Arc Fault Circuit Interrupters

Arc Fault Circuit Interrupters
arc fault circuit interrupters
advanced
technology
using
to reduce
electrical fires
NATIONAL ELECTRICAL MANUFACTURERS ASSOCIATION
Low Voltage Distribution Equipment Section
I N T R O D U CT I O N
Arc Fault Circuit Interrupters (AFCIs) are required by
the National Electrical Code for certain electrical
circuits in the home. Questions have been raised
regarding their application and even the need for
them. Various technical “opinions”, organizational
“marketing pitches”, and misinformation is being
distributed about AFCIs that further mislead the public
about the purpose of the device as a part of overall
electrical safety for the public.
damage or destroy significant amounts of property.
Electrical fires can be a silent killer occurring in areas
of the home that are hidden from view and early
detection. The objective is to protect the circuit in a
manner that will reduce its chances of being a source
of an electrical fire.
T H E J O U R N EY TO D E V E LO P D ET E CT I O N
T E C H N O LO GY
Research in the arc fault area began in the late 1980’s
and early 1990’s when the Consumer Product Safety
Commission (CPSC) identified a concern with the
residential fires of electrical origin. A large number of
these fires were estimated to be in branch circuit
wiring systems.
The concept of AFCIs gained more momentum
when code proposals were made to the 1993 NEC®
to change the instantaneous trip levels of 15A and
20A circuit breakers. The Electronic Industries
Association (EIA) had studied the issue of electrical
fires and determined that additional protection against
arcing faults were an area that needed to be
addressed by electrical protection. This proposal first
attempted to do this by requiring that instantaneous
trip levels of a circuit breaker be reduced from a range
of 120 to 150 amperes down to 85 amperes.
However, it became clear that the lowering of those
levels below some of the minimums already available
on the market would result in significant unwanted
tripping due to normal inrush currents.
This brochure is intended to address the various aspects
of AFCIs and clear up the misinformation circulating in
the industry.
W H Y D O W E R E A L LY N E E D A F C I s ?
Smoke alarms, fire extinguishers and escape ladders
are all examples of emergency equipment used in
homes to take action when a fire occurs. An AFCI is
a product that is designed to detect a wide range of
arcing electrical faults to help reduce the electrical
system from being an ignition source of a fire.
Conventional overcurrent protective devices do not
detect low level hazardous arcing currents that have
the potential to initiate electrical fires. It is well known
that electrical fires do exist and take many lives and
It was these early studies and code efforts that led to the
first proposals requiring AFCIs, which were made during
the development of the 1999 NEC. NEC Code-Making
Panel 2 (CMP2) reviewed many proposals ranging from
protecting the entire residence to the protection of living
and sleeping areas. In addition, the panel heard
numerous presentations on both sides of the issue. After
much data analysis and discussion, the CMP2 concluded
that AFCI protection should be required for branch
circuits that supply receptacle outlets
in bedrooms.
Subsequent editions of the NEC
further upgraded the requirements
to include protection on all outlets
(lighting, receptacle, smoke alarm,
etc.) in bedrooms along with other
enhancements.
© 2004 NFPA
Furniture pushed against or
resting on electrical cords can
damage the wire insulation.
Damaged cords can become a
potential condition for arcing.
Extension or appliance cords
that are damaged or have
worn or cracked insulation can
contribute to electrical arcing.
Parallel Arc
Series Arc
Cord insulation can be
deteriorated by heat generated
by hot air ducts or sunlight.
W H AT A R E A R C FA U LTS ?
The UL Standard for AFCIs (UL 1699) defines an arcing
fault as an unintentional arcing condition in a circuit.
Arcing creates high intensity heating at the point of
the arc resulting in burning particles that may over
time ignite surrounding material, such as wood
framing or insulation.
The temperatures of these arcs can exceed 10,000
degrees Fahrenheit. Repeated arcing can create carbon
paths that are the foundation for continued arcing,
generating even higher temperatures.
typical causes
Cables that are improperly
nailed or stapled too tightly
against a wall stud can sever
insulation and cause arcing.
Wires located behind walls can
be accidentally punctured by a
screw or drill bit damaging the
insulation of the wiring.
Nails carelessly driven into
walls can break wire insulation
and cause arcing.
of arc faults
Example conditions where arc faults may start include:
• Damaged wires
• Worn electrical insulation
• Wires or cords in contact with vibrating metal
• Overheated or stressed electrical cords and wires
• Misapplied or damaged electrical appliances
Cords caught in door jams can
deteriorate the cable insulation
through the action of opening and
closing, allowing arcing to occur.
F I R E DATA A N A LYS I S
The National Fire Protection Association, the insurance
industry and others track the incidence of electrical
fires across the United States and categorize those
fires based on their causes. In reviewing statistics
dating back to 1999, fires in the home electrical
system exceed 31,000 annually.*
Updated figures from a March 2006 report of the
U.S. Department of Housing and Urban Development
(HUD) – (“Healthy Home Issues: Injury Hazards”) –
provides additional support for the need to protect
residences and their occupants:
“Electrical problems spark an estimated 67,800 home
fires on an annual basis, according to the most recent
data from the United States Fire Administration
(USFA). The USFA is an agency of the federal
government and is committed to reducing the number
of deaths and economic losses due to fire and related
emergencies. The USFA also reports that electrical fires
kill 485 innocent victims and injure approximately
2,300 others, while causing $868 million in residential
property damage each year.” (USFA. 2006. On the
Safety Circuit: A Factsheet on Home Electrical Fire
Prevention. U.S. Fire Administration)
The HUD recommendation was to promote AFCIs as
one of the many devices that can be used to prevent
burns and fire related injuries. In addition, it cites a
1999 CPSC Report recommending the use of AFCIs to
“prohibit or reduce potential electrical fires from
happening”.**
As you can see from the data above, fires of electrical
origin are a significant issue that must be addressed.
Frequently, it is argued that fires only occur in older
homes. However, it should be recognized that new
homes become older homes. It is critical to install the
AFCIs in the beginning so that they can perform their
protection function from the start. Seldom are devices
such as AFCIs added to homes after they are
constructed and occupied.
*Ref: 1999 Revised - 2002 Residential Fire Loss Estimates, U.S. National
Estimates of Fires, Deaths, Injuries, and Property Losses from
Unintentional Fires, U.S. Consumer Product Safety Commission, November
2005
**Healthy Homes Issues: Injury Hazards, U.S. Department of Housing and
Urban Development, Version 3, March 2006
H O W I S A N A R C FA U LT D ET E CT E D ?
Unlike a standard circuit breaker detecting
overloads and short circuits, an AFCI utilizes
advanced electronic technology to “sense” the
different arcing conditions. While there are different
technologies employed to measure arcs by the
various AFCI manufacturers, the end result is the
same, detecting parallel arcs (line to line, line to
neutral and line to ground) and/or series arcs
(arcing in series with one of the conductors).
How does arc fault detection work? In essence,
the detection is accomplished by the use of advanced
electronic technology to monitor the circuit for the
presence of “normal” and “dangerous” arcing
conditions. Some equipment in the home, such as
a motor driven vacuum cleaner or furnace motor,
naturally create arcs. This is considered to be a normal
arcing condition. Another normal arcing condition that
can sometimes be seen is when a light switch is
turned off and the opening of the contacts creates
an arc.
A dangerous arc, as mentioned earlier, occurs for
many reasons including damage of the electrical
conductor insulation. When arcing occurs, the AFCI
analyzes the
characteristics of the
event and determines if it
is a hazardous event.
AFCI manufacturers test
for the hundreds of
possible operating
conditions and then
program their devices to
monitor constantly for
the normal and
dangerous arcing
conditions.
T H E N E C ® A N D U L ® STA N DA R D
National Electrical Code®
The National Electrical Code® specifically
defines and mandates the installation of
AFCIs. In the 1999 edition of the NEC, Section
210.12 required that dwelling unit bedrooms have AFCIs
installed to protect all branch circuits that supply 125volt, single-phase, 15 and 20-ampere receptacle outlets
installed in the dwelling unit bedrooms. This
requirement became effective January 1, 2002.
In the 2002 edition, the update of section 210.12
expanded AFCI protection to all bedroom outlets
(lighting, receptacle, smoke alarm, etc.).
The 2005 NEC 210.12 revised the AFCI requirement to
provide for a technology upgrade. While previous
generations of product detected parallel arcing, this
new device – a combination AFCI – would also detect
series arcing, and at lower current levels.
UL Standard
Product standards to cover AFCIs began
to be developed in the mid 1990’s.
Underwriters Laboratories published UL
1699 – Standard for Safety for AFCIs - in 1996 to cover
a wide variety of conditions to evaluate an AFCI. The
standard includes requirements for the following
conditions:
• Humidity Conditioning • Leakage Current
• Voltage Surge
• Environmental Evaluation
• Dielectric Voltage
• Arc-Fault Detection
• Unwanted Tripping
• Operation Inhibition
• Resistance to Environmental Noise
• Abnormal Operation
One of the most frequent questions about AFCIs is
related to resistance to unwanted tripping. There are
four varieties of tests related to its ability to resist
unwanted tripping.
• Inrush Current: High current draw devices such as
tungsten filament lamps and capacitor start motors.
• Normal Arcing: Brush motors, thermostatic contacts,
wall switch and appliance plugs.
• Non-Sinusoidal Waveforms: Examples of devices
creating these electrical waveforms include
electronic lamp dimmers, computer switching-mode
power supplies and fluorescent lamps.
• Cross Talk: This test measures trip avoidance for an
AFCI when an arc is detected in an adjacent circuit.
Only the circuit with the arc should cause the
breaker to trip, not another circuit.
Through the use of the National Electrical Code
requirement and extensive UL testing, manufacturers’
AFCI products provide superior protection against
arcing faults.
C O N T R A ST I N G A F C I A N D G F C I
There is a major difference between the functioning of
an AFCI as compared to a GFCI (Ground Fault Circuit
Interrupter). The function of the GFCI is to protect people
from the deadly effects of electric shock that could occur
if parts of an electrical appliance or tool become
energized due to a ground fault. The function of the AFCI
is to protect the branch circuit wiring from dangerous
arcing faults that could initiate an electrical fire.
AFCI and GFCI technologies can co-exist with each
other and are a great complement for the most
complete protection that can be provided on a circuit.
W H AT A R E T H E VA R I O U S S A F ET Y A N D
G O V E R N M E N TA L A G E N C I E S S AY I N G
ABOUT AFCI?
“The National Association of State Fire Marshals
(NASFM) strongly supports the broad adoption of AFCI
technology through national, state, and local building
codes. AFCIs are the most welcome addition to fire
prevention in decades. AFCIs promise to save
hundreds of lives every year.”
John C. Bean, President, NASFM
“The National Association of Home Inspectors (NAHI)
strongly encourages its members to educate all of
their clients about the life and property saving
benefits of AFCI technology, especially those clients
considering the purchase of a home more than 20
years old.”
Mallory Anderson, Executive Director
“The National Electrical Contractors Association
(NECA) submitted comments to legislative committees
in Michigan and South Carolina, urging them to retain
requirements for AFCI protection of bedroom
receptacles in their state electrical codes. Cost cutting
pressure from homebuilders’ association in both
states led to code proposals to delete AFCI protection
required by the National Electrical Code, when
constructing new homes.”
NECA Contractor Code Letter
“CPSC has identified arc fault circuit interrupter (AFCI)
technology as an effective means of preventing fires
caused by electrical wiring faults in homes.”
U.S. Fire Administration
“The Electrical Safety Foundation International (ESFI)
urges that arc fault circuit interrupter (AFCI)
technology be installed in all new and existing
housing to protect homes and families from fires
caused by electrical arcing.”
Brett Brenner, President, ESFI
T Y P E S O F A F C I A R C FA U LT C I R C U I T
I NTERRU PTER (AFCI)
AFCIs are intended to mitigate the effects of arcing
faults by functioning to de-energize the circuit when
an arc fault is detected. AFCIs are required by the
NEC® to be a listed product. This means that they
must be evaluated by a nationally recognized testing
laboratory to the national standard for AFCIs (UL
1699). NEC 210.12 establishes the requirement to use
AFCIs. Protection is required for branch circuits in
locations as specified in this NEC® rule.
Branch/Feeder AFCI
A device intended to be installed at the origin of a
branch circuit or feeder, such as at a panelboard. The
branch/feeder AFCI provides for detection of arcing
faults that can occur line-to-line, line-to-neutral and
line-to-ground.
To be able to handle shared neutral circuits (a
common application in older homes), a two-pole AFCI
can be used. This will accommodate the three-wire
circuit arrangement used in shared neutral
applications.
Combination AFCI
In addition to the protection provided by the Branch
Feeder AFCI, the Combination AFCI provides for series
arc detection down to 5 amperes. This series arc
detection is
beneficial to detect
lower level arcing
in both branch
circuits and power
supply cords.
Combination
AFCI protection
is required by the
NEC as of
January 1, 2008*.
AFCI and GFCI Protection
An AFCI can be used in conjunction with GFCI
protection to provide both arcing fault protection as
well as 5mA ground fault (people) protection. A
common way to provide both types of protection is to
use an AFCI circuit breaker and a GFCI receptacle.
AFCIs can also incorporate 5mA GFCI protection into
the same package. This solution for AFCI and GFCI on
the same circuit can be useful where the circuit design
requires both types of protection or where the installer
(or user) wants to have both types of protection.
* The 2005 NEC® added the requirement for combination AFCI protection,
but implemented an effective date of January 1, 2008.
W I R I N G A N D I N STA L L AT I O N G U I D E L I N E S
There are no special requirements of an AFCI circuit
other than proper installation and wiring practices. There
are various special considerations that must be given to
certain circuits that vary from the norm, such as shared
neutral applications, but in general the application of an
AFCI is as simple as following the installation instructions
that come from the manufacturer.
The basic difference between installing the AFCI versus
a standard thermal magnetic circuit breaker is the
requirement to connect both the hot and neutral
conductor to the proper terminals of the AFCI. In a
circuit wired with
a conventional
circuit breaker, the
hot conductor is
connected to the
breaker and the
neutral conductor
is connected
directly to the
neutral bar of the
load center.
defining the
arc fault risk
to people and property
As with any change in the required protection for the
electrical system, there have been many discussions
and deliberations both for and against arc fault
protection being a part of the National Electrical Code.
Some have argued that the cost of the AFCI is higher
than a standard circuit breaker and, as such, it costs
too much to provide the increased protection. Others
have argued that since it is a relatively new type of
protection, it does not have the history on which to
base a decision as to whether to support or not.
These comments have been debated thoroughly and
completely. It is important to keep a few critical facts
in mind.
• According to Electrical Wholesaling Magazine (Sept.
2006), on an average size home of 2,500 square feet
the average total cost is $192,846. As per the
Consumer Product Safety Commission,* the average
professionally installed cost differential between an
AFCI and a standard circuit breaker is between $15
and $20. With the average number of circuits
requiring AFCIs being 12, this equates to an
approximate cost increase of $180 to the homeowner,
or .093% of the national average home cost.
• The Consumer Product Safety Commission staff
report on Estimated Residential Structure Fires on
Selected Electrical Equipment (October 2006) from
1999-2003 reported that 142,300 electrical
distribution fires occurred on all distribution
components. Installed wiring fires were estimated to
have occurred in 50,200 instances. Taking these
CPSC statistics into account, one has to ask that if a
portion of the 50,200 fires could have been
prevented, would the $180 have been worth the
increased cost to the homeowner?
Using the same report, the CPSC projected that there
were 910 deaths attributed to electrical distribution
equipment during that five-year period. Installed wiring
led to approximately 210 deaths as a part of that total.
Applying technology to improve the electrical safety of
the home is a wise investment for both the homeowner
and the community at large. Reducing fires of electrical
origin and saving lives is an important responsibility of
the entire construction and regulatory community.
* CPSC Memorandum of March 10, 2003 titled: “Economic Considerations
– AFCI Replacements” stated that “the average cost differential between
AFCI Circuit Breakers compared to Residential Circuit Breakers without the
AFCI feature is $15 - $20 per unit.”
what is the price of new
safety technology worth?
When Ground Fault Circuit Interrupters (GFCIs) were
introduced in the 1970s, similar discussions took place
regarding the cost/benefit to the consumer,
homebuilder and others. GFCIs have been a standard
requirement in homes for over 30 years with
additional locations and circuits being added over time
as well. GFCI also has a statistical track record over
time as to the reduction of electrocutions. On an
annualized basis, in 1983, there were almost 900
electrocutions total per year with approximately 400
being consumer product related. Ten years later, the
total was reduced to 650 annually and slightly over
200 consumer product electrocutions annually.
established by a national body of experts that have
heard testimony from many sources as well as
reviewed a significant amount of data to make their
recommendation. Shouldn’t we trust the safety experts
that develop our safety procedures?
To learn more about the safety benefits of AFCIs,
please visit our AFCI web site at www.afcisafety.org.
With over 20 years of history, statistically based
analysis of GFCIs was built on a solid foundation of
data. AFCIs are new and have only been installed in
new construction on bedroom circuits for a few years.
As with all products, given time, they too will be able
to provide a solid statistical base of measure.
Some have argued that it should be shown how many
times an AFCI has ”prevented“ a fire from occurring. Of
course, this 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. Is that statistic reported to the Federal
Government or local fire department? Of course not.
Safety prevention is just that ... prevention. The only
statistics that are reported are those that have resulted in
a fire or a response of a fire department. Many safety
protection actions go unreported.
If we are to offer consumers a safer home, then the
appropriate technology should be put into place.
Removing AFCI as a local or state code requirement
is reducing safety requirements. These rules are
N E M A A N D E L E CT R I C A L S A F ET Y
For more than 80 years, manufacturers of Low Voltage
Distribution Equipment have been working to ensure
public safety through standards writing efforts and the
dissemination of important industry information
through the National Electrical Manufacturers
Association (NEMA), one of the most respected
standards development organizations in the world.
Headquartered in Rosslyn, Virginia, NEMA has
approximately 400 electroindustry companies,
including large, medium and small businesses. To
learn more about NEMA visit www.nema.org.
NATIONAL ELECTRICAL MANUFACTURERS ASSOCIATION
Low Voltage Distribution Equipment Section
1300 North 17th Street, Suite 1752 • Rosslyn, Virginia 22209
(703) 841-3200 Fax: (703) 841-5900
www.nema.org
National Electrical Code,®
NEC® and NEC logo are
registered trademarks of the
National Fire Protection
Association. UL logo is a
registered trademark of
Underwriters Laboratories, Inc.
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement