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Arc Fault Detection: Your Questions Answered

Nov. 1, 2007
The National Electrical Code (NEC) requirements for arc fault circuit interrupters (AFCIs) have become more stringent with each passing Code cycle, stirring up much discussion and debate among builders, electrical contractors, and other professionals involved in home construction. While these devices were previously only required to protect the bedroom, the 2008 NEC now requires the technology to

The National Electrical Code (NEC) requirements for arc fault circuit interrupters (AFCIs) have become more stringent with each passing Code cycle, stirring up much discussion and debate among builders, electrical contractors, and other professionals involved in home construction. While these devices were previously only required to protect the bedroom, the 2008 NEC now requires the technology to be installed in additional areas of the home, including dining rooms, living rooms, and other habitable areas.

Many prominent experts in the electrical and homebuilding communities believe this expanded requirement will have a significant positive impact on homeowner safety (see the Figure), reducing the number of lives lost and injuries that occur in home electrical fires. According to a 2006 report from the United States Fire Administration, approximately 67,800 fires occur annually due to problems in a home's electrical system, resulting in approximately 485 deaths, more than 2,300 injuries, and more than $868 million in residential property loss.

Not all experts and end-users agree with this line of thinking, however. Some have argued that the cost of the AFCI is higher than standard circuit breakers and, as such, cost too much to be in balance with the increased protection. Others have argued that because it is a relatively new type of protection device, the AFCI does not have the history on which to base a decision about whether to support it or not. As with most new technology developments, questions and concerns covering a variety of issues exist. Since AFCI inclusion in the NEC, questions have arisen, ranging from cost and availability to nuisance tripping and the experience level among those responsible for AFCI installation.

This article will explore some of these important questions and attempt to clear up some misconceptions that may be circulating in the industry.

Cost vs. benefit

One of the more popular questions regarding AFCIs and the expanded Code requirements for their installation is whether the additional cost is worth the benefits the technology provides to the homeowner.

While AFCIs have been a part of the NEC since the 1999 edition (see The Evolution to Develop Arc Fault Technology below), some states and municipalities have removed the AFCI requirement from the Code during their own Code-adoption process, citing cost as a key factor. On the flip side, Vermont has been requiring AFCIs since 2000. In fact, the state already requires AFCIs to be installed in the rooms outlined in the 2008 NEC.

While there is an added expense associated with equipping a home with AFCIs instead of standard circuit breakers, safety advocacy groups and other AFCI supporters believe that the benefits significantly outweigh the cost (see United Front below), arguing that the cost is relatively insignificant when measured against the number of deaths and injuries that may be prevented.

A quick survey conducted by the National Electrical Manufacturers Association (NEMA), Rosslyn, Va., of hardware stores and “do-it-yourself” home centers found AFCIs priced in the $30 to $35 range, and standard circuit breakers costing between $2 and $4. As the average number of circuits in a home requiring AFCIs is 12, this equates to an approximate cost increase of $372 to $396, approximately one-fifth of 1% of the national average cost of a 2,500-square-foot home. (Note: These figures do not include installation costs.)

To trip or not to trip

Another argument against the use of AFCIs is over the issue of nuisance tripping. However, consistent findings throughout the AFCI implementation process have revealed that the majority of the nuisance trip issues are related to installation problems — specifically the wiring practices of some electricians. Specific examples include reversing neutral and ground wires, shared neutral wiring on single-pole circuits, and ground wires touching neutral wires.

Electrical contractors have been very active in providing information about these types of wiring problems. Many contractors indicate that the initial installation issues associated with wiring errors have disappeared as the installers become more familiar with the installation and operation of AFCIs.

One common misconception is that AFCIs are not tested for nuisance tripping on real-world products and circuits. Between all of the AFCI manufacturers' products, there are now millions of operating hours with AFCIs (both in field tests and in new and existing homes) that showcase the successful performance of AFCIs in protecting new and old appliances. These tests include the new combination AFCI.

Manufacturers contend that the same concern existed in the 1999 NEC, when the branch/feeder AFCI was first introduced. Louder voices were heard when GFCI provisions were expanded to commercial kitchen outlets in the 2002 NEC. Those claims proved to be unfounded, and manufacturers are confident that combination AFCIs will prove to be successful when properly installed.

The experience factor

Opponents of the expanded NEC requirements for AFCIs suggest that there may be a lack of experience among electrical contractors in using the combination-type AFCI. Some have argued that this may pose a major problem while others believe it isn't a factor at all.

Whether it's the branch/feeder type or the newly required combination-type AFCI, installation is essentially the same. The difference is in product performance. Combination-type AFCIs detect not only parallel arcing, but also series arcing, which is useful in lower-level arcing conditions.

Testing 1, 2, 3

As the AFCI has evolved, it has become clear that the purpose and operation of the TEST button on AFCIs has been misunderstood. The myth stems from the belief that it is simply a mechanical tripping device to the misconception that the button tests the entire branch circuit.

The TEST button on the AFCI is required to comply with UL 1699 — the recognized national standard for AFCIs. UL 1699 covers a wide variety of conditions that may affect AFCI performance, including humidity, unwanted tripping, abnormal operation, voltage surges, and more.

The TEST button is designed to test the function of the electronics of the AFCI to ensure that the detection circuitry is working properly, which, in turn, triggers the mechanical operation of the device. A successful trip verifies that the device is continuing to monitor the entire branch circuit for arcing conditions.

Are combos available?

Now that the 2008 NEC has been approved and published, some in the industry are concerned about the availability of the combination-type AFCI. While the 2008 NEC expands the use of this type of breaker, manufacturers don't foresee availability to be a problem once the implementation period begins. Manufacturers of the device say they are committed to meeting market demand for 2008. In fact, manufacturers have been producing combination AFCIs since they were first required in the 2005 NEC. And although the same arguments were made at the time of the introduction of the branch/feeder AFCI into the NEC, all of the AFCI manufacturers delivered product to meet market demand.

Historically, there are numerous examples of Code requirements where a product may not have been available from every manufacturer at the time of Code development. Those manufacturers, however, completed development and manufacturing in time to meet implementation dates. Examples include past requirements for the 240V ground fault circuit interrupter (GFCI), potting compounds for wet niche fixtures, and in-use receptacle covers.

The bottom line

Some have argued that there should be a statistic indicating how many times AFCIs have prevented a fire from occurring, which currently is not a feasible request. The AFCI disconnects the power when an arc fault occurs; therefore, no incidence of fire or arc is reported to authorities. The same can be true when a smoke alarm siren alerts the homeowner, and the small smoking event is extinguished without incident. This statistic is not reported to the federal government or the local fire department. The only statistics reported are those that have resulted in a fire or response by a fire department. As such, many safety protection actions go unreported.

While functioning smoke alarms, fire extinguishers, and emergency safety ladders increase a family's chances of escaping injury from an electrical fire, AFCIs can prevent fires from occurring in the first place. This is why the 2008 edition of the NEC and previous editions of the NEC require AFCIs to be installed in homes.

Winstanley is a technical program manager with the National Electrical Manufacturers Association's (NEMA's) Low-Voltage Distribution Equipment section in Rosslyn, Va.

Sidebar: United Front

The expanded AFCI requirements have the support of the National Association of State Fire Marshals, the National Electrical Contractors Association (NECA), the Electrical Safety Foundation International, and the National Electrical Manufacturers Association (NEMA), among others.

The U.S. Consumer Product Safety Commission (CPSC) estimates that AFCIs could prevent more than 50% of electrical fires, and the U.S. Department of Housing and Urban Development (HUD) lists the technology as a key device in preventing burns and fire-related injuries.

Sidebar: The Evolution to Develop Arc Fault Technology

Research in the arc fault arena began in the late 1980s and early 1990s, when the Consumer Product Safety Commission (CPSC) identified a concern with residential fires of electrical origin. The CPSC discovered that one-third of electrical fires originated in the branch-circuit wiring systems of homes, which led to the first Code proposals to require AFCI protection.

The first requirement for AFCIs appeared in the 1999 NEC under Sec. 210.12. Subsequent NEC editions have further upgraded the requirements for its use. The 1999 edition rules, which became effective in 2002, required that dwelling unit bedrooms in new homes have AFCIs installed to protect only branch circuits that supply 125V, single-phase, 15A and 20A receptacle outlets.

After further research and analysis of the technology and its potential safety benefits, the 2002 edition updated Sec. 210.12 and expanded the requirement for AFCIs to include all bedroom circuits in new homes, including those that supply lighting fixtures, smoke alarms, and other equipment. Section 210.12 was again revised in 2005 to provide for a technology upgrade to the combination type of AFCIs. While previous generations of AFCIs detected parallel arcing, the combination AFCI could also detect series arcing.

The 2008 NEC further recognized the combination AFCI. In its attempt to take electrical safety a step further, it now requires that all new home construction install combination AFCIs in additional living areas in the home as well as bedrooms.

About the Author

Gerard Winstanley

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