Arc-fault circuit interrupter (AFCI) protection was originally proposed for the 1996 National Electrical Code (NEC) by the Electronic Industry Association, but it failed to receive enough votes during the adoption process. The electronic and electrical industry spent time and money and used extremely qualified technical experts to develop and test AFCI circuit breakers. The 1999 NEC incorporated this safety device in new Section 210.12, which consisted of two subsections. Subsection (a) provided a definition of the AFCI, and subsection (b) provided the installation location requirements but established an effective date for application on Jan. 1, 2002. Since its inclusion in the 1999 NEC, AFCI requirements in 210.12 have been modified for every NEC cycle, including the new changes in the 2011 NEC. A close examination of the newest changes, two exceptions and a modified (B), covering branch circuit extensions or modifications, will help NEC users.
All 120-volt, single-phase, 15- and 20-ampere (A) branch circuits supplying outlets 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 combination-type AFCI. Where any of these branch circuits are modified, replaced or extended, they shall be protected by either a listed combination-type AFCI located at the origin of the branch circuit, such as a circuit breaker, or by a listed outlet branch-circuit-type AFCI located at the first receptacle outlet of the existing branch circuit. For example, if a branch circuit that was installed before AFCI protection was required in a dwelling unit must be extended to supply a new receptacle, the installer must locate the homerun to the first receptacle in the existing circuit and replace this receptacle with an outlet-type AFCI device. This outlet-type AFCI device provides protection for the circuit from the first receptacle to the last receptacle, even though the homerun will not be protected. Of course, the installer could also install an AFCI circuit breaker at the origin of the branch circuit, assuming the circuit breaker is available as an AFCI breaker. Since electrical manufacturers do not have outlet AFCI devices available in the market yet, the installer would have to install a combination-type AFCI circuit breaker.
A combination AFCI circuit breaker will provide arcing fault protection for series faults of 5A or more and parallel faults of 75A or more. Outlet-type arc-fault branch-circuit devices have been investigated to provide protection of downstream branch-circuit wiring, cord sets and power supply cords against the unwanted effects of series and parall-el arcing faults. These devices also can provide some limited upstream branch-circuit protection. Some of these outlet AFCI devices can have feed-through connections but only where the device is listed for this function.
There were two exceptions added to 210.12 in 2011 NEC, both dealing with outlet--style AFCI devices. For Exception No. 1, rigid metal conduit, intermediate metal conduit, electrical metal tubing, Type MC cable or steel armored AC cable, all in compliance as an acceptable equipment-grounding conductor, can be installed between the branch circuit panelboard and the first outlet in the circuit. This first outlet box must be metal, and any junction boxes between the panelboard and the first outlet also must be metal boxes. Where these previous requirements are accomplished, an outlet-type AFCI can be installed at the first outlet to provide protection for the remainder of the circuit. The metal raceways or cables previously described are protecting the part of the circuit from the panelboard to the first outlet from damage.
For the second exception, if a listed metal or nonmetallic conduit or tubing encased in not less than 2 inches of concrete from the panelboard to the first outlet provides the physical protection for the circuit up to that first outlet box, then an outlet-type AFCI device can be installed to provide protection for the remainder of the circuit. Both of these exceptions are based on the assumption that outlet-type AFCI devices are available on the market. Where these outlet devices are not available, the only option is to install the listed combination-type AFCI circuit breaker. Where an older panelboard provides power to a branch circuit, a new panelboard, with space for two or four circuits, or more, can be installed. The new panelboard will accept AFCI circuit breakers and provide arc-fault protection for the entire branch circuit.
With proper branch-circuit design and attention to detail, arc-fault protection can be installed for dwelling unit branch circuits that will trip the AFCI device before a fire starts. Check with the local electrical supply in your area for the availability of outlet-type AFCIs.
ODE is a staff engineering associate at Underwriters Laboratories Inc., based in Peoria, Ariz. He can be reached at 919.949.2576 and firstname.lastname@example.org.