OK, if you haven't yet read this IEEE paper, do so now, before proceeding:
http://www.combinationafci.com/resources/doc_ieee_combination_afci.pdf

Now, for the point of this thread:

The author refers to a 'law of physics' which, he asserts, proves that a series arc cannot form between copper electrodes (think: broken wire) at household voltages.
(See page 7 of the paper)

The graph included in the paper as "Figure 5" does not support this. It is a graph of voltage vs. air pressure, with the electrodes kept 1" apart at all times. He posted the wrong graph.

I am looking for links, or other DATA, that directly address his assertion.

Any takers?

http://en.wikipedia.org/wiki/Paschen%27s_law

http://home.earthlink.net/~jimlux/hv/paschen.htm

http://www.highvoltageconnection.com/articles/paschen-curve.html

(I don't know why it is highlighting one link and not the other two)

This would apply for a sustained gap, where no re-contact between conductors would happen to re-draw the arc. And in reality, we can see these series arcs happen with very very narrow (smaller than a millimeter) gap. In addition to the air gap breakdown voltage, there is a voltage drop characteristic, much like seen in semiconductors, whenever you have transitions between different metals and the arc. I have only found a small amount of science on these aspects of arcs. But they do play some role in gas-discharge lighting.

"Using Paschen's Law, the minimum breakdown in air is calculated to be 327 V at standard atmospheric pressure. This occurs at a distance of 7.5 µm."

That's the statement we need to explore.

As I read it, that statement claims that you cannot have a sustained arc at household voltages- and the voltages are even higher for larger gaps. 7.5 microns is a very small gap. Microscopic, even.

Yet, we've all encountered 'damage from arcing' at contactor points and panel busses.

Can anyone find a 'voltage vs. gap distance' curve?

Arc damage is cumulative and it tends to be self perpetuating. Arcs damage points and damaged points arc more.
Once you have a high resistance contact it will just get hotter, making the resistance higher, rinse, repeat.

Greg .... are you saying the damage we see is from a momentary spark? As opposed to a sustained arc?

Are we to believe that 240v. can 'spark' but not 'arc?'

A spark is an arc unless you are really splitting hairs. I agree with the author who says it is hard to maintain an arc at normal household voltages and currents but I have a buzz box welder that can maintain an arc at some pretty low voltages.

Greg:
Would I be correct that you have to start the weld by contact? And if you loose the arc, you have to make contact to restrike the arc?

How low can you drop the voltage to?

Yup ... anyone who has welded knows you can do an awful lot with 1500 watts .... even at a modest 12v setting. That's car battery voltages.

FWIW, I've drawn some pretty good arch simply by jump-starting cars. Available energy? Well, enough to detonate one such cars' battery. Yet ... could the arc have been maintained for any length of time? I have not tried it.

"Peer review" is what we're doing here. We are checking the assumptions, assertions, and logic of Mr. Engle. That means finding his sources.

Mr. Engle also makes statements in his paper that infer the composition of the electrodes matters. For a broken wire, that's a pair of copper electrodes. He asserts that there is a difference between and arc and a spark. He asserts there is a not enough energy to light cotton. He asserts that there is a difference between a 'series' arc and a 'parallel' arc.

Yet, the biggest assertion is that the laws of physics precludes arc creation. He refers us to Pashchen's Law. Well .... does the law really say that?

I would say that this matter must be resolved before the AFCI debate can proceed.

In the real world the arc path is facilitated by dust/ particulates, etc.

So Pashchen's assumptions are NOT valid.

Anyone who has dine much welding know striking and maintaining the arc is the tricky part until you get a feel for it but bad luck seems to have a way of accomplishing hard things.
I imagine the real reason natural AC arcs self extinguish so fast is that they can't advance the electrode at the speed it is being burned away.
When we want to put the fire out on an AC contact, we will bridge that gap with a resistor/capacitor network. I understand that makes the "zero crossing" a little longer by slowing down the rise, giving the arc a chance to go out.
I know the voltages involved are far beyond the circuit voltage if you have an inductive load.

For ease of the readership, here is what Dr Engle published in his paper (i can't seem to post the graph, sorry)

~S~


Test 12: Operation Inhibit Apparently UL determined that the arc detection schemes of both Products 1 and 2 utilized the high frequency content of the current waveform.

A continuous low current series arc was created using the “arc simulators”. These simulators use
two opposing electrodes, like those of a carbon arc lamp.


Rather than use two carbon electrodes, Simulator 1 used one carbon (graphite) electrode and one phosphor-bronze electrode.

Simulator 2 used one carbon and one copper
electrode. Both simulators created a continuous low current arcing condition. The current, after each zero crossing, is zero for a few milliseconds until an arc re-strike occurs.

This re-strike transient produces a high frequency “noise” component in the arcing current waveshape.

UL evidently theorized that Products 1 and 2 series arc detection algorithms could be masked by normal continuous series arcing, such as from the brushes of an electric drill.

Also a normal EMI filter used in power strips etc. could filter the high frequency current component, so the AFCI circuit breaker would not see the arcing event.

UL was correct in their assumptions. Products 1 and 2 were tested and failed both masking tests that indicate their technology was based on looking for high frequency noise.


Why didn’t UL use copper-copper electrodes, instead of
the odd combinations of carbon and phosphor-bronze and
carbon-copper?

Unfortunately UL didn’t address this important question, and thus the validity of the use of these “arc-simulators” is questionable.

Further the author believes that UL, by
introducing their use, inadvertently gave credibility to AFCI manufacturers’ claim that their product will respond to a series arcing event.

The use of strange materials like phosphor-bronze and carbon, conductive materials not used in house wiring, might be explained but not justified, as follows:

 Copper-Copper: This combination and copper-steel are the only valid electrode choices. If UL wanted to demonstrate “real world” series arc detection they could have used copper.

UL may have tried copper but found they only got
sparks, not the continuous low current arcing that Products 1 and 2 probably needed to trip.

The reason for a simple spark is explained by a century old law of physics. A person named F. Pashchen in 1889 published a law which sets out what has become known as Paschen's Law.

He determined the relationship between breakdown voltage, the gap between two metal plates, and the pressure.


With air as the gas, the minimum voltage is 327V, as shown in Fig. 5. The peak of a 120VAC sine wave is only 170V, and thus continuous low current arcing is, by a law of physics, not possible with copper-copper.


Thus claims that a Combination AFCI will respond to arcing at a break in a
conductor or a loose connection flies in the face of a law of physics.


Fig. 5 Paschen's Law


Copper and Phosphor-bronze and Carbon-
Copper: UL did not justify the use of such strange electrode pairs.

Practically, the use of carbon made it easy to produce
continuous low current series arcing to test the claims of Product 1 and 2.

Paschen's Law applies only to metal-to-
metal arcing. Unfortunately, it also would seem to invalidate the use of any test results as part of a home electrical fire study.

I agree the choice of electrodes is questionable. If they are really testing this device they should use zip cord conductors where the fine strands have a better chance of rising to the ignition temperature of the dust bunnies under the bed (the original justification for these things).

I do not have a dog in this fight, I am just playing the devil's advocate in the arguments.

Use of carbon arc rods for arc testing. Back in the late '80s, I used to operate carbon arc spotlights for a theater. The cabon rods were plated with copper and when they operated they cast a greenish colored light. The presence of the green light indicates to me that copper was vaporizing in the arc.

True, this was not a 100% copper electrode, but does this rule out that the electrodes the UL used were wrong?

The phosphor bronze / carbon & copper(?) combination sounds alot like the same materials used in the push and pray connections on the back of cheap switches and outlets.

The addition of carbon MIGHT be justified by assuming the presence of carbon from previous arcing events.

Larry the troublemaker.

Larry, the composition of the electrodes is what I thought of as the 'next step' in our peer review of the article.

After all, if his claim regarding the 'laws of physics' is incorrect, the rest of the paper is seriously weakened.

If he's correct - that it's just not possible for a sustained arc to form between copper electrodes at household voltages - then no manner of AFCI is possible.

Dissecting the test method only counts if the theory itself is sound.

OK ... let's see if this link works:

http://printfu.org/read/electrical-...Ll2ubbyuOhrrG5mKihlLm0w7jTrbi0oNnS2oiw6g

It should take you to a paper called "Electrical Breakdown Limits for MEMS," at a site called Printfu . "MEMS" stands for 'Micro Electro-Mechanical Systems." The paper seems to be part of an electrical engineering course. Engineers: Were you sleeping through this class?

The paper opens with the graph that Mr. Engle SHOULD have had in his article.

It seems that "Paschen's Law" is at the root of some of the problems in developing micro-technology. Simply put, there aren't enough ait molecules to let an arc form at distances much less than a human hair's thickness.

OK ... so the reference to Paschen's law was relevant, and correct. Where does that leave us?

It seems to leave us with the strange situation that a sustained electrical arc - as opposed to the occasional spark - cannot cannot form between two ROUNDED COPPER electrodes in ordinary air at household voltages. We can discount the high impulse voltage that is created when the circuit opens since this is not a sustained voltage. Sparks, yes; arc, no.

For an arc to form, something else must happen. Jagged contacts. Materials other than just plain copper. An atmosphere besides air.

Oddly enough, this conforms to a sample I had, where a nicked wire was able to very neatly arc-cut through EMT for a length of about 1/8".

That still leaves us with any 'arc detecting' device being dependent on something else also happening. Sounds pretty iffy to me.

So, I'll grant Mr. Engle his point. Arc detection is pretty much a solution in search of a problem.

NEC Panels: Time to dump the AFCI. Period. Completely. It's pure snake oil. Absence of any actual arc testing in the UL standard ought to make that plain. (Perhaps that's why the standard is priced at approximately it's weight in gold).

Where do we go from here? Well, now it's the 'glowing contact.' I'm not so sure about Mr. Engle's opinions there, and that's a topic for another thread.

While Dr Engle could have expanded on Pashen's law, vaious atmospheres & metals, etc, the fundamental concept of a 'sustained arc' vs. a 'spark'remains available.



http://en.wikipedia.org/wiki/Spark_gap

A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the voltage difference between the conductors exceeds the gap's breakdown voltage, a spark forms, ionizing the gas and drastically reducing its electrical resistance. An electric current then flows until the path of ionized gas is broken or the current reduces below a minimum value called the 'holding current'. This usually happens when the voltage drops, but in some cases occurs when the heated gas rises, stretching out and then breaking the filament of ionized gas


We're all familiar with Jacob's ladder, note the volage values>>

http://www.repairfaq.org/sam/jacobs.htm#jlhdj


Perhaps even more everyday is our trade being in the presence of a 'spark' , i.e.- old switches , small to large disconnects

i would venture commutator motors provide a series of sparks, instead of a sustianed arc , even though we all can note the nusiance trips from them

in any version of Pashchen's law , we do not see a sustained arc event @ nominal household voltages


part of the problem Dr Engle laments is the definitional difference bettwen these phenomenon >>


The proposed changes to UL 1699 should have been
acceptable to all STP members. It involved no core changes;

it simply attempted to bring the Standard’s language in line with other UL standards. In particular, while the term “arcing” is defined in UL 1699, the UL terms “series arcing” and “parallel
arcing” are not defined.

Yet the manufacturers and UL on their
web sites claim that the mandated Combination, unlike the Branch/feeder, provides “series arcing” protection of cords.





Further, if UL had not taken it upon themselves to create a standard, instead of testing something to a standard, we wouldn't be discussing this issue at all>>>>




As will be explained in the section discussing UL1699, the fire curve later became the UL1699 40.4 Carbonized path arc clearing time test. This test is the only arc performance test difference between the Branch/feeder and the Combination
AFCI.
After accepting the test, the Task Force admitted its failure to develop a Standard, and turned the task over to UL.
This is not a normal UL responsibility; manufacturers develop Standards, and UL is paid to test and list products to these Standards.






The unfortunate result being>>>>




“Carbonized path arc clearing time test”
This test was discussed earlier, it makes no sense. It was thought that if the technical issues were honestly presented and discussed at this STP meeting, the test would be removed from UL 1699.

Once removed, the Branch/feeder and Combination requirements would be the same (see Fig. 16),
so there would be only a Branch/feeder AFCI. The mandate of NEC 2005 would be moot, as there would be no Combination AFCI.

The author was permitted to speak to the group for about half an hour.

The test was carefully described including the
important fact that it represented nothing more than a carefully prepared parallel fault in a VERY long extension cord.

Available short-circuit fault currents as low as 5A were used, even though UL had earlier determined that the lowest available current in a home was 75A (see Fig. 2).
It was not a series arcing fault and had nothing to do with home electrical safety.

The vote was along “party lines”. NEMA manufacturers, with a few exceptions, and UL voted against removing test.

This block of votes exceeded the 1/3 required to defeat theproposal, so it failed. The “Carbonized path arc clearing time test” would remain in UL 1699.


~S~

I think the whole AFCI thing is snake oil but if it is really a valid fix for something, we should establish what it fixes and demonstrate that this technology does the job.
The step that they all skipped was creating a real world arc that starts a real fire. Then detect that.
They have created a straw man and knocked it down.

Greg

my opinion is that if a bluecollar redneck such as i can be educated to the specific physics involved here, we all can

it's just a metter of perseverance and diligence amonst those who truly care about the trade

~S~

After review of most (not all) of the information within the two threads regarding AFCI, I made a choice on the further use of the video info I use in my classes.

Within the NEC classes, until the powers that be remove the combo designated requirements, I have to reference the Code requirements. However, I will add, as my commentary, that this technology may be flawed, and reference back to some of the subject matter in this thread.

Within my Basic class, some of the subject matter that has been included within this thread will be offered, along with the fact that this is still a NEC requirement.

That said, as AHJ, I have no recourse at the present time but to require these devices.

I have witnessed a Series Arc bridge a gap, which grew up to an Inch or more - in a very hot environment, with minimally conductive surrounding Air, and a potential of 230 VAC (measured after the event).

The bottom Element of an Electric Oven failed while in use, resulting in a Series Arc between the severed ends of the once continuous Heating Element.

When the Element failed, the established Arc could be faintly heard. My Mother and I were standing near the Oven at the time, and did not think too much about the sound - as it was similar to "Bubbling".
After about 15 - 20 Seconds, the sound became less "Bubble-Like" and more "Flame-Like", and the Oven Door was opened.
So Mom opened the Oven Door, only to be presented with a Fat Arc at the bottom Element (scared the heck out of her!!!).

Like the clown I am, I watched the Arc for a few seconds before turning off the Oven (via the Temperature knob).
That was impressive!!! Never thought such a large Plasma would be sustained across a Resistance Element, at a Potential of 230 VAC!

Element was (AFAIK) 4500 Watts, so there would have been at least 19.57 Amps flowing through the Element at the time of failure.

Arc was across the Element only. No L-G Arcing was evident.

-- Scott

As an EC i have no choice but to install what may be up to 30 afci's in a 40 circuit new house wire job here

this amounts to asking for an additional $1K

for a device(s) that provide nothing more than false security

that doesn't make me feel too good

what we can do is simply get the word out to the powers that be

if they care about our trade, they'll investigate this issue, and hopefully come to an amicable conclusion

~S~

One concern I do have with such a widespread requirement for AFCI is building up so much heat in the panel, due to packing so many continuously operating (heat emitting) devices in a confined space. Are we going to be seeing 84 slot panel used for 42 circuits?

And what is the long term reliability of AFCI? We haven't seen them in long term (and in all that heat), yet.

I think I would rather see AFCI outlet devices, since at least for residences, cords for utilization equipment may be the greatest risk (not that a nail driven into an NM isn't a risk).

I asked this question a few times and I was always assured it wasn't a problem but not really convinced.
Another thing to chew on is the 40c rating on circuit breakers. In a sunshine state garage (where panels seem to be located these days) 40c is not that far from ambient air and inside the panel it could get quite a bit higher.
That will change the trip curve.

I also agree the electronics in these breakers will not like the heat.

It would be interesting to put a temperature probe inside a panel, button it up and compare it to ambient air a few feet away. One of those little indoor/outdoor thermometers would work well for this. Maybe try the probe in different spots in the panel.

I use one of these thermometers when I am designing computer cases. They are pretty handy to see what is going on inside a closed box. Some of the nicer ones will also log high temp.

John, that's another thing that deserves considerable discussion, it's own thread, and crosses many forum boundaries.

I won't deny that we need to know the code. However ...

Each of us has a duty to know far more than the code ... we need to know how things work. How else can we design, apply the code, or perform troubleshooting?

Likewise, we all have a duty to participate in making the laws that we agree to honor. This means that we need to correct errors. Errors will not correct themselves.

Even within our own lifetimes there have been such errors corrected. Seatbelt interlocked ignitions and the 55mph speed limit are two examples that come to mind. Other matters are currently 'under review' by the populace; witness the continuing discord regarding both marijuana and abortion. Citizen participation is what drives all of these.

Now, regarding the AFCI, it sure looks like the basic premise behind the device has been called into question. Each of us has some opportunity to affect the adoption, expansion, and even the repeal of rules regarding the device. The "AHJ" can be many many different parties, but the NFPA certainly isn't one of them. Nor is UL or Square D.

No, the burden falls squarely on the AHJ. Those other 'interested parties' might be a useful resource, but that does not lessen the responsibility of the AHJ. Since we have set our country up as one where every AHJ derives its' authority from the consent of the governed, we all have the duty to monitor those we call "AHJ's."

IMO, Mr. Engle has certainly brought enough doubt to the table to justify suspending any AFCI enforcement until the matter is settled. Any AHJ that does not consider this matter is being irresponsible.

Don't give me the 'we're bound to enforce the law' malarky. Every bureaucracy has its' mechanisms for changing, interpreting, and enforcing the 'law.' Nor have bureaucracies had the slightest hesitation in being mighty selective in their applications; witness the current debate regarding 'pre-emption' with regard to immigration laws. On that topic, the "AHJ" has no problem ignoring one group of 'interlopers' while suing another.

"As AHJ, I have no recourse." Then you're not the AHJ. You simply represent the AHJ. If you have to do what the State tells you, then the State is the AHJ. At a minimum, you have a duty to ensure that those who adopt the rules have all the relevant information available to them. I'm pretty sure that means they have to listen to more viewpoints than just the one of the NFPA.

Likewise, we are all part of the code-making process. You know, that 'consensus-based' stuff they brag about. Some of us even are part of code panels. Well, there's a reason proposals get voted on- both in committee and on the convention floor.

These are serious matters. That's why I consider it so critical to examine Mr. Engle's paper so closely. If he's in error, we ought to be able to demonstrate the error. If he's right, the AFCI is a fraud.

This thread has examined only one of his assertions. So far, it looks like he is correct when he asserts that an 'arc fault detector' is no more possible than a time machine or anti-gravity paint.

His paper raises many other issues, each of which needs to be separately examined. I expect to see these issues raised in additional threads.

a deacade ago i had complaints of 'no load' heat emissions

conferring with one of the brighter ahj's at the time (sadly retired) i was told space them out every other breaker

this was version 1 btw

last ahj who viewed my afci packed panel said that he was unsure if the manufacturer would have wished that i uncurled the white N pigtail

it's an issue that's taken all my patience.....

~S~

Reno

perhaps the easiest avenue is to simply get Dr E's paper out there, and let the nonpartisans of the trade educate themselves and decide on a course collectively

there are a lotta ways to do this, aside form the professional forums

i'm sure i don't need to list them for anyone here

~S~

The information and data within the discussions here is being correlated and intent is to forward same to those within the code adoption offices of the state.

As we (NJ) have lagged behind the majority of the ststes in adopting AFCI requirements, perhaps those that make the choices for the people will hear this issue & act accordingly.

Amen to that HotOne

as jaded and cynical as i have grown, i still hold out for those who would promote the altristic

we were, fwiw, in Vt a code cycle ahead of the nation, because our chief inspector at the time thought the afci God's gift to the trade

so did i, for a while

i've waited almost a decade for the likes of Dr. Engle , i've stood alone before the powers that be (and let me tell you. it's mighty lonely standing up to some of the trades respected silverbacks here) lamenting them publicly

i'd like the truth, the whole truth, and nothing but the truth

(gets off stump)~S~

Reno:

I have to briefly comment here in this thread, and perhaps further via PM, email, or a venue of your choice if you care.

As an AHJ, I have no choice but to enforce the adopted codes. Yes, I may, or may not personally agree with the written word, but if I want to stay employed, I have to enforce what the state adopted.

Amending what is presently adopted is not going to be easy, perhaps IF & when the 2011 NEC is adopted, may be the next available chance, but....some things move slow.

Take care & stay safe.

"The information and data within the discussions here is being correlated and intent is to forward same to those within the code adoption offices of the state."

My point exactly. The subject has a duty to tell the Emperor when he has no clothes.

There's a section in the NEC that addresses those illuminated clothes rods. Care to guess who made the proposal? Whose reasoning was published in "Analysis?" Whose proposal was rejected, revived, rejected, accepted, deleted, then magically showed up in the NEC?

I cite that example, not to brag, but to illustrate even a nobody apprentice from the 'biggest little city' can make a difference with the NEC.

As we validate Mr. Engle's arguments, it will become ever harder for the code panel to maintain its' position. There is also no statuatory requirement that any AHJ adopt any part of the NEC- a fine point many AHJ's have forgotten.

Only in the past few code cycles has there been such a hysterical campaign by the NFPA, the IAEI, and others to urge AHJ's to accept the NEC complete, without local ammendments, in it's latest version. This campaign will face a much harder 'sell' if the AFCI is discredited, and they attempt to preserve it.

You, and others, may believe that they 'have to enforce,' but that does not mean they cannot work within the system to correct it.

Personally, I believe such folks have a greater duty than the ordinary citizen to do so.