ARC-FAULT CIRCUIT INTERRUPTER(AFCI)

Presented by

Honey Baby George

S7,EEE

Roll no-21

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

CONTENTS

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)

against the unwanted effects of arcing.

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

•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.

Series arcing faults

•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.