A & E Service Maintenance Co., Inc. Service
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Arc Fault Breaker AFCI Breakers
These devices work similar in theory to the ground fault circuit interrupter (GFCI); however, their purpose is a little different. The arc fault circuit interrupter (AFCI) is used to sense an arc fault. An arc fault occurs when electric current jumps through an air gap between two current carrying or a current and non-current carrying piece of metal. It takes 80 millivolts to jump across an air gap of one 1000th of an inch. This means in theory that an arc occurring at a 125 volt receptacle could span a gap of one and one half inches.

An arc is a high resistance short circuit. For this reason, it is difficult to extinguish the arc once it begins. The temperature within an arc is extremely hot. It has been theorized that arcs occurring at bedroom receptacles have been linked to the eventual fires in residential homes. In 1999, the NEC code panel added a requirement to the code which requires these devices to be used on all 125 volt receptacle circuits in the bedroom. The code panel further revised this code in the 2002 edition to include all 15 and 20 amp 125 volt outlets within the bedroom, which includes smoke detectors, lighting, receptacles, etc. The AFCI device works as a current limiting device disconnecting the source voltage quickly and thereby extinguishing the arc once it occurs.

Our understanding is that these devices are in their infancy stages. Based on their current design, they will not extinguish arcs in every situation. Their design is based on extinguishing parallel arcs not series arcs. A parallel arc is one which is in parallel with the load. Likewise, a series arc is one which might occur when the load is disconnected from the supply such as during switching operations or when a cord cap is pulled from the receptacle while still under load. Niether the series nor the parallel arc are desirable, but the series arc occurs under normal operation. We expect future technology will resolve the problems surrounding these devices, and we plan to stay abreast of the future changes as they occur.

AFCI devices will become standard in new homes, but retrofits may be difficult to perfect. Call us for further assistance in selecting AFCI devices for your applications.

The following downloads are PDF files from Square D further explaining AFCI breakers:

Facts About AFCI Devices
Shared Neutrals and AFCIs
Troubleshooting AFCIs