ARC-FAULT CIRCUIT INTERRUPTER(AFCI)

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ARC-FAULT CIRCUIT INTERRUPTER(AFCI)

• Presented by
• Honey Baby George
• S7,EEE
• Roll no-21

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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

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INTRODUCTION
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• 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. 

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• 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.

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• A circuit breaker
• protects electrical branch circuit wiring.
• reduce the risk of fire from overheating.
• Circuit protection devices 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.

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• 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.

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ARC FAULT CIRCUIT INTERRUPTER
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• 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.

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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
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AFCI WORKING
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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.
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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.
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• 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.

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• 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.

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• 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.

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TYPES OF AFCIs
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• Branch/Feeder AFCI
• Outlet Circuit AFCI
• Combination AFCI

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• 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.

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• It may be a circuit- breaker-type device or a
  device in its own enclosure mounted at or near a
  panel board.

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• 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)
• against the unwanted effects of arcing.

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• 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.

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ARCING
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• 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.

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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.
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• Two basic types of arcing faults
• Series arcing faults
• Parallel arcing faults

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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.

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• The series arcing currents are below the typical
  circuit breakers ampacity rating (handle rating)
  and, therefore, would never trip the conventional
  circuit breaker either thermally or magnetically.

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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.
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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.

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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

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• 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.

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• 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.

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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.
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ARC CHARACTERISTICS
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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.
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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.
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ARC DETECTION TECHNOLOGY
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• Two means of detecting hazardous arcs
• arc signal detection.
• ground-fault detection.

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• 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.

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• 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.

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WHERE AFCIs SHOULD BE USED
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• 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.

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• 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.

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Installing of afci
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• Should be installed by a qualified electrician.
• The installer should follow the instructions
  accompanying the device and the panel box.

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• 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.

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TESTING AN AFCI
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• 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.

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CONCLUSION
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• 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.

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• 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.

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THANK YOU
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• REFERENCES
• George D. Gregory More about arc-fault circuit
  interrupters, IEEE TRANSACTIONS ON INDUSTRY
  APPLICATIONS, VOL. 40, no. 4, july /august 2004
• Douglas A. Lee, Andrew M. Trotta and William H-
  New Technology for Preventing Residential
  Electrical Fires Arc-Fault Circuit Interrupters
  (AFCIs)
• John Brooks and Gary Scott- Arc-fault Circuit
  Interrupters For Aerospace Applications,
• 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. 197203,
  Jan/Feb 2001.