
AFCI circuit breaker, or arc fault circuit interrupter, is a special type of circuit breaker that is engineered to sense and interrupt dangerous electrical arcs and associated faults in the circuit before a fire hazard occurs. It is usually installed in the electrical panel, which protects the electrical circuit from short circuit, overloading, and especially senses the arc faults in the circuit and interrupts thus saving the wiring and the associated equipment. The interruption of the circuit after sensing an arc fault is instantaneous, so that overheating, sparking, and potential fire hazard can be avoided.
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Working Principle of AFCI circuit breaker
Detection of Arc fault: The waveform of an arc fault is irregular and different from that of a regular load current. The arc often produces high-frequency noise and current spikes in the circuit, mostly above 100Khz. These arcs mostly occur because of a loose connection or a broken conductor (Series Arc) or between the live and ground wires because of bad insulation or frayed wires intermittently touching (Parallel Arc). The AFCI circuit breaker continuously monitors the waveform of the circuit and instantaneously trips the breaker if it finds any such fluctuation in the waveform.
Sophisticated Electronics: Unlike standard circuit breakers, AFCI circuit breakers have a built-in electronic circuit. The current sensors (usually Hall-effect sensors) monitor the current flowing into the circuit and feed the current conditioning stage, which filters and amplifies the signal. This signal enters the microprocessors or digital signal processor (DSP) that constantly analyzes the electrical waveform for any abnormality.
As an arc fault produces high frequency, rapid change in amplitude with the zero voltage crossing point being inconsistent, the processor uses an algorithm and pattern recognition to compare the signal to stored arc fault signatures. The sophisticated filters in the electronic circuit prevent the circuit breaker from tripping because of harmless faults like the start of the motor or the switching operation of the light.

Automated Tripping: After the electronics in the AFCI circuit breaker agree to arc fault characteristics, it activates the tripping mechanism of the breaker. The mechanical contacts of the breaker immediately open up, restricting current flow to the circuit. The rapid disconnection is essential because arcing heats up the circuit wiring, which can potentially ignite the combustible substances around it, creating an electrical fire.
Types of AFCI circuit breakers
Branch Feeder AFCI circuit breaker: It is the first AFCI circuit breaker that was designed for the protection of a complete branch circuit from parallel arc faults, which are mostly line-to-line faults or line-to-ground faults. It is installed in the electrical panel and provides the downstream protection to outlets and connected devices. While the branch feeder AFCI was very effective in protecting of circuit from parallel arc faults, it was poor in sensing the series arc faults that are loose connections and broken conductors. It is because of this limitation, these are mostly replaced in modern electrical applications.
Combination AFCI: A combination AFCI circuit breaker is one that overcomes the branch feeder AFCI by offering protection from both parallel and series faults. The faults occurring between two conductors are parallel faults, while the faults occurring in a single conductor or a damaged one is the series fault. Providing protection against both increases the safety level against electrical fires. It is installed in the main electrical panel and provides protection to all of the downstream circuits. As per the national electrical code, combination AFCI circuit breakers are now mandatory in new construction, making them the standard for all upcoming construction.
Dual protection circuit breakers: These AFCI circuit breakers offer dual functions packed into one unit. The one is arc fault protection, which protects against arc faults and fire hazards; the second is ground fault protection, which protects humans from electrical shock by detecting ground faults. The dual protection is required in places where both fire and the chance of electrical shock are present. It also eliminates the need for two separate breakers for achieving both functions of AFCI and GFCI.
Outlet branch circuit (OBC) AFCI breaker: These breakers are designed to be placed at the first outlet of the branch circuit instead of the main panel. It protects the device connected to the outlet from both parallel and series arc faults. This type of breaker is used in retrofitting arrangements where changing the main panel breaker is not practical. They provide the needed arc fault protection near the load as it is installed in the outlet. Also, it makes the upgradation of old circuits, with arc fault protection, easier.
Advantages of AFCI circuit breakers.
Protection against electrical fires: AFCI circuit breakers provides protection against electrical arcs which standard circuit breaker cannot detect.
Enhanced protection: AFCI circuit breakers other than offering electrical arc protection which nullifies risks of electrical fire, also provides standard overloading and short circuit protection to downstream circuits.
Dual protection: Some types of AFCI breakers provides dual protection of the electrical circuits. Along with standard protection of overloading and short circuit condition, electrical arc fault protection and ground fault protection are the added advantages of these circuit breakers.
Limitations of AFCI breakers:
Expensive: These breakers are more expensive than the standards circuit breakers because of the advanced electronic circuitry and microprocessors that it houses for sensing and tripping the breaker.
Nuisance Trips: These breakers although provides specialised protection to downstream circuit but if connected wrong, can cause unwanted tripping of the circuit. Also, if incompatible devices are connected to these breaker, it will result in nuisance tripping of the breaker.
Proper workmanship: Although these breakers adds layer after layer of protection to electrical circuit, they still requires proper workmanship. Loose connection, undersized conductors and improper insulation has to be properly addressed without which the circuit will still be under risks and prone to hazard.
What is the difference between AFCI & GFCI circuit breakers?
Both these circuit breakers are functionally different in perspective of circuit protection. AFCI protects the circuit against electrical arc and its consequences like fire, while GFCI protects against ground faults and its consequences which is basically electrical shocks.
What is AFCI 6 Foot rule?
As per the NEC, a branched electrical circuit whose extension is less than 6 foot with no outlets can opt for no AFCI circuit breakers.
How to identify a AFCI outlet?
AFCI and GFCI circuit breakers have a test and reset button attached to its body.
What is the full form of AFCI?
The full form of AFCI is Arc Fault Circuit Interrupter.
This article is a part of the Switchgear, where other articles related to switchgear are discussed in details.