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.”
Arc-Fault
Circuit Interrupters (AFCIs)
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 protect 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. 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 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.
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 magnitude and time period of a particular half
cycle are required.
An Arc-Fault
Circuit Interrupter should not trip during regular current conditions. 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 Circuit Interrupters
Here
different types of AFCIs are available depends 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.
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.
Cord AFCI
The cord AFCI
is also a plug-in device that is connected to the receptacle outlet and often
used to protect the connected power cord.Thus,
this is all about Arc-Fault Circuit Interrupters and its functions.
We hope
that you have got a better understanding of this concept.
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