The definition of arc-fault circuit interrupter given in 210.12(A) explains its function. The basic objective is to de-energize the branch circuit when an arc fault is detected.
Arc-fault circuit interrupters are evaluated in UL 1699, Standard for Arc-Fault Circuit-Interrupters, using testing methods that create or simulate arcing conditions to determine a product's ability to detect and interrupt arcing faults. These devices are also tested to verify that arc detection is not unduly inhibited by the presence of loads and circuit characteristics that may mask the hazardous arcing condition. In addition, these devices are evaluated to determine resistance to unwanted tripping due to the presence of arcing that occurs in control and utilization equipment under normal operating conditions or to a loading condition that closely mimics an arcing fault, such as a solid-state electronic ballast or a dimmed load.
UL 1699 is the standard covering arc-fault devices that have a maximum rating of 20 amperes and intended for use in 120-volt ac, 60-Hz circuits. These devices may also have the capability to perform other functions such as overcurrent protection, ground-fault circuit interruption, and surge suppression. UL 1699 currently recognizes five types of arc-fault circuit interrupters: branch/feeder AFCI, combination AFCI, cord AFCI, outlet AFCI, and portable AFCI.
Placement of the device in the circuit and a review of the UL guide information must be considered when complying with 210.12. The NEC is clear that the objective is to provide protection of the entire branch circuit. (See Article 100 for the definition of branch circuit.) For instance, a cord AFCI cannot be used to comply with the requirement of 210.12 to protect the entire branch circuit.
The type of AFCI required to comply with 210.12(B) was the subject of a revision in the 2005 Code. To expand the level of AFCI protection for cord sets that are plugged into receptacles supplied by AFCI-protected branch circuits, the use of combination-type AFCI devices is required. These devices provide the combined protection required by UL 1699 for branch/feeder and outlet type AFCIs. The product standard requires specific marking on AFCI devices to indicate the type of protection provided. Combination-type AFCIs bear such a marking. Exhibit 210.21 (Exhibit 210.21 is nothing more than a photo of a combination type AFCI fresh from its packaging -- Al) is an example of a circuit breaker that provides combination-type AFCI protection. In addition to the revised type of AFCI protection required, the location of the AFCI device in the circuit now provides a new option. The exception permits the AFCI device to be located at the first outlet supplied by a branch circuit, provided that the wiring method from the circuit overcurrent protective device to the outlet is rigid metal conduit, intermediate metal conduit, electrical metallic tubing, or steel armored cable. These wiring methods afford a higher level of physical protection for branch-circuit conductors. There is no length restriction on the branch-circuit conductors from the OCPD to the first outlet as long as the conductors are contained within one of the wiring methods identified in Exception No. 1.
For the 2008 Code, 210.12(B) requires that AFCI protection be provided for all 15- and 20-ampere, 120-volt branch circuits that supply outlets (including receptacle, lighting, and other outlets; see definition of outlet in Article 100) located throughout a dwelling unit other than outlets installed in kitchens, bathrooms, unfinished basements, garages, and outdoors. Because circuits are often shared between a bedroom and other areas such as closets and hallways, providing AFCI protection on the complete circuit would comply with 210.12. There is no prohibition against using AFCI protection on other circuits or locations other than those now specified in 210.12(B).
