AFCI Questions and Answers
By Mike Holt
Would it be possible for you to give more information on how the tests were conducted?
A typical receptacle installed in a metal and nonmetallic box mounted on wood studs with drywall. The hot wire just touching the screw on the receptacle, it was move around so that it began a very small arc when the 1,500W heater load was on. In less than one hour the receptacle and the wiring in the box would melt. The AFCI opened because of an arc fault (line-to-neutral) on one case (when the peak current of a half-cycle exceeded 50A, three times in a row) and it was the Ground Fault Interrupter (GFI) that opened in the other. In both of these examples, the arc energy was as low as could be detected.
What are the characteristics of an arc on the electrical circuit? I teach an apprenticeship class and I would like to be able to explain the theory to the class.
What makes the AFCI protection any different from that in a standard circuit breaker?
AFCI’s have the electronics to open the circuit for low-level line-to-neutral faults when three to eight half-cycles exceed 50A peak (within .5 second), whereas a standard circuit breaker might not open for many hundreds of half-cycles.
Why not trip the AFCI in one or two half-cycles, instead of three to eight half-cycles?
If the AFCI tripped in one half-cycle then, then many voltage surges could cause the protection device to trip and in many cases we might not be able to turn on the loads on. A light bulb sometimes takes two
Half-cycles to burn out, so two is out.
Does a GFCI circuit breaker offer equal or greater performance than an AFCI circuit breaker, given the same conditions for which an AFCI breaker was designed?
GFCI circuit breakers are designed to protect against ground faults of 6 mA or more, short-circuits, and overloads. Dual listed AFCI/GFCI circuit breakers are designed to protect against ground faults of 6 mA or more, short circuits, overloads, and arcing line-to-neutral faults. Dual listed AFCI/GFI circuit breakers are designed to protect against ground faults in excess of 30 mA, short circuits, overloads and arcing line-to-neutral faults. A GFCI does not offer protection against arcing line-to-neutral faults.
GFCI Ground-Fault Circuit Interrupter. A device intended for the protection of personnel that functions to de-energize a circuit within an established period of time when a current to ground exceeds the values established for a Class A device. Class A ground-fault circuit interrupters trip when the current to ground has a value in the range of 4 mA to 6 mA. For further information, see UL 943, Standard for Ground-Fault Circuit Interrupters. See Article 100.
GFI Ground-Fault Protection of Equipment. A system intended to protect equipment from damaging line-to-ground fault currents by disconnecting all ungrounded conductors of the faulted circuit.
Ground-fault protection is intended to protect just the equipment itself because it is sensitive to leakage currents above 30 mA. These protection devices are intended to substantially reduce the risk of a fire by a low-level electrical arc. For further information regarding ground-fault equipment protection, refer to the UL General Information for Electrical Equipment Directory (White Book), category KCZI.
Note: Ground-fault protection devices are not the same as a ground-fault circuit interrupter used for personal protection.
Additionally both UL489/943/1699 and UL489/1053/1699 devices provide grounded-neutral protection. This is very important as a high resistance glowing contact at a receptacle terminal is equally likely to occur at the neutral as the line screw terminal. The insulation failure that occurs when the neutral wire-terminal connection overheats can lead to a neutral-to-ground fault. The fault can be external to the receptacle (glowing neutral wire touching bare ground wire or grounded outlet box) or internal to the receptacle (the result of a failure of the neutral-to-ground plastic insulation barrier as the result of the plastic melting).
While both UL943 GFCI and UL1053 GFI circuit breakers protect against a grounded-neutral condition there is a difference in how they do this. A UL943 device inserts a small voltage in the neutral conductor via a transformer. When load neutral is connected to ground this transformer generates a ground fault current which can trip the GFCI, even if there is no load current. A UL1053 GFI device requires load current to produce a ground current. The difference in grounded-neutral protection is not important for glowing contact protection as load current must be present for a glowing contact to exist. I only mention this difference for completeness.
It’s important to know that today’s AFCIs include some sort of ground fault protection. One of the more common wiring faults customers encounter when installing an AFCI in a new or retrofit installation is a “shared neutral” condition (two black wires feeding circuits with a common white wire return). If the electrician does not “load test” the AFCI protected circuit before he leaves can experience a call back if a shared neutral condition exists. Two-pole AFCIs are available for this condition.
*The 2002 NEC states that all branch circuits that supply 125V, 15A or 20A outlets in dwelling unit bedrooms be AFCI protected. Would this apply to smoke detectors and wall air conditioning units connected to a 125V, 15A or 20A circuit? **
AFCI protection is required for all 125V, 15A and 20A outlets, and this would include the outlet for smoke detectors as well as wall air conditioners. Reports from the field indicate that AFCI breaker’s will nuisance trip when they supply motor loads.
Cutler Hammer Note: The UL1699 AFCI standard requires nuisance tripping testing with a capacitor-start motor drawing a minimum peak current of 120-A. We use an air compressor for this test that draws 145-A peak. An air conditioner should not experience a nuisance tripping problem.
Is AFCI protection required for switches located in the bedroom that controls a lighting outlet in another space?
If the switch controls utilization equipment in the bedroom, then it will be AFCI protected. However, if the switch operates lighting outlets for outdoor luminaire, closets or other loads not terminated in bedroom space then AFCI protection is not NEC required, because a switch is not considered an outlet.
*According to Article 100, an outlet is defined as a point on the wiring system at which current is taken to supply equipment that utilizes electric energy for electronic, electromechanical, chemical, heating, lighting, or similar purposes . This would include a receptacle outlet, a lighting outlet, but not a switch.
Lutron Note: Phase-control dimmers may cause nuisance tripping when used with Arc-Fault Circuit Interrupters (AFCIs). This nuisance tripping is dependent on the load wattage and the number of high wattage lamps on each Arc-Fault Circuit Interrupter. The use of high wattage lamps or large wattage loads will increase the chance of nuisance tripping when a dimmer turns on. This is only an issue when a dimmed circuit turns on and is not encountered during dimming or fades.
Cutler Hammer’s Comment: The UL1699 standard for 15 and 20 ampere AFCIs includes testing with 1000 watt incandescent lamp dimmers. This is appropriate for residential circuits. Staying at or below 1000 watts of total dimmed lamps per AFCI circuit should result in nuisance free performance. Additional loads can be on the circuit, just not dimmed loads.
**It seems to me that the demonstration you witnessed proved only that a GFI breakers improve safety, not that AFCI breakers improve safety. I don’t understand why you feel a dual listed AFCI/GFI breaker is any better than a GFCI breaker. **
Because a GFCI circuit breaker, by it’s self does not have line-to-neutral arc fault protection that contained in an AFCI breaker.
What still doesn’t make sense to me is that if a GFCI breaker trips at a lower level than an AFCI - why mandatory AFCI? Why not an option to use GFCI?
A GFCI protection device offers tremendous line-to-ground and neutral-to-ground protection (maximum 6 mA), but a GFCI will not clear a line-to-neutral arcing faults in three to eight half-cycles, only a AFCI can provide this level of protection.
I don’t see the value of an AFCI protection device that is not GFI or GFCI listed because it only senses a line-to-neutral fault, and really how often does that happen in branch-circuit wiring?
I agree with you, the likely hood of a line-to-neutral fault in branch-circuit wiring causing a fire is very rare. But a line-to-neutral arc could occur in two wire NM cable or knob-and-tub wiring (particularly in the outlet boxes). Line-to-neutral faults are very common inside an outlet box when the conductor insulation melts because of excessive heat from loose terminals or connections. Only an AFCI is capable of clearing the fault within three to eight half-cycles.
I can’t imagine any type of fault on a Code compliant building wiring system that will not develop into a ground fault which would be protected by a GFCI.
The likely hood of a line-to-neutral fault not evolving into a ground-fault is not likely in today’s NEC compliant wiring systems consisting of metal boxes, raceways and cables. Installations consisting of metal enclosures, raceways and cables should be safe from a fire if GFCI. But a GFCI protection device cannot be installed on all circuits because of leakage current from induction loads such as motors and fluorescent fixtures. The ground-fault setting on an AFCI is much higher than the 6 mA setting of a GFCI.
Does an AFCI/GFI provide the same level of ground fault protection as a GFCI device?
No, AFCI/GFI circuit breakers will de-energize the circuit when the ground fault exceeds 30 mA, whereas an AFCI/GFCI circuit breaker opens at 6 mA and greater. However, a AFCI/GFCI circuit breakers should only be installed on circuits where nuisance tripping would not be a problem.
There are many homes dating back to the 1920’s that still have knob-and-tube that has outlasted subsequent wiring technology, such as BX with rubber insulated conductors and early forms of romex. Do AFCI breakers protect existing knob-and-tube wiring systems?
An AFCI circuit breaker will trip and clear the circuit when a line-to-neutral arc occurs (often caused by the melting of the conductor insulation at loose terminals) within three to eight half-cycles, whereas a standard circuit breaker might not open for many hundreds of half-cycles. Note: If the AFCI is dual listed as a GFCI, the two wire receptacle can be replaced with three-wire receptacles and no equipment grounding conductor is required to be run to the receptacles [406.3(D)(3)].
I’ve heard that AFCI devices won’t protect against fires from 2-wire NM cable. Is this true?
False. AFCI’s have superior performance protection over a standard circuit breaker when it comes to low-level line-to-neutral faults. In an old house I would surely install them, even though they are not required by the NEC.
Is it okay to replace a regular circuit breaker with an AFCI circuit breaker if there are GFCI receptacles on the circuit in question?
Yes. The GFCI receptacle should not interfere with the AFCI protection circuitry.
What type of arcs are the most common factors in electrical fires, and will today’s AFCI circuit breakers detect these faults?
An AFCI is designed to detect and clear a line-to-neutral fault under conditions where a standard circuit breaker might not (3 to 8 cycles as compared to 600 half-cycles, depending on the available fault at the failure). Loose electrical terminations and connections should generate enough heat to create a line-to-neutral fault or a line-to-ground fault, which will be detected by the AFCI or GFI circuitry.
I have heard that the AFCI technology would be improving in the future. What do you think?
I don’t know if the AFCI technology in a circuit breaker can be made to do more than it does right now. You have to understand that this technology is not new. The manufacturers have been working on this for almost 10 years.
Would an AFCI circuit breaker work as a service or feeder protection device?
No, because they are limited by UL to 15A and 20A, 120V.
Are the electronics in AFCI devices subject to the damaging effects of high-voltage surges? And if so, do they continue to energize the circuit giving the false impression that they are working properly?
Yes and yes. The electronics in AFCI devices are subject to the damaging effects of high-voltage surges, just like a GFCI circuit breaker. The instructions supplied with both GFCI’s and AFCI’s stress that they should be tested monthly to ensure that they are operational.
NOTE: The AFCI UL standard was recently revised to raise the surge voltage test from 4kV/2kA to 6kV/10kA and all permanently connected AFCI’s must meet this requirement by July 15, 2004.
I read there’s a nuisance-tripping problem with AFCI devices. Has this problem been resolved yet?
The major problem is that some installers do not yet understand how the AFCI circuit protection device operates. If there is a neutral-to-ground connection on the load side of the circuit breaker, the breaker will not trip until a load has been applied, whereas a GFCI, even without load, will not operate until the neutral-to-ground connection has been removed.
What occurs is that the electrician leaves the property after installing and turning the devices on, then the homeowner calls two hours later complaining that there is no power. Trouble-shooting determines that as soon as a load is applied, the AFCI trips because of a faulty neutral-to-ground connection on the load side of the device.
**Why does the NEC only require AFCI protection for bedroom circuits? **
This is an area in the home where the disabled, elderly, and young children spend a great deal of their time. The ratio of the bedroom space to the total area is relatively large as compared to the ratio of the number of bedroom circuits to the total number of circuits. So, basically, you get the most protection for the cost.
Mike, do you think the data supports the requirement that AFCI protection devices should be required by the NEC in new homes?
No, but if the NEC does not require it when the home is built, then there is no way to require it later when it’s really needed. However, newer homes have fires via electrical origin as well, just statistically at a lower rate than older homes.
Will you be replacing the breakers in your home with AFCI breakers?
Well, that’s a tough one. They are very expensive (about $30 each) and if I replaced all of them, it would cost me about $1,500. I will have an electrical contractor visit my home and check all terminals for tightness. Since it’s a new home, I don’t feel the risk is that great.
Should the NEC expand the requirements for AFCI’s?
It’s easy for me to give opinions because I don’t have all of the facts and it won’t cost me anything. Since I have confidence in the NFPA Code process, I’ll leave this tough decision to the experts that sit on Code Panel No. 2.
What do you do about an older house with fuses? Are you required to upgrade your panel if you do any modifications within a bedroom?
AFCIs are not required for existing homes.
Do AFCI breakers work with multiwire circuits?
Yes if it’s of the two-pole AFCI type.
**I was under the opinion that when any renovation/modification is done to a bedroom, even adding an outlet, the wiring was required to be upgraded to the AFCI protection requirement. Is this the correct assumption? **
This is up to the local electrical inspector/building official.
To the best of my limited knowledge, there is still no way to test any of these breakers. How can an AHJ approve a device that may or may not be working properly?
Sure there is http://www.mikeholt.com/news/archive/html/20/AFCI_Tester_08-16-2002.htm I have one!
AFCI Questions and Answers
Bumped…Good Information !
I agree, Thanks Paul!
when upgrading a panel to 200 amp do you need to change breakers to afci also adding 1/240 volt circuit for air conditioner and1/120 circuit for outside plug gfci
For the existing circuits I would say no, for the new circuits yes if they’re in an area that requires AFCI protection.
The outside circuit is not on the list that require AFCI protection, neither are 240 volt circuits.
Good point Jim. My response seems to have nothing to do with the installation of the two new circuits.
Does anyone us the Ideal 61-165 circuit analyzer to test AFCI’s as well as voltage drops, bootleg grounds, etc.?
Would it lead to increased liability and lack of insurance coverage (for those tests). “Mission creep” is something we have to watch out for where the insurance company says “we don’t cover that”, or “you tested this, but you “failed” to test that” (fill in the blank). I have always felt “best effort” was better than get in and out as quickly as possible for a low fee.
It’s a substantial investment and I don’t know of a single inspector in the Los Angeles area who uses one. Can anyone give some feedback on the advisability of doing this type of advanced testing, beyond InterNAHCI Standards?