AFCI
- Thread starter Mattste
- Start date
- Status
bdarnell
Senior Member
- Location
- Indianapolis, IN
- Occupation
- Retired Engineer
Re: AFCI
According to the code making folks here in Indiana, they don't.
According to the code making folks here in Indiana, they don't.
- Location
- Massachusetts
Re: AFCI
Do we know that they do?
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: AFCI
The "simple answer," and the only answer I know, is that the AFCI breaker contains an electronic sensor that looks at the waveform of the current as it passes through. The electronics are designed to look for a pattern, an "electronic signature," that is typical of an arcing fault. If it sees that signature, it trips.
The "simple answer," and the only answer I know, is that the AFCI breaker contains an electronic sensor that looks at the waveform of the current as it passes through. The electronics are designed to look for a pattern, an "electronic signature," that is typical of an arcing fault. If it sees that signature, it trips.
Re: AFCI
To elaborate on Charlie's explanation:
AFCIs have a tiny occiloscope in them. Forcus on the screen is a tiny TV camera which sends its signals to a small computer chip which translates the video signals into digital. These are analyzed, catalogued and compared.
Meanwhile, according to Mike Holt's newsletter pf Monday, Dec.9, 1902, the receptacle heats up until it glows red hot and melts. Eventually a ground fault develops between the hot wire and ground creating a ground fault. Inside each AFCI is also a ground fault detector that senses this and trips. A regular breaker does not have this ground fault detecting capability and will not trip. Therefore the AFCI is superior.
~Peter
To elaborate on Charlie's explanation:
AFCIs have a tiny occiloscope in them. Forcus on the screen is a tiny TV camera which sends its signals to a small computer chip which translates the video signals into digital. These are analyzed, catalogued and compared.
Meanwhile, according to Mike Holt's newsletter pf Monday, Dec.9, 1902, the receptacle heats up until it glows red hot and melts. Eventually a ground fault develops between the hot wire and ground creating a ground fault. Inside each AFCI is also a ground fault detector that senses this and trips. A regular breaker does not have this ground fault detecting capability and will not trip. Therefore the AFCI is superior.
~Peter
Re: AFCI
My guess:
If an arc occurs, the current is not sinusoidal. The arc will extinquish itself 120 times per second and restrike 120 times per second. This leaves a dead zone around the normal zero crossing. This pattern is somehow sensed and analyzed. I would guess that DSP, Digital Signal Processing, technology is used.
It is my understanding that AFCIs detect series arcing as well as shunt arcing. This would be quite valuable with aluminum wire and/or backstabbed receptacles.
My guess:
If an arc occurs, the current is not sinusoidal. The arc will extinquish itself 120 times per second and restrike 120 times per second. This leaves a dead zone around the normal zero crossing. This pattern is somehow sensed and analyzed. I would guess that DSP, Digital Signal Processing, technology is used.
It is my understanding that AFCIs detect series arcing as well as shunt arcing. This would be quite valuable with aluminum wire and/or backstabbed receptacles.
Re: AFCI
A GFCI is designed to detect faults between a neutral and ground or hot and ground,but not between hot and neutral. That is the idea behind the AFCI. They both protect from respective faults inside the wall as well as cord connected equipment. AFCI basically designed to eliminate fires caused by two wire lamp cords that get frayed behind the bed when it gets to rocking. It also is supposed to provide some sort of protection for other equipment that does not have a ground to facilitate the tripping of a normal breaker. I suppose smoke detectors would be included in that.
A GFCI is designed to detect faults between a neutral and ground or hot and ground,but not between hot and neutral. That is the idea behind the AFCI. They both protect from respective faults inside the wall as well as cord connected equipment. AFCI basically designed to eliminate fires caused by two wire lamp cords that get frayed behind the bed when it gets to rocking. It also is supposed to provide some sort of protection for other equipment that does not have a ground to facilitate the tripping of a normal breaker. I suppose smoke detectors would be included in that.
- Location
- Massachusetts
Re: AFCI
That said I am not sure I understand your question.
If any of the smokes are located in a bedroom and you are under the NEC 2002 or 2005 without amendments you will have to put the smokes on a AFCI.
As to what good it will it do?
It will meet code, after that no one really knows if the AFCI will function.
I also do not understand why you say the smokes are not grounded.
The branch circuit has a ground right?
[ January 07, 2006, 06:47 AM: Message edited by: iwire ]
You probably should have started a new topic for your question.
That said I am not sure I understand your question.
If any of the smokes are located in a bedroom and you are under the NEC 2002 or 2005 without amendments you will have to put the smokes on a AFCI.
As to what good it will it do?
It will meet code, after that no one really knows if the AFCI will function.
I also do not understand why you say the smokes are not grounded.
The branch circuit has a ground right?
[ January 07, 2006, 06:47 AM: Message edited by: iwire ]
- Location
- Windsor, CO NEC: 2023
- Occupation
- Hospital Master Electrician
Re: AFCI
Smoke detectors, having no exposed metal parts, have no grounding conductor on the unit itself.
This has no effect on the AFCI, it will "function" without grounding conductors to equipment.
Check out Mike Holt's article on AFCI's and this article from Square D dudes.
Smoke detectors, having no exposed metal parts, have no grounding conductor on the unit itself.
This has no effect on the AFCI, it will "function" without grounding conductors to equipment.
Not really. It's not designed to look for normal "faults" at all, but to sense if any point on the branch circuit is arcing. So if a AFCI circuit breaker senses a arcing pattern in the current flow that it has been programmed to react to, it will trip.
That may be what the original sales pitch was to the NFPA, but that does not describe the capabilities of the branch/feeder AFCI we use today. The change in the 2005 code asking for "combination" AFCI's is the NFPA asking for the product they originally thought they were getting.
That is not correct. 406.3(D) allows GFI protection of existing circuits lacking an EGC, but an AFCI breaker is not the same thing.
Check out Mike Holt's article on AFCI's and this article from Square D dudes.
Re: AFCI
Let's get this straight:
A POCB (Plain Old Circuit Breaker) trips on excessive current--fault or overload.
A GFCI trips on small imbalances between hot and neutral currents such as might be seen with a few milliamps thorugh one's bod from hot to ground.
An AFCI trips on arcing which might occur with loose connections, worn insulation, or carbonized plastic.
I believe breakers are available which perform all these functions--for a price.
Let's get this straight:
A POCB (Plain Old Circuit Breaker) trips on excessive current--fault or overload.
A GFCI trips on small imbalances between hot and neutral currents such as might be seen with a few milliamps thorugh one's bod from hot to ground.
An AFCI trips on arcing which might occur with loose connections, worn insulation, or carbonized plastic.
I believe breakers are available which perform all these functions--for a price.
- Location
- Illinois
- Occupation
- retired electrician
Re: AFCI
1) the series arc progresses into a parallel arcing fault and the AFCI detection circuit opens the circuit,
2) the series arc progresses into a line to ground fault and the GFP part of the AFCI breaker opens the circuit, or
3) the series arc progresses into a neutral to ground fault and the GFP part opens the circuit.
The real question is whether one of the above happens before the fire starts.
Don
Not exactly. The AFCI does not driectly act on arcing that would be caused by a loose connection or a single broken wire. That would be a series arc and the arc detection chip in an AFCI does not detect series arcing. The AFCI, may, after a period of time, respond indirectly to the series arc or high resistance fault. It does this only when one or more of the following occur.
1) the series arc progresses into a parallel arcing fault and the AFCI detection circuit opens the circuit,
2) the series arc progresses into a line to ground fault and the GFP part of the AFCI breaker opens the circuit, or
3) the series arc progresses into a neutral to ground fault and the GFP part opens the circuit.
The real question is whether one of the above happens before the fire starts.
Don
- Location
- Windsor, CO NEC: 2023
- Occupation
- Hospital Master Electrician
Re: AFCI
Actually, according to Mike Holt's article (linked in my previous post) even the new combination types would not likely trip due to loose connections.
- Location
- Illinois
- Occupation
- retired electrician
Re: AFCI
rattus,
Don
rattus,
Not likely...all switching devices produce series arcing.
Don
Re: AFCI
Don
I have gone on jobs to hang a fan and without knowing how tripped the afci. I always assumed it picked up a ground to neutral when I was handling the wires. However today I tried to trip a GE gfci with the switch off I touched the ground and neutral, sw. leg to neutral and sw. leg to ground nothing seemed to trip it. Then I created a series arc and again could not trip it.
If I remember the ones I have seen trip were CH brand.
Just when you think you got this figured out it changes.
Don
I have gone on jobs to hang a fan and without knowing how tripped the afci. I always assumed it picked up a ground to neutral when I was handling the wires. However today I tried to trip a GE gfci with the switch off I touched the ground and neutral, sw. leg to neutral and sw. leg to ground nothing seemed to trip it. Then I created a series arc and again could not trip it.
If I remember the ones I have seen trip were CH brand.
Just when you think you got this figured out it changes.
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