Download ARC FAULT CIRCUIT INTERRUPTER

ARC-FAULT CIRCUIT
INTERRUPTER(AFCI)
Presented by
Honey Baby George
S7,EEE
Roll no-21
CONTENTS
1.
Introduction
2.
Arc fault Circuit Interrupter
(AFCI)
3.
AFCI Working
4.
Types of AFCIs
5.
Arcing
6.
Where AFCI should be used
7.
Installing AFCI
8.
Testing AFCI
9.
Conclusion
10.
References
INTRODUCTION
 Annually, 40,000 fires - 300 deaths - over 1,400 injuries
 Arcing faults are the major cause of residential fires. In 1994 an
insurance company survey of 660 electrical fires indicated that over
33% of these fires were from arcing condition.
 An arc fault is the flow of electricity over an unintended path.

Unwanted arcing generates high temperatures and
discharges
molten
metal that can
ignite nearby
combustibles such as paper, insulation, vapors, and
carpets.

Temperature
-several
thousand
degrees
Celsius
depending on the available current, voltage, and
materials involved.
•A circuit breaker
protects electrical branch circuit wiring.
reduce the risk of fire from overheating.
•Circuit protection device’s role interrupts the current
before
the heat generated by an overload or fault damages the
wire's electrical insulation
the heat generated by an overload reaches temperatures
that could result in a risk of fire.
•At overload condition, the current drawn by the sum
of the electrical loads , connected to a particular
circuit, exceeds the current capacity (ampacity) of the
circuit conductors.
ARC FAULT CIRCUIT INTERRUPTER

Designed to prevent fires by detecting
a non-working electrical arc.

Disconnect the power before the arc
starts a fire.

It should distinguish between a
working arc and a non-working arc
that can occur.
Arc Faults Arise From A Number Of Situations, Including:
• Damaged Wires
• Receptacle Leakage
• Worn Electrical Insulation
• Loose Electrical Connections
• Shorted Wires
• Wires Or Cords In Contact With Vibrating Metal
• Overheated Or Stressed Electrical Cords And Wires
• Misapplied/Damaged Appliances
AFCI WORKING
*Conventional circuit breakers only respond to overloads
and short circuits, so they do not protect against arcing
conditions that produce erratic current flow.
*An AFCI is selective so that normal arcs do not cause it to
trip.
*It circuitry continuously monitors current flow through the
AFCI to discriminate between normal and unwanted arcing
conditions.
*Once an unwanted arcing condition
is detected, the control circuitry in the
AFCI trips the internal contacts, thus
de-energizing the circuit and reducing
the potential for a fire to occur.
*An AFCI should not trip during
normal arcing conditions, which can
occur when a switch is opened or a
plug is pulled from a receptacle.
•AFCIs have a test button and look similar to ground fault circuit
interrupter circuit breakers.
• Some designs combine GFCI and AFCI protection.
•AFCIs are designed to mitigate the effects of arcing faults but
cannot eliminate them completely.
• In some cases, the initial arc may cause ignition prior to
detection and circuit interruption by the AFCI.
•The AFCI circuit breaker serves a dual purpose –
shut off electricity in the event of an “arcing fault”
trip when a short circuit or an overload occurs.
•The AFCI circuit breaker provides protection for the branch circuit
wiring and limited protection for power cords and extension cords.
•Single-pole, 15- and 20- ampere AFCI circuit breakers are presently
available.
TYPES OF AFCIs
1. Branch/Feeder AFCI
2. Outlet Circuit AFCI
3. Combination AFCI
1. BRANCH/FEEDER AFCI
• Installed at the origin of a branch circuit or feeder, such as
at a panel board.
• Provide protection of the branch circuit wiring, feeder
wiring, or both, and branch circuit extension wiring. against
unwanted effects of arcing.
•It may be a circuit- breaker-type device or a device in its
own enclosure mounted at or near a panel board.
2. OUTLET CIRCUIT AFCI
• Installed at a branch circuit outlet, such as at an outlet
box.
• Provide protection of cord sets and power-supply
cords connected to it (when provided with receptacle
outlets)
3. COMBINATION AFCI
• Complies with the requirements for both branch/feeder and
outlet circuit AFCIs.
• Protect downstream branch circuit wiring and cord sets and
power-supply cords.
ARCING
•Continuous luminous discharge of electricity across an insulating
medium.
•Usually accompanied by the partial volatilization of the
electrodes.
• Some arcs are a normal consequence of device operation.
•Certain devices are designed to contain arcs from combustible
surroundings. Other arcs are unwanted.
* For arcs in electrical distribution systems, the insulating medium is an air
gap, wire insulation, or any other insulator used to separate the electrodes or
line and neutral conductors.
* An arc will not jump an air gap and sustain itself unless there is at least
350 V across the gap.
* Therefore, in 120/240 V ac systems, it is difficult for arcing to cause
ignition unless arc tracking occurs, or the electrodes loosely contact each
other causing a sustained arcing fault.
Two basic types of arcing faults

Series arcing faults

Parallel arcing faults
Series arcing faults
•Occur when the current-carrying path in series with the load is
unintentionally broken.
•Arcing may occur across the broken gap and create localized
heating.
•The magnitude of the current in a series arc is limited by the
load.
•The series arcing currents are below the typical circuit
breaker’s ampacity rating (handle rating) and, therefore, would
never trip the conventional circuit breaker either thermally or
magnetically.
*Series arcing can lead to overheating that can be hazardous.
*Examples of conditions that may result in series arcing fault
- loose connections to a receptacle or a wire splice
- a worn conductor from over flexing of a cable.
PARALLEL ARCING
FAULTS
• Occurs when there is an unintentional conducting path between
conductors of opposite polarity.
• Limited by the available fault current of the source and the impedance
of the fault.
• If the fault is of low impedance, the over current device should open.
*When the fault impedance is relatively high, there may be
insufficient energy to open the overcurrent device. This can
cause arcing that can propel particles of molten metal onto
nearby combustibles.
*Examples
short circuit caused by an intermittent contact
line-to-ground arcing fault
•Develop in three stages: leakage, tracking, and arcing.
•Leakage currents normally occur in every electrical wiring system
due to parasitic capacitance and resistance of the cable insulation.
•Leakage current values below 0.5 mA are safe. If maintained in good
condition, the wiring may be used safely for several decades.
• When the wiring is subjected to moisture, conductive dusts, salts,
sunlight, excessive heat, or high-voltage lightning strikes, the
insulation can break down and conduct higher leakage currents.
• As leakage current increases, the surface can heat up and pyrolyze
the insulation. This process, known as tracking, produces carbon
that generates more heat and progressively more carbon.
• This process may continue for weeks, months, or longer without
incident, eventually, sustained arcing may occur.
*Parallel arcing faults are hazardous than series arcing faults, since more
energy is associated with a parallel arcing fault.
*Parallel arcing faults result in peak currents above the handle rating of the
conventional circuit breaker. This may trip the circuit breaker magnetically,
if the impedance of the fault is low and the available fault current is
sufficient.
* But usually, the available fault current is not sufficient to trip the circuit
breaker instantaneously.
ARC CHARACTERISTICS
• High-frequency noise is seen in voltage and current traces.
• There is a voltage drop across the arc.
• Because of the voltage drop across the arc, arcing current is
lower than non-arcing current in the same circuit, except in
cases in which the equipment attempts to compensate for the
difference.
• Rate of rise of arc current is usually greater than that for
normal current.
• In each half cycle, arcing current extinguishes before a
normal current zero and reignites after the normal current
zero, establishing a nearly flat, zero-current section in each
half cycle. These regions “shoulders.”
• The voltage wave looks rectangular.
ARC DETECTION TECHNOLOGY
Two means of detecting hazardous arcs:
1) arc signal detection.
2) ground-fault detection.
Arc signal detection
•Constantly monitor current and/or voltage signals for
distinguishing characteristics of arcs or changes of arc
characteristics.
•The detecting circuit might look for a number of characteristics
or changes that indicate the probable presence of an arc.
•If sufficient numbers of these conditions are present, it declares
that an arc exists and it outputs a signal to cause the AFCI to
open the circuit.
Ground-fault detection
•Detect the imbalance of current between that leaving
the line terminal and that returning in the neutral
conductor. If the imbalance is greater than about 50
mA, the device opens the circuit.
WHERE AFCIs SHOULD BE USED
•The 1999 edition of the US National Electrical Code adopted by
many local jurisdictions, requires AFCIs for receptacle outlets in
bedrooms.
•The requirement is limited to only certain circuits in new
residential construction.
•AFCIs are considered for added protection in other circuits and for
existing homes.
• Older homes with aging and deteriorating wiring systems can
especially benefit from the added protection of AFCIs.
•AFCIs should also be considered whenever adding or
upgrading a panel box while using existing branch circuit
conductors.
•AFCIs would replace the conventional thermal/magnetic
circuit breakers currently used in a panel.
INSTALLING OF AFCI
•Should be installed by a qualified electrician.
•The installer should follow the instructions accompanying
the device and the panel box.

In homes equipped with conventional circuit breakers
rather than fuses, an AFCI circuit breaker may be
installed in the panel box in place of the conventional
circuit breaker to add arc protection to a branch circuit.
TESTING AN AFCI
•AFCIs should be tested after installation to make sure they are
working properly and protecting the circuit.
•AFCIs should be tested once a month to make sure they are
working properly and providing protection from fires initiated by
arcing faults.
•A test button is located on the front of the device.
• The user should follow the instructions accompanying the
device.
•If the device does not trip when tested, the AFCI is defective and
should be replaced.
CONCLUSION
•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.
•The heavy toll on human life and property from electrical fires
provides a clear indication of the need for home builders and
contractors to provide consumers with the safest home possible.
•Educating home buyers on the latest in home protection devices
and similar “after the fact” safety devices.
•New home owners should know what options are available
in the way of home safety, and are encouraged to ask their
builder or electrician about the life-saving capabilities of
AFCIs.
•With the potential to cut the number of electrical fires that
occur each year in half, AFCI technology should not be
overlooked.
THANK YOU
REFERENCES
1. George D. Gregory –”More about arc-fault circuit interrupters”,
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS,
VOL. 40, no. 4, july /august 2004
2. Douglas A. Lee, Andrew M. Trotta and William H- “New
Technology for Preventing Residential Electrical Fires: Arc-
Fault Circuit Interrupters (AFCIs)”
3. John Brooks and Gary Scott- “Arc-fault Circuit Interrupters For
Aerospace Applications”,
4. T. Gammon and J. Matthews, “Instantaneous arcing-fault models
developed for building system analysis,” IEEE/ACM
Transactions in Industry Applications, vol. 37, no. 1, pp. 197–
203, Jan/Feb 2001.