glowing" connections, excess current, high line voltages, or low line voltages. For descriptions of electrical fire causes, see "How Electricity Starts Fires", John S Robison, P.E., Electrical Line magazine, November / December 2007 issue, pages 60–70 (; NFPA 921 "Guide for Fire and Explosion Investigations", 2004 edition; and "Ignition Handbook", Dr. Vytenis Babrauskas, Fire Science Publishers, 2003.

Glowing connections occur when relatively high electric current exists in a relatively large resistance. Heat comes from power dissipation. Power (in watts, symbol W) equals the current (in amperes, symbol A) squared, multiplied by the resistance (in ohms, symbol Ω). For example, a 60 watt lamp operating on a 120 V circuit draws 1/2 ampere of current. An 1800 watt space heater on a 120 V circuit draws up to 15 amperes. If a bad wiring junction in a circuit has a resistance of 1 ohm, then a 60 W lamp will cause it to dissipate 0.25 watt of power (0.5 A * 0.5 A * 1 Ω). In contrast, an 1800 W heater could theoretically cause the bad wiring junction to dissipate 178 watts (13 A * 13 A * 1 Ω). Note that the current is less than 15 A because of the combined resistance of the heater plus the bad wiring junction. This energy, dissipated in a small junction area, can generate temperatures above 1000 degrees Celsius. Those temperatures can ignite most flammable materials. Bad wiring junctions can occur in utilization equipment, cords, or premise wiring (especially in defective switch, socket, plug, or wire connection, even at circuit breaker or fuse panels). High resistance junctions are commonly observed in improperly terminated aluminum wire junctions. No technology located in a circuit breaker or fuse panel could detect a high-resistance wiring fault, as no measurable characteristic exists that differentiates a glow fault from normal branch circuit operation. Power Fault Circuit Interrupters (PFCI) located in receptacles are designed to prevent fires caused by glowing connections in premise wiring or panels. From the receptacle, a PFCI can detect the voltage drop when high current exists in a high resistance junction. In a properly designed circuit, substantial voltage drops should never occur. Proper wire terminations inside utilization equipment (e.g. appliances, lamps, heaters) and cords prevent high-resistance connections that can lead to fires.

Excess current can heat entire lengths of wire. Thermal circuit breakers are designed to protect against excess current through the permanent circuit wiring. However, excess current through the smaller wires in utilization equipment can exist, at levels below the trip thresholds of a circuit breaker. Overload fault circuit interrupters (OFCI) are designed to protect against excess current drawn by utilization equipment. OFCIs must be located within receptacles. Both thermal circuit breakers and OFCIs are required to prevent fire ignition from excess current.

High line-voltage creates excess power and heat in utilization devices such as heaters, light bulbs, appliances, motors, and electronics. In extreme cases, this heat can ignite fires. One extreme source of high line voltage occurs from a neutral path opening within a two-leg 120 V residential electrical system. When a neutral wire breaks or opens, the utilization voltage can almost double to over 200 V with large leg-to-leg load imbalances. This extreme situation can result in almost four times the power and heat in loads. With such overheating, some loads can reach self-ignition temperature in less than 10 minutes. Power fault circuit interrupters (PFCIs) are designed to prevent fires caused by excess voltage across loads. Voltage-trip circuit breakers detect excess line voltages, but are unable to detect sub-circuit open neutral conditions.

Low line voltage can cause electro-mechanical relays (on-off switches) to repeatedly turn off (relay opens) and on (relay closes again). If current is flowing through the load contacts, it will cause arcing across the contacts when they open. The arcing can oxidize, pit and melt the contacts. This process can increase the contact resistance, superheat the relay and lead to fires. Power fault circuit interrupters are designed to prevent fires from low voltage across loads.

New Electrical Code Requirements as of The 2008 National Electrical Code

2008 NEC—210.12

Arc-Fault Circuit-Interrupter Protection.

(B) Dwelling Units. All 120-volt, single phase, 15- and 20-ampere branch circuits supplying outlets installed in dwelling unit in family rooms, dining rooms, living rooms, parlors, libraries, dens, sun rooms, recreation rooms, closets, hallways, or similar rooms or areas shall be protected by a listed arc-fault circuit interrupter, combination type installed to provide protection of the branch circuit.

FPN: For information on types of arc-fault circuit interrupters, see UL 1699-1999, Standard for Arc-Fault Circuit Interrupters.

Exception No. 1: Where RMC. IMC, EMT or steel armored cable, Type AC, meeting the requirements of 250.118 using metal outlet and junction boxes is installed for the portion of the branch circuit between the branch circuit overcurrent device and the first outlet, it shall be permitted to install a combination AFCI at the first outlet to provide protection for the remaining portion of the branch circuit.

The action in these proposals deleted the phrase “supplying outlets” and the word “bedrooms” now requiring AFCI protection for all 120-volt, single-phase, 15- and 20-ampere branch circuits in family rooms, dining rooms, living rooms, parlors, libraries, dens, sun rooms, recreation rooms, closets, hallways, or similar rooms or areas. In addition, the last sentence, permitting branch/feeder AFCI devices until January 1, 2008, has been deleted, and the effect is to now require only listed combination AFCI branch circuit protection.

A new exception has been added permitting RMC, IMC, EMT or steel AC cable to protect the branch circuit to the first outlet with the 6-foot length deleted.

Award-Winning Combination Type Arc Fault Circuit Interrupter from Siemens is Now Available

Meets requirements of National Electrical Code® update effective Jan. 1, 2008

ATLANTA -- Siemens Energy & Automation, Inc. today announced that its full residential line of award-winning Combination Type Arc Fault Circuit Interrupters (AFCIs) is now available. Recently named "Equipment of the Year" by Independent Electrical Contractors (IEC), Siemens' AFCIs meet all requirements of the current and proposed codes. The Combination Type AFCIs have been listed by Underwriters Laboratories Inc. (UL®) and are available for use on 120-volt, single-phase, 15- and 20-ampere branch circuits.

The new Combination Type AFCI device is equipped with Siemens patented unique LED trip indicators, which will help electricians and home owners pinpoint the type of problems that may cause the device to trip. The LEDs located near the handle of the circuit breaker can distinguish whether the trip was caused by arcing faults, arcing to ground or over current conditions.

"Arc faults are extremely dangerous because they generally occur in wiring that is behind drywall or in attics, going undetected until a fire breaks out, which is why Siemens has been investing in research and development and partnering with industry innovators to develop arc fault technology," said Dennis Sadlowksi, president and CEO of Siemens Energy & Automation. "Siemens ability to be the first to market with the Combination Type AFCI technology is a testament to our commitment to providing our customers with the latest and most advanced technology."

Siemens Combination Type AFCI device is the most compact on the market. As a result, it is retrofitable for all Siemens, Murray, I-T-E, and Crouse-Hinds load centers and meter load center combinations. Additionally, Siemens "INSTAWIRE(TM)" feature included in all Siemens load centers saves time during installation.

Combination Type AFCIs, which protect against all three possible types of arc fault, improve on the protection offered by the branch/feeder AFCIs currently permitted by the 1999-2002 NEC®, as well as the 2005 NEC®, until January 1, 2008. Branch/feeder AFCIs protect only against line-to-ground and line-to-neutral arcs, known as parallel or high-energy arcs.

Combination Type AFCIs, which will be required by 2005-2008 NEC starting Jan. 1, 2008, protect against both of these arc faults plus series arcs, which can be caused by broken conductors, loose screws and a host of other invisible faults.

The arc fault circuit breakers is intended to prevent fire from arcs to ground and works at a higher threshold (30 mA) than the GFCI/RCD (Ground-Fault Circuit Interrupt/Residual-Current Device) implementations protecting against the safety hazard of electric shock (which operate at 6 mA). However, advanced electronics inside an arc fault circuit breakers breaker detect sudden bursts of electrical current in milliseconds, long before they would trip a regular overcurrent circuit breaker or fuse. Combined devices are available which trip at the lower, 6 mA threshold of a true GFCI/RCD.

In 2002, the NEC removed the word "receptacle" leaving "outlets", in effect adding lights within dwelling bedrooms to the requirement [debated interpretation]. The 2005 code made it more clear that all outlets must be protected, despite code making panel discussion about excluding bedroom smoke detectors from the requirement.

Beginning Jan 2008, only "combination type" arc fault circuit breakers' will meet the NEC requirement. These can protect cords as well as wiring.

Even arc fault circuit breakers, however, do not provide protection against all of the possible circuit faults that could ignite a fire. In particular, they provide no special protection against so-called "glow faults" where a relatively low-resistance short circuit draws a modest amount of current (within the trip limits of the circuit breaker) but heats the localized area of the fault to red heat. Glow faults also can occur where a connection in series with a load suddenly develops a high resistance; this might be the result of a now-defective switch, socket, plug, or wire connection (series faults are also commonly observed in aluminum wire junctions). No practical circuit breaker could detect either such fault as there is no measurable characteristic that any circuit breaker could employ to distinguish a glow fault from the normal operation of a branch circuit.



The US Consumer Produce Safety Commission states “Problems in home wiring, like arcing and sparking, are associated with more than 40,000 home fires each year. These fires claim over 350 lives and injure 1,400 victims annually. Their position on Arc fault circuit breakers can be found at The CPSC has data sheets on Arc fault circuit breakers at



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