Although flawed in its execution, the addition of AFCIs to the 2002 Code highlights the importance of arc-fault protection.
Circuit breakers and fuses are effective in preventing fires caused by a bolted-type short circuit or ground fault. However, the amount of current flow in a high-impedance arc is often too low to trip the protection device, creating the potential for a fire. To reduce the number of electrical fires caused by parallel arc faults in branch circuit wiring, the NEC now requires a listed arc-fault circuit interrupter (AFCI) protection device in branch circuit wiring that services dwelling unit bedrooms.
New Code requirements.
In 210.12(A), the 2002 NEC defines an AFCI as “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.” Also note the new wording of 210.12(B). Before, all branch circuits that supplied 125V, single-phase, 15A and 20A receptacle outlets installed in dwelling unit bedrooms had to be protected by an AFCI. Now, AFCIs that protect outlets in dwelling unit bedrooms must be listed to provide protection of the entire branch circuit. (Figure above.)
Because this requirement applies to 125V outlets, AFCI protection isn't required on a 240V circuit serving a baseboard heater or room air conditioner. In addition, a new subsection (B) added to 550.25 requires AFCI protection for all branch circuits that supply 15A and 20A, 125V outlets in bedrooms of mobile homes and manufactured homes.
Muddying the waters is the conflict between circuit breaker manufacturers and wiring device manufacturers that make listed AFCI devices. Circuit breaker manufacturers insist the only acceptable device is the AFCI circuit breaker, but wiring device manufacturers take the position that AFCI receptacles listed to protect the entire branch circuit are equally suited and Code-compliant.
However, the Code has the final say. An AFCI protection device must de-energize and protect the entire circuit from an arc fault. The only device that can do this is an AFCI circuit breaker. Because AFCI receptacle types listed to detect upstream series arc faults will not de-energize the circuit from parallel-type arc faults that may occur upstream of the device, they don't meet the requirement set forth in 210.12.
For the electrician wiring a dwelling unit, it's hard to tell by looking at the bare walls whether a room will be used as a home office or a bedroom. Efficiency apartments can be even more confusing. Such a unit will probably be furnished with a foldout couch used for sleeping, making it look as much like a bedroom as a living room.
If your current wiring practice calls for one branch circuit to supply both lighting and receptacles loads, the 2002 Code will have no effect on you. But if you separate the lighting load from the receptacle load, and place them on individual circuits in dwelling unit bedrooms, you must now install an AFCI circuit breaker for each circuit.
It's important to note that current requirements in the Code for AFCIs are not all-inclusive. At issue is the fact that currently only bedroom circuits must be protected, despite the fact that an arc can occur on any circuit in the occupancy. Nor is the device listed to protect against fires at loose or poor connections that can occur at receptacles, switches, lighting fixtures, and fans, among other things. Anyone installing an AFCI should take these issues into consideration when trying to prevent arc faults.
Although a relatively new piece of protection equipment, AFCIs are no less important than their ground-fault protection counterparts. Industry studies have shown that more than 60% of house fires are caused by faulty fixed wiring, switches, receptacle outlets, and lighting fixtures, so the Code-making panels thought it best to address this problem first. However, as the industry gains experience in working with these devices and AFCIs become more prevalent, further requirements may show up in later versions of the Code.
Sidebar: Rejected Proposals For the 2002 NEC
Require AFCI protection for existing bedroom branch circuits.
Omit AFCI protection for lighting outlets, because light may be needed when an AFCI device operates.
Extend AFCI protection to guest room branch circuits of motels and hotels.
Permit the AFCI receptacle outlet to provide required protection.
Omit AFCI protection for smoke detector circuit conductors.
Delete AFCI requirements completely.
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