The Truth About AFCIs
Part II
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IAEI NEWS
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THE TRUTH ABOUT AFCIs
by George Gregory and Alan Manche
T
his is the second of a two-part article on arc-fault
circuit interrupters (AFCIs). The first part was
published in the January/February issue of this
magazine and dealt with questions related to the technology and how it is addressed in the product standard. Part II focuses on application and installation in
accordance with the National Electrical Code. AFCIs
have just become required for installation in residences
under the NEC. The intent of this article is to enlighten
the reader on facts about AFCIs.
Background
branch circuits that supply receptacle outlets in bedrooms. One revision confirmed that the AFCI must protect the “entire” branch circuit. Another replaced the
term “receptacle outlets” with simply “outlets” and required that all outlets—including those for lights, fans
and smoke alarms—be protected as well as receptacle
outlets. These changes affirm that NEC Code-making
Panel 2 (CMP-2) intends that fixed wiring be protected
and that all wiring associated with bedrooms be covered by the rule.
As regards what must be protected, the requirement
is clear as written: “All branch circuits that supply 125volt, single-phase, 15- and 20-ampere outlets installed
in dwelling unit bedrooms shall be protected by an
arc-fault circuit interrupter listed to provide protection
of the entire branch circuit.”1 This includes outlets for
receptacles, for lights, for
fans, and so forth in circuits
that supply bedrooms.
AFCIs are not new, but they are newly applied under
the NEC rules. A variety of questions have arisen regarding where they must
be applied, whether to expect unwanted operation,
and how to test and service
installations. This part of
the two-part article anRetrofit applications in
swers some of those ques2-wire circuits
tions.
A branch/feeder AFCI (circuit
Electricians, contractors
breaker type) provides good
and users should be aware
protection for 2-wire cirthat AFCIs are installed in locuits. It provides for deteccations that the standard cirtion of a low-level short circuit breakers are installed.
cuit of 75 amperes or above
They can be retrofitted
that would not be detected
into existing loadcenters
by an overcurrent protective
and panelboards. Electrical
device. It also provides deconnections are similar to
tection of an arcing ground
those of a circuit breaker
fault occurrence of 5 amBranch/circuit-breaker
GFCI in that they have a
peres or above. Note that
type AFCI
load-neutral connector and
commercially available
a pigtail connection to the
AFCIs actually detect arcing
panel neutral bus.
ground fault of 50 milliamIt should be very difficult to cause an unwanted trip- peres and above even though 5 amperes is the stanping condition in a dwelling unit branch circuit. When dard requirement. This protection is as valid in 2-wire
tripping occurs, it is most likely a result of an arcing circuits as in 3-wire circuits that include the grounding
condition or an improperly wired circuit. The AFCI is conductor. The difference is that with the added
designed to trip when certain conditions likely to cause grounding conductor in the 3-wire circuit, an arc of
a fire exist in the circuit. There has been relatively little any level may reach the grounding conductor and be
experience in locating these conditions. This paper pro- detected at levels below 75 amperes, which provides a
vides some guidelines that may be helpful. Part I of the degree of protection not available in 2-wire circuits.
article lists conditions under which the AFCI is designed
to trip. The discussion focuses on the branch/feeder AFCI, Required locations under the NEC
Article 100 of the NEC defines a dwelling unit as: “One
which is the only commercially available AFCI.
or more rooms for the use of one or more persons as a
housekeeping unit with space for eating, living, and
Applying AFCIs under NEC 210.12
As mentioned in Part I of this article, the NEC 2002 sleeping, and permanent provisions for cooking and
retained, with only minor revisions, the requirement sanitation.” AFCIs are required in specified circuits that
of the NEC 1999 that AFCI protection be required on supply dwelling unit bedrooms. The following points
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MARCH/APRIL 2003
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THE TRUTH ABOUT AFCIs
are from questions that have arisen regarding circuits
to be protected.
Hotels and dormitories
One question that has arisen is whether hotel or motel
rooms and dormitories are considered dwelling units.
The rule must be interpreted by the authority having
jurisdiction (AHJ). If the AHJ considers these units
dwelling units, they must be so considered for NEC
210.12. One way to make this judgment is to consider
whether the units would constitute a dwelling unit if
the facility were placed under new ownership and occupied as apartments or condominiums.
Smoke detector circuits
Circuits supplying smoke detectors in bedrooms fall
under the category of bedroom outlets. Recall that the
purpose of the AFCI is to address fire causes. If the
potential fire cause is in the smoke detector wiring,
the first approach for protection against fire should be
to clear the potential cause. Further, listed smoke detectors are required to have battery back up, so that
power to the smoke detector is not dependent on the
presence of power from the utility.
Bedroom closets
Whether bedroom closets are part of the bedroom is a
judgment to be made by the AHJ. However, it is clear
that the intent of 210.12 is to provide protection for
the entire bedroom. When the closet is an integral part
of the bedroom, a safe approach would call for the
closet wiring to be protected just as other parts of the
bedroom.
Commercial applications
Although not required under the NEC, AFCIs are suitable for use in commercial applications in circuits for
which they are rated.
Tripping causes on installation
Causes of tripping of branch/feeder AFCIs are listed
in Part I of this article. Understandably, it is frustrating to install a device and find that it trips as soon as
it is turned on. It is important to understand that
where single-pole AFCIs are used, the neutrals of two
or more circuits cannot be shared, mixed or crossed.
Also, if the neutral is grounded on the load side of
the AFCI, the AFCI may trip.
Because there were a significant number of reports
of AFCIs tripping on installation, Square D re-contacted those who had reported the tripping after the
initial inquiry from them. The following is a list of
the findings.
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IAEI NEWS
AFCI ADOPTION
In the interest of providing up-to-date information regarding AFCIs, we have provided this
tabulation of states and localities that have
adopted the requirements of NEC 210.12. The
information is the latest the authors have found
from public sources. It is constantly changing.
2002 NEC Adoption
The following states have adopted the 2002
NEC and are enforcing an AFCI requirement in
210.12 as indicated:
State
NEC 210.12 Enforced
AK
Yes
AR
Yes
CO
Yes
GA
Yes
ID
Yes
IN
Yes
KY
Yes
MA
Yes
ME
Yes
MN
Yes
MT
Yes
NC
Yes
ND
Yes
NE
No
NH
Yes
OH
Yes
OR
Yes
RI
Yes
SC
Yes
SD
Yes
UT
Yes
WA
Yes
WY
Yes
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1999 NEC Adoption
The following states have adopted the 1999
or earlier edition of the NEC and are enforcing
an AFCI requirement in 210.12 as indicated:
State
NEC 210.12 Enforced
CT
No
DE
Yes
FL
Yes
IL
Yes
MI
No
NJ
No
NM
Yes
OK
Yes
TX Yes - 1&2 family dwellings
VT
Yes
WI
No
CA
Yes
IA
1996 NEC
VA
1993 / 96 NEC
WV
1996 NEC
• 4 cases were unresolved.
• 1 was an application problem in which equipment
of two manufacturers was mixed on the job. The AFCI
worked fine and continues to do so.
• 6 were resolved by reading the instructions. The
callers had not initially understood how the AFCI was
to be used.
• 1 was a bad appliance, a room air conditioner.
• 23 were wiring problems broken down as follows.
1 problem at a connector in which wires were
too close
4 crossed neutrals
7 shared neutrals
9 grounded neutrals
2 shared neutrals also grounded
Crossed neutrals are defined here as neutrals from
multiple circuits either crossed or touching. Shared
neutrals are defined here as multi-circuit neutrals.
Reported difficulties in troubleshooting installation
problems are an indication of a learning curve and are
not a reflection on poor performance of the AFCI.
Today’s AFCIs are performing their detection function
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Local Adoption States
The following states adopt the NEC by locality rather than by state. Cities that have adopted
the NEC with an AFCI requirement with either
the 2002 or 1999 edition are indicated. Where
only “local adoption” is indicated, details of
adoption are not available.
State
NEC 210.12 Enforced
AZ
Local Adoption
AL
Local Adoption
HI
Honolulu
KS
Local Adoption
LA
New Orleans
MD
Baltimore
MO
Local Adoption
MS
Local adoption
NV
Las Vegas, Reno
NY
Local Adoption
PA
Philadelphia
TN
Nashville, Knoxville
TX
Local Adoption for
other than 1&2 family dwellings.
properly and are finding problems that should be corrected. There is some resistance to this change as is
to be expected with any change. However, this small
and informal survey indicates that installers are learning the issues that are uncovered by AFCIs and that
they can be found and corrected. When the circuit is
corrected, not only is the circuit correct, it also has
additional AFCI protection operating to help retain it
free of hazardous arcing.
Shared neutrals
Single-pole AFCIs cannot protect circuits in which
the neutral (grounded circuit) conductor is shared or
mixed. The reason is that current flowing out and returning is monitored for the presence of arcing faults.
When single-pole AFCIs are applied, the circuit must
have a distinct hot and a distinct neutral conductor.
Otherwise, the AFCI cannot distinguish arcing groundfault occurrences.
Contractors and users should understand that there
are some drawbacks to using shared neutrals. For example, if a 2-pole, common-trip version is used, then
both circuits are interrupted during a fault. If the 2-pole,
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THE TRUTH ABOUT AFCIs
common-trip version is used, then both circuits are interrupted during a fault. If the 2-pole circuit breaker has
independent trip, then when a circuit is tripped and an
outlet device is removed (assuming a dead circuit), if
the home run is split at that point, the wiring in the box
is not really dead. Another example of shared neutral
wiring disadvantages is the result if the home run neutral is lost—a motor load will take one side of the circuit
to zero, putting the loads on the other side to 240 volts.
This tends to play havoc with many 120-volt devices.
Further, cable manufacturers are apparently planning
cables that contain four wires plus ground for exactly
this kind of application.
Test equipment
Availability of test equipment has been questioned for
three purposes:
a. To verify that the circuit has been installed properly so that contractors can demonstrate that their work
has been done competently.
b. To verify that the AFCI is functioning properly.
c. To trip an AFCI from a load circuit in order to
identify which AFCI is in the circuit.
We will discuss each item briefly.
Verification of the installation
The authors are not aware of special equipment available to test the circuit for proper installation beyond
that which has been available without the AFCI. If wiring is installed competently, there should be no reason
for any testing that is not done for a circuit without an
AFCI. However, there are two possible practices that
can be used to test the installation, if a test is desired.
1) Probably the best test is to install an AFCI, at least
temporarily in the circuit. For this test to be effective,
the circuit must be complete, since it must be energized as in service with 120 volts. Use the test button
to verify that the AFCI is functioning properly. Then
leave the AFCI in the energized circuit for some period
of time. If it does not trip, that is an indication that the
circuit is acceptable.
2) As with any installation, an insulation resistance
(Megger device) test can be done to verify that the wiring and connections are properly insulated. With this
test, high voltages are applied. Be sure to keep personnel away from circuits being tested and follow safety
practices described in NFPA 70E, Part II.
To perform this test, disconnect all loads and verify
that unconnected wire ends are insulated. Disconnect
the load wire to any AFCI or GFCI in the circuit because these devices may be damaged by high voltage.
Use an insulation resistance tester that will apply a direct current voltage of at least 500 volts to the circuit
under test. All resistance readings should be at least
one megohm (1,000,000 ohms). A successful test will
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IAEI NEWS
indicate that the insulation is intact and initiation of an
arc would be highly unlikely for the portion of the circuit tested.
Recognize that neither of these tests will identify
loose connections. Good workmanship is required as
always.
Verification of the AFCI
The most effective test is the self-test supplied with the
AFCI. See the instructions supplied with the AFCI by
the manufacturer. In accordance with UL 1699, this test
“simulates an arc such that the arc detection circuit or
software is caused to detect the simulated arc.” By
doing so, it tests all of the AFCIs systems and tripping
parts. An external tester is not necessary.
The authors are not aware of commercially available
testers other than those mentioned below that trip the
AFCI by applying a ground fault.
Tripping the AFCI from a load
There are several devices being marketed that will trip
the AFCI by applying a ground fault on the system. Be
aware that devices that are not listed for this purpose
may be creating a potential shock hazard by creating a
ground fault of sufficient current to trip the AFCI.
Finding the cause of AFCI tripping
One of the most frequently asked questions is about
how to find the cause of tripping when an AFCI trips.
There is no single correct answer to this question. An
orderly search is probably the best approach. We are
not aware of specialized equipment that would help
locate a problem. The skill and experience of the electrician will help. Remember that the circuit breaker AFCI
will trip from an overcurrent sensed by the circuit
breaker or from an arcing occurrence sensed by the
AFCI function, including a ground fault.
picture
Photo 2. A broken or separated conductor could cause a series arc.
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THE TRUTH ABOUT AFCIs
The AFCI function will be sensing an arc that occurs
because insulation or isolation is not adequate. The
problem or fault may be in one or a combination of
these three conditions:
1) Line-to-ground
2) Line-to-neutral
3) Series arc in broken or separated conductor (could
be a loose connection). Note that the branch/feeder
AFCI will not generally detect a series arc because series current is usually below the detection level.
Here are some steps that may be useful:
a) Gather information from people who have used the
circuit regarding any buzzing noises, visible arcing, the
odor of smoke, or similar indications of improperly
operating or defective appliances or equipment. This
information may lead to the fault location. If arcing is
suspected in an extension cord or a cord-connected
appliance, immediately unplug the suspected unit.
b) The most likely cause of tripping in a new installation is wiring. Check for neutral (grounded circuit)
conductors that are shared or crossed with those of
other circuits, or neutral conductors that are grounded
on the load side of the AFCI.
c) Unplug all appliance and extension cords connected
in the circuit. If tripping continues to occur when the
AFCI is turned on, the fault is in the fixed wiring system.
d) Similarly, turn off all fixed appliances such as lights
and ceiling fans that have switches. Since these circuits
cannot be fully disconnected (line, neutral and ground),
tripping occurrences with their switches turned off does
not necessarily mean that they are fault free.
e) If the AFCI does not trip when all plugs are disconnected, turn on the AFCI again and reconnect the
plugs one by one. Then turn on fixed lights and appliances. This procedure may locate the faulted cord or
appliance.
f) Because arcs are sometimes sporadic, turning off
the circuit may temporarily clear the arc and it may not
immediately reappear when the circuit is re-energized.
For this reason, the arc may not be located by unplugging and reconnecting appliances. If the arc has been
located to be in the fixed wiring system, or if the arc
has not been located by removing plug-in loads, some
of the following techniques may be helpful.
• Examine appliance cords, plugs and equipment
carefully for indications of damage.
• With the circuit de-energized, examine connections
to the AFCI, receptacles, lighting fixtures and other
appliances.
Note: De-energize the load center by turning off the
main disconnect, if possible, before conducting the
following checks. By means of a reliable voltmeter,
verify that voltage is not present.
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g) Apply the insulation resistance test described in a
response to a question above to check for insulation
adequacy line-to-neutral, line-to-ground and neutralto-ground. Alternatively, use an ohmmeter to check for
electrical continuity line-to-neutral, line-to-ground and
neutral-to-ground. Continuity indicates presence of a
fault. The insulation resistance check is the preferred
method.
h) Indication of adequate insulation in a circuit that
has been identified as having an arc fault may point to
a series fault, that is a broken conductor or a loose
connection.
i) The line-to-ground sensing is for small leakage
current of about 50 milliamperes (0.050 amperes) and
above. It may not be visible as an arc. Any technique
used to find a ground fault would be useful for locating an arc to ground.
j) Once the fault is located, damage must be repaired
or improperly operating equipment or appliances must
be replaced.
k) In most cases, the steps noted above will help
locate the fault. It is important to recognize that the
AFCI has provided an indication of a condition that
could become a fire hazard. Do not continue to use
the circuit without a correction.
The introduction of AFCIs is a change. There is a
learning curve for the entire industry. Through this
change, it is clear that AFCIs are finding problems with
installations, both in older upgrades and in new construction, in fixed wiring as well as in extensions to
loads. The data indicates that there are many potential
fire causes that the AFCI will help avoid becoming fires.
When they are applied as intended, we will see results
in more potential fire causes corrected.
1
Section 210.12(B), National Electrical Code 2002, (National Fire
Protection Association, Quincy, MA), p. 70-54.
George Gregory is manager of Industry Standards, Schneider Electric/
Square D Company, Cedar Rapids,
Iowa. He is a registered P. E. in Iowa,
Illinois, and Puerto Rico. He serves on
NEC Panel 10 representing NEMA, and
has been an associate member of IAEI
since 1972.
Alan Manche is manager of Industry Standards, Codes and Inspector
Relations, Schneider Electric/Square
D Company, Lexington, KY. He is a
registered P.E. in Kentucky. He serves
on a number of NFPA Technical Committees including NEC Panel 8, NFPA
70B and NFPA 73. He is an active participant in NEMA, UL, CSA, NFPA and
IAEI.
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