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What is an AFCI?

Unlike a standard circuit breaker detecting overloads and short circuits, an AFCI utilizes state-of-the-art electronics to “sense” different arcing conditions. While there are different technologies employed to measure arcs by the various AFCI manufacturers, the end result is the same, detecting parallel arcs (line to line, line to neutral and line to ground) and/or series arcs (arcing in series with one of the conductors).


How does arc fault detection work?

In essence, the detection is accomplished by using electronics to monitor the circuit for the presence of “normal” and “dangerous” arcing conditions. Some equipment in the home, such as a motor driven vacuum cleaner or furnace motor, naturally creates arcs. This is considered to be a normal arcing condition. Another normal arcing condition that can sometimes be seen is when a light switch is turned off and the opening of the contacts creates an arc.

A dangerous arc, as mentioned earlier, occurs for many reasons including damage of the electrical conductor insulation. When arcing occurs, the AFCI analyzes the characteristics of the event and determines if it is a hazardous event. AFCI manufacturers test for the hundreds of possible operating conditions and then program their devices to monitor constantly for the normal and dangerous arcing conditions.

Where do I need to use AFCIs?

Starting January 1, 2002, The National Electrical Code , Section 210-12, required that all branch circuits supplying 125V, single phase, 15 and 20 ampere outlets installed in dwelling unit bedrooms be protected by an arc-fault Circuit interrupter (AFCI). This is being expanded, see NEC 2008 below, to include pretty much every room in the house with the exception of laundries, kitchens, bathrooms, garages, and unfinished basements. The NEC selected to require them on bedroom circuits first because their study showed many home fire deaths were related to bedroom circuits.

An AFCI breaker will shut off a circuit in a fraction of a second if arcing develops. The current inside of an arc is not always high enough to trip a regular breaker as described earlier. You may have noticed a cut or worn piece of a cord or a loose connection in a junction box or receptacle arcing and burnt without tripping the regular breaker. As you can guess this is a major cause of fires in a dwelling. There is a difference between AFCIs and GFCIs. AFCIs are intended to reduce the likelihood of fire caused by electrical arcing faults; whereas, GFCIs are personnel protection intended to reduce the likelihood of electric shock hazard Don't misunderstand, GFCIs are still needed and save a lot of lives.

Dual function devices that include both AFCI and GFCI protection in one unit are on the horizon. AFCIs can be installed in any 15 or 20 ampere branch circuit in homes today and are currently available as circuit breakers with built-in AFCI features. In the near future, other types of devices with AFCI protection will be available. If a GFCI receptacle is installed on the load side of an AFCI it is possible for both the AFCI and the GFCI to trip on a fault if the current exceeds the limit for both devices. It is also possible for the AFCI to trip and the GFCI to not trip since the two devices could race each other. However, in no case is safety compromised. At first the cost for AFCI will be high. Expect to pay around $35 for each AFCI at Home Depot. The cost is expected to drop as these become more heavily used.

NEC 2008 Section 210-12

(a) Definition: An arc-fault circuit interrupter is a device intended to provide protection from the effects of arc faults by recognizing characteristics unique to arcing and by functioning to de-energize the circuit when an arc fault is detected.

(b)Dwelling Units. All 120-volt, single phase, 15- and 20-ampere branch circuits supplying outlets installed in dwelling unit family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, or similar rooms or areas shall be protected by a listed arc-fault circuit interrupter, combination-type, installed to provide protection of the branch circuit.  

Does my fire alarm circuit need an AFCI breaker?

Short answer - yes.  For residential wiring, fire alarms should be on there own branch circuit, with no other outlets or lights, and since they extend into the bedrooms they need to be on an AFCI breaker per the latest NEC requirements. 


What is the difference between a combination Type AFCI and a Branch/Feeder AFCI?

Combination Type AFCI provides protection against all three types of arcs (series, line-to-neutral, and line-to-ground). The Combination Type meets all the 1999 and later NEC requirements. It is specifically required by the 2005 NEC beginning January 1, 2008.

The original Branch/Feeder AFCI’s provided protection against only two types of arcs (line-to-neutral and line-to-ground). It could used to meet the requirements of the 1999-2002 NEC and the 2005 NEC until January 1, 2008.

Does the term "Combination" mean that GFCI protection is included with the AFCI breaker?

No, it only means that the device protects against all three types of arcing. Any device that would include GFCI protection would be referred to as a dual function device.  


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