Are AFCI's all they're cracked to be?

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SAC

Senior Member
Location
Massachusetts
And I guess while we seem to be on the subject of questioning AFCIs - the big complaint I have is that there doesn't seem to be any required "proof" to us, the American people (or anyone else as far as I can tell), that they actually do much of anything. I may be wrong, but my understanding is that there is no standard for compliance testing that proves that any given AFCI actually "works". The algorithms used by any particular AFCI are proprietary and aren't required to be revealed to the public for scrutiny. Given no standard compliance test and no requirement for algorithm disclosure, how can anyone say the are worth much of anything to the customer?
 

MarkyMarkNC

Senior Member
Location
Raleigh NC
It will probably be another five+ years before there is enough data to show whether or not they are a genuine, high-tech life saving device, or a crock foisted upon us by greedy breaker manufacturers.
 

pfalcon

Senior Member
Location
Indiana
In case you are curious where the fuzziness in the sine wave comes from:
http://science.howstuffworks.com/nature/natural-disasters/lightning4.htm
Same principles are at work. The power is distorted prior to the "arc" in trying to generate the plasma bridge. That bridge requires power.

An expensive AFCI will attempt to identify the power fluxes associated with building the bridge. And then only trip when that signature appears. The pattern is predictable but takes a level of sophistication to detect in real time.

A cheap AFCI will model a normal sine wave and trip when the signature is outside tolerance for a normal wave. Much easier to detect but much more prone to false positives.
 

Mr 3phase

Member
Last summer, I wired a finished attic to be used as a bedroom, and installed one new circuit (small room area), and used an arc fault breaker as required. 5 months later I am getting called back because the breaker keeps tripping. I unplug everything, shut off the lights, reset the breaker. Start by turning on the lights, no problem. Start plugging in items, such as clock radio, t.v., vcr., breaker trips. After an hour of trying different things I find that the VCR was tripping the breaker! I even replaced the breaker with a new arcfault breaker. The VCR was the culprit.
 
Read the linked post. This is their explanation:

>>>How does arc fault detection work? In essence, the detection is accomplished by the USE OF ADVANCED ELECTRONIC TECHNOLOGY to monitor the circuit for the presence of ?normal? and ?dangerous? arcing conditions.<<<

I'm sorry, but that explanation is like "this is how black magic works, by using the ethereal forces around us, we channel the....
How exactly they monitor "normal arcing" from "abnormal arcing"?

>>>Unlike a standard circuit breaker detecting overloads and short circuits, an AFCI utilizes advanced electronic technology to ?sense? the different arcing conditions. While there are different technologies employed to measure arcs by the various AFCI manufacturers, the end result is the same, detecting parallel arcs (line to line, line to neutral and line to ground) and/or series arcs (arcing in series with one of the conductors).
<<<
HOW?
It works like ANY computer program; based on math.
You observe all different types of 'normal arcs' such as occur during switching of a slew of equipment. Then you do the same with all types of different 'abnormal arcs' and record the data. Then you build a mathematical model based on the observation and then it is a go/no-go situation. The main factors in your model will be current and time. There is already a slew of data available from LV and MV relay software building as arcing faults have been addressed there for a long time - if we can talk about length in the timeline of digital relay development at all. So as the cost of microprocessors becomes less and less you see 'smartness' migrating down to lower and lower levels.
Do NOT expect that somebody will fully explain HOW any particular device works. The math formula is a closely guarded secret, because that is how everybody stays competitve. Often times even the publicly released details will lack key elements or even outright misleading.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
It works like ANY computer program; based on math.

Do NOT expect that somebody will fully explain HOW any particular device works. The math formula is a closely guarded secret, because that is how everybody stays competitive. Often times even the publicly released details will lack key elements or even outright misleading.
That's a good way to say it.

The link to the AFCI Arc Discrimination White Paper for the IEEE shows some of the ideas in the mathematical representation of the signal an AFCI "sees".

At any given instant, the information in the analog voltage and current of the branch circuit passing through an AFCI is manipulated multiple ways, simultaneously. That is, the analog "signal" on the branch circuit is sent through several different processors. The output of each processor is a number that can be positive or negative. The number output of each processor is sent to an accumulating register and added to whatever number is already there. When the accumulating register total exceeds a certain amount, the breaker trigger process commences.

The analog signal on the branch circuit conductor is turned into several numbers that are, in turn, mathematically manipulated again.

This is a "logic structure" that will change a lot as the R&D teams ripen the design of a model of an AFCI.

I suggest that we are seeing the emergence of the third generation of AFCI as the GE Mod 3 has arrived with the ability of a single pole breaker to protect one side of a multiwire branch circuit with or without the MWBC neutral connected to the AFCI. This means there is no ground fault sensing component in the normal sense of a class A GFCI. Rather, even the ground fault sensing has been abstracted into the mathematical signal processing.
 
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ELA

Senior Member
I suggest that we are seeing the emergence of the third generation of AFCI as the GE Mod 3 has arrived with the ability of a single pole breaker to protect one side of a multiwire branch circuit with or without the MWBC neutral connected to the AFCI. This means there is no ground fault sensing component in the normal sense of a class A GFCI.

Rather, even the ground fault sensing has been abstracted into the mathematical signal processing.
Al,
Curious if I your last line is something you have read or are speculating on?
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
Al,
Curious if I your last line is something you have read or are speculating on?
I probably could've stated that a little better.

As I understand it, there is no actual requirement in the AFCI standards for ground fault detection, but it has been incorporated by manufacturers in all AFCIs prior to the GE Mod 3 in order the get a behavior that will pass the UL tests.

The GE Mod 3 claims to have no ground fault detection component, so, to me, this says the mathematical modeling of the arc discrimination has improved, or expanded, to include those fault conditions only addressed in the past by ground fault detection.

I wasn't trying to say that a digital (or mathematical) GFCI had been created.
 

readydave8

re member
Location
Clarkesville, Georgia
Occupation
electrician
I still don't like paying $35 for a single pole 20 amp snapin breaker.

And the rewiring I'm doing on an existing house needs 10 AFCI's.

And its a QO, so the breakers are $57 each.
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
I am so PO right now I could just puke. Set some walls in my basement today and need to anchor the bottom 2by. Got me a brand new hammer drill. Virgin. Works well until you put a bit of pressure on it. Trips the AFCI. Been using the same gfci recept for a chop saw and an old vacum for two days.

Are AFCIs all they're cracked up to be?


NO!!!!!
 

ELA

Senior Member
I probably could've stated that a little better.

As I understand it, there is no actual requirement in the AFCI standards for ground fault detection, but it has been incorporated by manufacturers in all AFCIs prior to the GE Mod 3 in order the get a behavior that will pass the UL tests.
What part of the UL tests did the ground fault detection help the breaker to pass?


The GE Mod 3 claims to have no ground fault detection component, so, to me, this says the mathematical modeling of the arc discrimination has improved, or expanded, to include those fault conditions only addressed in the past by ground fault detection.

I wasn't trying to say that a digital (or mathematical) GFCI had been created.
Thanks for the clarification.
I had always wondered if the GF section of the AFCI breakers was more of a CYA just in case the arc detection did not work.
Now I wonder if it just became to difficult to make both the AFCI function and GF both work properly together on these new - MWBC compatible devices?
 

kwired

Electron manager
Location
NE Nebraska
My understanding is that basically what is done is to create a lot of arc fault conditions in the lab, and look at what the electrical waveform looks like at the breaker. This is done for all kinds of different cases (but obviously not all of them). Then they look at all kinds of "normal" loads, such as CFLs, refrigerators, vacuum cleaners, hair dryers, etc., to see what the electrical waveform looks like at the breaker. Then they write software that tries to analyze the electrical waveform at a breaker and detect when there is one that looks like what an arc fault creates, but not one that looks like what a "normal" load creates. If one is found that looks like an arc fault, and not "normal", the software trips the breaker.

This is a problem that is very similar to that in other fields, such as monitoring heart beats for irregularities. However, this may be one of the most difficult scenarios given the space and cost restrictions (compare the cost and size of a breaker vs. a heart monitor), and well as the similarity of the arc fault "fingerprint" to many "normal" ones. I'm not an expert, but from what I've read I'm not convinced (as apparently the decision makers have been) that they have gotten the recipe right yet. Though as time goes on and the processing power that can be put into a breaker at a given cost increases, I'd expect things to get better (as well as appliance manufactures having to design them so that they won't trip the arc faults).
So why not develop a programming module and be able to program these devices to recognize an acceptable load? At least those of us who service them will be able to look like we know what we are doing with these things. Many of us run into a problem load that the device does not like and end up telling the customer that there is nothing we can do about it. That is not good for the reputation of the installer or the equipment, but makes the handiman that solves the problem by putting in a standard breaker look like a genius to the homeowner.

I don't know how the people pushing the use of these (which I think is good, but they definately are still in infancy) ever expect them to discriminate between all possible loads that could be placed on them and known problem load conditions.

I see no reason why any manufacturer should have to redesign their equipment so that the AFCIs will work correctly. It is my opinion the issue is up to the AFCI manufacturers to solve.
My opinion also. I think they also should have been perfected more before being put into code, instead all that was important was the fact that several manufacturers needed to have one before forcing us to use them.

.. Two choices - fight the government and try to get AFCIs removed from the code, or try and change the vacuum so it doesn't trip AFCIs .
Where does the government come into play in requiring AFCI's other than in cases where government operated AHJ's adopt and enforce the NEC as it is printed? They do not make the NEC, sometimes they do amend it for whatever reason they feel is necessary. I can give you one example of government eliminating AFCI requirements:

Nebraska State Electrical Board amended out all AFCI requirements in past codes because (not an official statement but my understanding) they felt that the AFCI's were pushed into the code before they were ready for consumers to use them. The manufacturers had a lot invested in R&D and did not want to wait another code cycle or two to further perfect the product so they pushed hard to get it in code and made the consumer be the testing lab. I think Nebraska was one of very few places that completely amended all AFCI requirements to non existance in their code.

In 2008 Nebraska Electrical Division decided they wanted to adopt 2008 NEC without AFCI amendments - (maybe, I don't know all facts of why) they decided the first generation AFCI's were being replaced with supposably an improved product and now maybe we should allow them.

Problem is every three years when the new NEC gets adopted, because it will become state law, has to be passed by the state legislature. Normally this happens with little or no debate, law is introduced and passed

But the 2008 NEC and no more amendments deleting the AFCI requirements, plus the tamper resistant receptacle requirements, weather resistant receptacle requirements, had some homebuilder associations presenting some strong opposition so it got tabled and was not brought up again before legislative session was over for the year.

Same thing pretty much happened in 2009. Eventually 2008 code was adopted in middle of 2010. I'm not sure of issues involved that got it passed. I don't know if 2011 code is expected to have any similar issues or not. I'm sure a bill will be introduced to adopt 2011 and likely will not even come to the floor until maybe March, if passed will still be 90 days before it is a law unless there is an emergency clause - I doubt that is even slightly possible with that particular bill. The state budget will be getting the most attention in this years session.
 

kwired

Electron manager
Location
NE Nebraska
What part of the UL tests did the ground fault detection help the breaker to pass?




Thanks for the clarification.
I had always wondered if the GF section of the AFCI breakers was more of a CYA just in case the arc detection did not work.
Now I wonder if it just became to difficult to make both the AFCI function and GF both work properly together on these new - MWBC compatible devices?
I don't have any real clue as to why they have a GF section to them but it does kind of make sense to me to have them trip if there is a fault to ground no matter what the current signature is, this would typically be undesired current no matter what the source of it is or how low the current is.

Then there is (2008 code) basically any 210.52 required outlet that is not required to be GFCI protected, must be AFCI protected (as well as the entire branch circuit with the AFCI). There are some exceptions but you can almost say if it is not required to be GFCI protected it must be AFCI protected. Kind of makes you wonder how big of a player the GFCI function is in the AFCI.
 

SAC

Senior Member
Location
Massachusetts
Where does the government come into play in requiring AFCI's other than in cases where government operated AHJ's adopt and enforce the NEC as it is printed?
Well, where I live it is called "The Massachusetts Electrical Code (527 Code of Massachusetts Regulations 12.00)" - I call that "government"! I certainly don't get to make the choice for myself - when the electrician shows up I don't get asked "want the plain ol' breaker or the fancy AFCI"? "Something" already made the decision for me... :)
 

kwired

Electron manager
Location
NE Nebraska
Well, where I live it is called "The Massachusetts Electrical Code (527 Code of Massachusetts Regulations 12.00)" - I call that "government"! I certainly don't get to make the choice for myself - when the electrician shows up I don't get asked "want the plain ol' breaker or the fancy AFCI"? "Something" already made the decision for me... :)
And did the government write this code themselves with their own process of making the requirements, or is it actually an adoption of an existing standard with or without some amendments as they see fit?

And if it is truly a government written law and not an adoption of a well known standard, apparently the majority accept it otherwise it likely will be getting changed.
 
I agree. They should make their product compatible with existing equipment.
No argument there, BUT.

It is akin to trying to make something idiot proof. You make the product then a better idiot shows up.:D

There are literally hundreds of new product shows up on the market every day. Even if a manufacturer test every product that is available at the time of the product design, by the time they get the approval from the listing agency after months of testing, there will be thousands of 'untested' products on the market.

The way around it? Write into the PRODUCT testing standard the parameter limitations for arcing fault protection. There will be of course a bevy of old products and products that do not get tested, just slapped on nice holographic UL labels available on e-bay at $10.00 per hundred. http://cgi.ebay.com/500-CUSTOM-PRIN...986?pt=LH_DefaultDomain_0&hash=item45f5b8fdfa
 

Strife

Senior Member
Thank you all for the reply.
I learned a few things from the reply.
I haven't thought about the wave form being used to detect arc faults. Definitely a viable formula.
But I also learned that (under the disguise of "proprietary information") no one can really tell if AFCI's really work, or are just glorified GFCI's.
Which is sad considering we must have spent a few billions on a product that's just as proven as palm reading.
 
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