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ARC-FAULT CIRCUIT INTERRUPTER(AFCI)
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.
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
*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. 
* 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 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
*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.
*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.