Mon. Dec 6th, 2021

HSSE WORLD

Health, Safety, Security and Environment

Photo of the day: Arc-Fault Circuit Interrupters (AFCI)

8 min read

Home fires are more deadly and costly than ever. While the number of total fires and fire injuries is decreasing, property damage and fire deaths are on the rise. Each year arc-faults, caused by worn and inadequate wiring, overburdened circuits, outdated technology, and aging electrical systems, start more than 35,000 home fires causing over 1,130 injuries, 500 deaths, and $1.4 billion in property damage. 

An arc fault circuit interrupter (AFCI) is a circuit protection device designed to protect against fires caused by arcing faults in electrical wiring. An arc fault circuit interrupter is defined as “a device proposed to provide protection from the effects of arc faults by recognizing arcs and by functioning to de-energize the circuit when an arc fault is detected.”

The photo of today will outline the meaning of AFCI and the common causes of Arc-Faults in addition to the different types of Arc-Fault Protection

What is an arc fault?

An arc fault is a dangerous electrical problem caused by damaged, overheated, or stressed electrical wiring or devices. 

Arc faults can occur when older wires become frayed or cracked, when a nail or screw damages a wire behind a wall, or when outlets or circuits are overburdened.

Common Causes of Arc-Faults:

  • Damaged electrical wiring 
  • Wiring damaged by screws or nails
  • Wiring damaged by doors
  • Damaged electrical insulation
  • Overheated cords under carpets or rugs
  • Damaged or loose connections
  • Cords and plugs damaged by furniture

Arc-Fault Protection is Required in:

  • Bedrooms
  • Closets
  • Kitchens
  • Laundry areas
  • Living rooms
  • Family rooms
  • Rec rooms
  • Parlors, libraries, or dens

What are arc fault circuit interrupters, or AFCIs?
Arc fault circuit interrupters, or AFCIs, are devices that provide a higher level of protection by detecting hazardous arcing conditions and shutting down the electricity before a fire can start

Theoretically, an arc is defined as a Continuous illumination discharge of electricity across an insulating medium, usually supplemented by the partial volatilization of the electrodes. An AFCIs are designed into conventional circuit breakers combining traditional overload and short-circuit protection with arc fault protection.

The AFCI circuit interrupters provide protection for branch circuit wiring and limited protection for power cords and extension cords. The AFCI circuit breakers have a test button and look similar to the GFCI circuit breakers shown in the below figure. Generally, AFCIs require monthly testing to notify the user that the AFCI is functioning properly.

There are several probable reasons an arc fault may occur, as given below.

  • Improper installation or stabbing of a wire with a screw, nail during installation or maintenance of the electrical system.
  • Damaging of extension or appliance cords by vacuum cleaners, door furniture or an appliance has been positioned on the cord.
  • The advanced age of extension or appliance cords, or even wiring in the walls, which can over time experience worn or cracked insulation.
  • Loose connections in outlets, switches, and light fixtures.
  • Appliance cords damaged by heat, kinking, impact or over-extension, spillage of liquid.

Parallel and Series ARC Faults

Any of the above circumstances, which we discussed above can result in a parallel or series arc. The parallel arc fault arises, when the current flows through damaged insulation from one conductor to another conductor, producing a short circuit that is too weak to be detected by the circuit breaker.

A Series arc fault arises, when a single wire is damaged and cannot tolerate the current, causing the current to arc from the conductor into the insulation. This leakage current can burn and eventually burn the insulation.

Parallel ARC and Series ARC

How Arc-Fault Circuit Interrupters Work

The AFCI circuitry always monitors the current flow through the AFCI. The Arc-Fault Circuit Interrupters use detection circuitry 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.

The arcs produce a current signature or waveform. The faulty arc can produce a non-periodic waveform. Various methods for the detection of fault arcs include looking at certain frequencies, discontinuities, and variations in the current waveform. For detection, both the magnitude and time period of a particular half cycle are required.

An Arc-Fault Circuit Interrupter should not trip during regular current conditions. The below illustration is a block diagram of a single-pole AFCI circuit breaker.

Single Pole AFCI Circuit Breaker

The AFCI electronics can function independently from the conventional circuit breaker. The conventional circuit breaker has thermal and instantaneous sensing functionality. Using a load current sensor, the AFCI electronics detect the current flow from the load terminals.

The load current sensor can be either a resistive or a magnetic sensor. The load current sensor’s output is fed into an arc signature filter that passes frequency components of arcing waveforms while rejecting other power line frequencies.

The arc signature filter output is amplified and fed into a logic circuit that determines that any unsafe condition exists in the current flow. As discussed before, both amplitude and time period are used to detect the unwanted arcing condition.

If the logic determines that the load must be deactivated, a signal is fed to a TRIAC used to energize a solenoid that opens the circuit breaker contacts. A test circuit is provided to ensure that the arc fault detection circuit is functioning properly or not.

A test button functionality is used to generate a signal that is similar to an arcing output waveform of the load current sensor. The test button will deactivate the circuit if the device is functioning properly.

Types of Arc-Fault Protection:

  • A listed combination-type AFCI circuit breaker 
  • A listed outlet branch-circuit-type AFCI receptacle
  • A listed outlet branch-circuit-type AFCI receptacle in combination with a listed branch-circuit overcurrent device

Types of Arc Fault Circuit Interrupters

AFCI breakers and receptacles protect all downstream wiring and appliances from arc faults. Receptacles should be installed at the first outlet box of a circuit. 

Here different types of AFCIs are available depending upon their viable applications.

Outlet Circuit AFCI

It is intended to provide protection to branch circuit wiring, power supply cords, and cord sets connected to it against the unwanted effects of arcing.

Outlet circuit AFCI
Branch/ Feeder AFCI

These are installed at the origin of the feeder or branch circuit. It is intended to provide protection to the feeder or branch wiring.

Combination AFCI

The combination Arc-Fault Circuit Interrupter combines both the features of the OC and B/F. It is intended to provide protection to protect the appliance cords, extension cords, branch circuits, and feeder wiring.

A typical combination Arc-Fault Circuit Interrupter provides

  • Series arc fault protection
  • Parallel arc protection
  • Ground protection
  • Short circuit protection
  • Overload protection
Portable AFCI

This is a plug-in device that is typically connected to the receptacle outlet and has one or more protected outlet. It is intended to provide protection to the connected extension cords and appliances.

Portable AFCI

Cord AFCI

The cord AFCI is also a plug-in device that is connected to the receptacle outlet and is often used to protect the connected power cord.

Cord AFCI

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Arc-Fault Circuit Interrupters (AFCI)


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