ARC-FAULT CIRCUIT INTERRUPTER(AFCI)

1. ARC-FAULT CIRCUIT INTERRUPTER(AFCI) Presented by Honey Baby George S7,EEE Roll no-21

2. CONTENTS Introduction Arc fault Circuit Interrupter (AFCI) AFCI Working Types of AFCIs Arcing Where AFCI should be used Installing AFCI Testing AFCI Conclusion References

3. INTRODUCTION

4. 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. 

5. 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.

6. 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.

7. 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.

8. ARC FAULT CIRCUIT INTERRUPTER

9. 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.

10. 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

11. AFCI WORKING

12. *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.

13. *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.

14. 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.

15. 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.

16. 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.

18. TYPES OF AFCIs

19. Branch/Feeder AFCI Outlet Circuit AFCI Combination AFCI

20. 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.

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

22. 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.

23. 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.

24. ARCING

25. 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.

26. * 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.

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

28. 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.

29. 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.

30. *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.

31. 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.

32. *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

33. 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.

34. 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.

35. *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.

36. ARC CHARACTERISTICS

37. • 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.

39. • 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.

40. ARC DETECTION TECHNOLOGY

41. Two means of detecting hazardous arcs: • arc signal detection. • ground-fault detection.

42. 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.

43. 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.

44. WHERE AFCIs SHOULD BE USED

45. 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.

46. 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.

47. Installing of afci

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

49. 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.

50. TESTING AN AFCI