In an electrical system a circuit breaker protects the system from overload and short circuit fault. But without this type of fault happening there might be severe arcing in the circuit that cause electrical fire.
The AFCI- Arc fault circuit interrupter circuit breaker is special type of circuit breaker is to protect the circuit from arc happening. If there is a possibility of lethal arc , the breaker will break the circuit like other normal circuit breaker do with a fault.
So general circuit breaker detects and prevents circuit from overload, short circuit condition, over voltage etc. But these does not cover another potential risk “fire by arcing”. In case of a lethal fire due to arcing, circuit breaker might not be tripped. As there might be no fault happened at all but arcing happened already.
It is due to the fact that while arcing the circuit parameters are different. This detection is not included in the normal circuit breakers. An Arc Fault Circuit Interrupter (AFCI) is a circuit breaker detects an electric arc distinguish from normal arc that might cause fire and trips the circuit breaker.
How Arc Fault Circuit Interrupter (AFCI) works:
Detection:The first things is the detection of lethal arcing. This is done by analyzing the circuit parameters like current, voltage with a certain algorithm . So the arcing is detected and the next thing is to distinguish the lethal arcing that might cause fire and normal arcing.An AFCI should not trip during normal arcing conditions, which can occur when a switching happens.
The advanced electronics inside an AFCI breaker detect sudden bursts of electric current in milliseconds; long before a standard circuit breaker or fuse would trip. A “combination AFCI breaker” will provide protection against parallel arcing (line to neutral), series arcing (a loose, broken, or otherwise high resistance segment in a single line), ground arcing (from line, or neutral, to ground), overload protection and short circuit protection.
Generally arcing conditions produces erratic, and often reduced current.
An AFCI must distinguish between a harmless arc that occurs incidental to normal operation of switches, plugs and brushed motors and an undesirable arc that can occur (Wikipedia)
Image courtesy – ecmweb.com/content/basics-arc-fault-protection
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Arc Fault Circuit Interrupter (AFCI) in medium voltage application-
NFPA-70 National electric code: Arc Fault Circuit Interrupter (AFCI)
National electric code 2005 made it more clear that all outlets must be protected despite discussion in the code-making panel about excluding bedroom smoke detectors from the requirement. “Outlets” as defined in the NEC includes receptacles, light fixtures and smoke alarms, amongst other things—basically, any point where electricity is used to power something is an outlet.
As of January 2008, only “combination type” AFCIs will meet the NEC requirement. (Wikipedia)