Arc Fault Circuit Interrupters and the 2002 National Electrical Code
Arc Fault Circuit Interrupters and the 2002 National Electrical Code.
By Mike Holt
For EC&M Magazine
Wiring and equipment installed in accordance with the National Electrical Code will be protected against arcing faults to a certain degree by a circuit breaker, fuse, or ground-fault circuit-interrupter. Circuit breakers and fuses are reasonably effective in preventing fire causes for conditions under which they are designed to operate. That is, when a bolted short circuit or ground fault occurs the circuits overcurrent protection device opens, fires are frequently prevented. (Graphic)
However, the current flow of a high-impedance arc is often too low to cause operation of the protection device, and a fire could occur. (Graphic)
To help reduce the hazard of electrical fires from a parallel arcing fault in the branch circuit wiring, the NEC requires a listed AFCI protection device be installed in branch circuit wiring in dwelling unit bedrooms.
Authors Comment: See the Back to Basics article for information on what causes an arc and how a AFCI protection device operates.
The 1999 NEC Rule:
210-12. Arc-Fault Circuit-Interrupter Protection
(a) Definition. An arc-fault circuit interrupter is 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.
(b) Dwelling Unit Bedrooms. All branch circuits that supply 125-volt, single-phase, 15- and 20-ampere receptacle outlets installed in dwelling unit bedrooms shall be protected by an arc-fault circuit interrupter(s). This requirement shall become effective January 1, 2002. (Graphic)
The 1999 NEC Rule
210.12 Arc-Fault Circuit-Interrupter Protection.
(A) Definition. An arc-fault circuit interrupter is 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.
(B) Dwelling Unit Bedrooms. All branch circuits that supply 125-volt, single-phase, 15- and 20-ampere receptacle outlets installed in dwelling unit bedrooms shall be protected by an arc-fault circuit interrupter listed to provide protection of the entire branch circuit.
Strike through indicates text that was deleted and underline text indicates text that was added to the 2002 NEC. (Graphic)
Authors Comment: The 125 V limitation to the requirement means that AFCI protection would not be required for a 240 V baseboard heater or room air conditioner. For more information, visit http://www.mikeholt.com/articlecategories.php, go to the Miscellaneous section and visit my AFCI links.
The intent of the change from the 1999 NEC is that arc fault protection be provided for all branch circuits that supply 125-volt, single-phase, 15- and 20-ampere outlets, not just receptacle outlets. In addition, the AFCI must be listed so that it will protect the entire branch circuit by de-energize the circuit when an arc fault is detected.
Controversy exists between circuit breaker manufactures and wiring device manufactures that make listed AFCI devices. The circuit breaker manufacture insists that the only acceptable device is the AFCI circuit breaker. Wiring device manufactures take the position that AFCI receptacles listed to protect the entire branch circuit should be suitable and Code compliant.
Both make excellent arguments, but the NEC is very specific. It requires the AFCI protection device to de-energize the circuit and protect the entire circuit from an arc fault. The only device that can de-energize the circuit when an arc fault is detected is the AFCI circuit breaker. AFCI receptacles of the type listed to detect upstream series arc faults will not de-energize the circuit from parallel type arcing faults that may occur upstream of the device. Therefor they cannot be used to meet the NEC requirement of 210.12. (graphic)
At the time a dwelling unit is wired, it is hard to tell from looking at the bare walls whether a room will be used as a home office or a bedroom. Also, if you are looking at an efficiency apartment, a room may well be furnished with a foldout couch that is used for sleeping on every night, making it look as much like a bedroom as a living room.
If you are in the practice of using one branch circuit for both lighting and receptacles, the 2002 Change will have no effect. But, the practice of separating the lighting from the receptacle circuits in dwelling unit bedrooms will now require two AFCI circuit breakers, or youll place them all on the same circuit.
A new subsection (B) was added to 550.25 to require all branch circuits that supply 15 and 20A, 125V outlets in bedrooms of mobile homes and manufactured homes to be protected by arc-fault circuit interrupter.
Why is AFCI protection only required for dwelling unit branch circuits? The NEC Code wanted the industry to gain experience with these devices in bedroom circuits so that in the future their usage might be expanded to other rooms and facilities that could benefit by the added protection to provide. Studies have shown that over 60 percent of fires are from causes in the fixed wiring, switches, receptacle outlets and lighting fixtures that are part of the fixed electrical system of a residence.
The following proposals for the 2002 NEC were all rejected:
The U. S. Consumer Product Safety Commission request that existing bedroom branch circuit be protected by an AFCI when the service equipment is replaced.
Omit AFCI protection for the lighting outlets, because light may be needed when the AFCI device operates.
Extend AFCI protection guest room branch circuits of motels and hotels.
Permit the AFCI receptacle outlet to provide the required protection.
Omit AFCI protection for the smoke detector circuit conductors.
Delete the AFCI requirement completely.
Common Questions about AFCIs
Q1. What happens when an appliance has a locked rotor condition (bedroom
window air-conditioner)? Will the AFCI breaker respond?
A1. No and Yes. The waveform signature of lock rotor current is not typical of an arc fault, so the AFCI will not respond, but once the motor winding shorts out, the overcurrent protection device will open.
Q2. Will there be lots of nuisance tripping of these devices?
A2. Honestly there has not been sufficient experience in the field to answer this question, but what might appear to be a nuisance tripping condition might be an actual arc fault. The industry will have to learn how to troubleshoot these failures.
Q3. Will a AFCI prevent fires from loose connections at terminals or splicing
A3. No, this product is not designed to protect against this type of series (glowing) fault.
Q4. Are there any AFCI/GFCI combination breakers?
If you have any comments or suggestions, please let me know. Mike@MikeHolt.com.
Copyright © 2002 Mike Holt Enterprises,Inc.