Arc Fault Circuit Interrupters (AFCIs) are required by the National Electrical Code for certain electrical circuits in the home. Questions have been raised regarding their application and even the need for them. Various technical “opinions”, organizational “marketing pitches”, and misinformation is being distributed about AFCIs that further mislead the public about the purpose of the device as a part of overall electrical safety for the public.
Why do we really need AFCIs?
Smoke alarms, fire extinguishers and escape ladders are all examples of emergency equipment used in homes to take action when a fire occurs. An AFCI is a product that is designed to detect a wide range of arcing electrical faults to help reduce the electrical system from being an ignition source of a fire. Conventional overcurrent protective devices do not detect low level hazardous arcing currents that have the potential to initiate electrical fires. It is well known that electrical fires do exist and take many lives and damage or destroy significant amounts of property. Electrical fires can be a silent killer occurring in areas of the home that are hidden from view and early detection. The objective is to protect the circuit in a manner that will reduce its chances of being a source of an electrical fire.
What are arc faults?
The UL® Standard for AFCIs (UL 1699) defines an arcing fault as an unintentional arcing condition in a circuit. Arcing creates high intensity heating at the point of the arc resulting in burning particles that may over time ignite surrounding material, such as wood framing or insulation.
The temperatures of these arcs can exceed 10,000 degrees Fahrenheit. Repeated arcing can create carbon paths that are the foundation for continued arcing generating even higher temperatures.
How is an arc fault detected?
Unlike a standard circuit breaker detecting overloads and short circuits, an AFCI utilizes advanced electronic technology to “sense” the 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 the use of advanced electronic technology 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 create 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 measure constantly for the normal and dangerous arcing conditions.
Types of Breaker AFCI
Arc Fault Circuit Interrupter (AFCI)
AFCIs are intended to mitigate the effects of arcing faults by functioning to de-energize the circuit when an arc-fault is detected. AFCIs are required by the NEC® to be a listed product. This means that they must be evaluated by a nationally recognized testing laboratory to the national standard for AFCIs (UL 1699). NEC 210.12 establishes the requirement to use AFCIs. Protection is required for branch circuits in locations as specified in this NEC® rule.Branch Feeder AFCI
A device intended to be installed at the origin of a branch circuit or feeder, such as at a panelboard. The branch/feeder AFCI provides for detection of arcing faults that can occur line-to line, line to neutral and line to ground.
To be able to handle shared neutral circuits (a common application in older homes), a two-pole AFCI can be used. This will accommodate the three-wire circuit arrangement used in shared neutral applications.
In addition to the protection provided by the Branch Feeder AFCI, the Combination AFCI provides for series arc detection down to 5 amperes. This series arc detection is beneficial to detect lower level arcing in both branch circuits and power supply cords. Combination AFCI protection is required by the NEC® as of January 1, 2008.
Breaker AFCI and GFCI Protection
An AFCI can be used in conjunction with GFCI protection to provide both arcing fault protection as well as 5mA ground fault (people) protection. A common way to provide both types of protection is to use an AFCI circuit breaker and a GFCI receptacle. AFCI's can also incorporate 5mA GFCI protection into the same package. This solution for AFCI breaker and GFCI on the same circuit can be useful where the circuit design requires both types of protection or where the installer (or user) wants to have both types of protection.
What is the difference between a ground fault and an arcing fault?
A ground fault is when electricity “leaks” to ground via water, moisture or some other method when an appliance or other electrical device is used. A ground fault circuit breaker or GFCI outlet is designed to “sense” when that leakage is occurring and shut off the power to the circuit or outlet. An arc fault is an “arcing condition” that takes place when electricity is "jumping" or “arcing” from one conductor to another due to damaged wiring, either in the wall or on the electrical products power cord. These arcs have the potential to initiate fires after repeated arcing events. The Arc Fault Circuit Interrupter is designed to shut off the power during these events.
An AFCI does not replace a GFCI. They are two different technologies even though both offer protection from electrical hazards. When in doubt, contact a qualified electrician as to their application and what is required by your local electrical code.