Arc Fault Circuit Interrupters

Arc   Fault Circuit Interrupters (AFCI) are a special type of circuit breakers   designed to detect and respond to potentially dangerous electrical arcs in home branch wiring.    

What is an Arc?    

When an electric current crosses an air gap from an energized component to a    grounded component, it produces a glowing plasma discharge known as an arc.  For example a bolt of lightning is a very large, powerful arc that crosses the atmospheric gap from an electrically charged cloud to the    ground or another cloud.  Just as lightening can cause fires, arcs produced by domestic wiring are capable of producing high levels of heat    that can ignite their surroundings and lead to structure fires.     

How do they work?

AFCIs   function by monitoring the electrical waveform (sine wave) and promptly    opening (interrupting) the circuit they serve, if they detect changes in    the wave pattern that are characteristic of a dangerous arc.  They    also must be capable of distinguishing safe, normal arcs such as those    created when a switch is turned on or a plug is pulled from a receptacle,   from arcs that can cause fires.  An AFCI can detect, recognize and    respond to very small changes in wave patterns.  AFCIs also test for    ground fault in the 70 – 100 milliamp range and for amperage overload. 

Where are arcs likely to form?

Arcs can form where wires are improperly installed or when insulation becomes damaged.  In older homes wire insulation tends to crystallize as it ages, becoming brittle and prone to cracking and chipping.  Damaged insulation exposes the current-carrying wire to its surroundings, increasing the chances that an arc may occur.      

Situations in which arcs may be created:      

Electrical cords damaged by vacuum cleaners or trapped beneath furniture or doors

Damage to wire insulation from nails or screws driven through walls

Appliance cords damaged by heat, natural aging, kinking, impact or over-extension

Spillage of liquid

Loose connections in outlets, switches and light fixtures

Where are AFCIs required?

In Corpus Christi the current code calls for AFCI protection in the bedrooms   only.  The 2008 National Electric Code, which the city of Corpus Christi has not yet adopted, calls for AFCI protection in all habitable rooms.  

Arc Faults vs. Ground Faults

It is important to distinguish AFCI devices from Ground Fault Circuit Interrupters (GFCI) devices.  GFCIs detect ground faults, which occur    when current leaks from a hot (ungrounded) conductor to a grounded object    as the result of a short circuit.  This situation can be hazardous    when a person unintentionally becomes the current’s path to the    ground.  GFCIs function by constantly monitoring the current flow between the hot and neutral (grounding) conductors, and activate when they    sense a difference of 4 – 6 milliamps or more.  To put this in context a current of 100 – 200 milliamps will cause death.  A GFCI will not prevent you from a shock but will prevent death.  Thus, GFCIs are intended to prevent personal injury due to electric shock, while AFCIs prevent personal injuries and property damage due to structure fires.     

In summary AFCIs are designed to detect small arcs of electricity before they have a chance to lead to a structure fire.  AFCIs are also a very good remedy for aluminum wiring.

Randy Farrar Inspection Services, LLC

Professional Inspector License #7846

FHA Fee Inspector ID #G511

361-816-5781