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Arc Fault Circuit
Interrupters (AFCIs)
Understanding the Problem of Arc Faults and House Fires
According to the Consumer Products Safety Commission (CPSC), approximately
40,000 fires are caused annually by problems with home electrical wiring.
For the last five years, electrical wiring systems have been one of the
leading causes of fire deaths, claiming between 260 and 380 lives per year
and costing more than $650 million annually.
In 1998, according to the latest statistics released by the CPSC,
fire originating in the electrical distribution system accounted for
more than 10 percent of all home fires.
What is an Arc Fault?
Many times the culprit is an arc fault. An arc is a discharge of electric
current across a gap. Many of us have seen an arc such as from an arc welder
or sparks from a downed power line. An arc fault is an unintended arc
flowing through an unintentional path.
Common causes for arc
faults in a house are:
-
Loose or improper
connections, such as electrical wires to outlets or switches
-
Frayed or ruptured
appliance or extension cords
-
Pinched or pierced
wire insulation, such as a wire inside a wall nipped by a nail or screw or
a chair leg setting on an extension cord
-
Cracked wire
insulation stemming from age, heat, corrosion or bending stress
-
Overheated wire or
cords
-
Damaged electrical
appliances
-
Wires or cords
touching vibrating metal
-
Electrical wire
insulation chewed by rodents
When an arc fault
occurs inside the walls or ceiling, or inside an electrical appliance,
temperatures can exceed 10,000° F. Nearby combustibles like wood studs or
insulation can be ignited by an electrical arc.
Fortunately, companies have developed arc fault circuit interrupters (AFCI)
to help avoid fires caused by arc faults. They look and work just like
conventional circuit breakers and fit into electrical panels in the same
way. But they provide additional protection against arc faults.
Conventional circuit breakers "trip" if an overload or short circuit is
detected, which shuts off the electrical power. They protect against
overloads and short circuits with thermal and magnetic protection,
respectively. AFCIs, however, not only protect against overloads and short
circuits, they can also electronically sense arcing and "trip."
Code Requirements
This breakthrough technology, first developed by electric utility companies
to deal with downed power lines, prompted the National Electrical Code (NEC)
to require that AFCIs be used on home bedroom circuits by 2002. In fact,
industry experts believe AFCIs will eventually be required on all home
circuits. The NEC elected to require them on bedroom circuits first because
a CPSC study showed many home fire deaths were related to bedroom circuits.
However, some code jurisdictions may choose not to adopt the section of the
NEC (Section 210.12) requiring the installation of AFCIs. Check with local
code officials if you have questions.
Costs
Initially, the cost for AFCIs was relatively high … between $75 and $160 as
compared to $10 to $20 for each conventional circuit breaker. The cost has
dropped to around $40 to $50 each.
Assessing Your Situation
Many in the construction industry may not be aware of the technology or its
use because AFCIs have only recently become code required. Electrical panel
manufacturers can assist in getting information about AFCIs.
It is difficult, if not impossible, to know whether your house has an arc
fault problem or the potential for one. One study has suggested that nearly
80 percent of all residential electrical fires occur in homes that are more
than 20 years old.2 AFCIs may be important to use in older houses that may
have aged or damaged electrical wire insulation. Newly constructed houses
also may have electrical wires nicked by nails and screws that are concealed
inside walls and ceilings.
An AFCI should not be confused with a Ground Fault Circuit Interrupter
(GFCI). They are completely different and serve two totally different
purposes. See the article on Ground Fault Circuit Interrupters for more
information.
How to Proceed
Installing AFCIs in your home requires a qualified electrician. The AFCIs
snap into the electrical panels similar to conventional circuit breakers. It
is typical that electrical panel manufacturers also make the circuit
breakers that fit into their panels. Circuit breakers are (generally) not
interchangeable in other manufacturers’ electrical panels. There is one
manufacturer that is developing a circuit breaker series, including AFCIs,
that can be installed in any manufacturer’s electrical panel.
And at this time, most electrical panel manufacturers make AFCI circuit
breakers. It is possible, however, that existing electrical panels in older
homes may have to be replaced if the panel manufacturer does not have an
AFCI available.
Currently, AFCIs are available in circuit breaker form only. Some electrical
product manufacturers are developing electrical outlets that will have AFCI
protection.
Sources of information about AFCIs can be obtained from the CPSC, the
National Fire Protection Association, Underwriters Laboratories (UL), your
local fire department, an experienced electrical contractor, or electrical
supply store. |
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