.................... 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.

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.


Limitations
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.