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

[Strife]

I have no problem with arc fault protection. If I ever see one.
I just feel this was shoved down our throats with very little testing for actually making it work.
How exactly do you detect an arc 5 feet away from the connection point? I know enough about electricity to know you can't. You can compare the current going in VS the current coming back (GFCI anyone?), you can even measure a lot of other things, but I still can't figure how can you measure an arc? If there was to be a true arc fault, there would have to be a thermal sensor along the whole length of the conductor all the way into the TV (let's say it). Not only that, but the said sensor would have to be able to detect difference of temperatures between 3' and 5' (otherwise we're just having a glorified overload protection). That's really the only way I can see an arc fault protection working. After all the temperature where the arc takes place would be higher than the rest of the conductors. That's the way I see it, someone prove me wrong. NO "because it has been blah blah blah". Someone please show me how exactly these "AFCI's" work.

 

[iwire]

There is no doubt at all you can detect an arcing condition. The real question is can you do it in the space of a typical breaker and for a realistic price?


As far as the how, you would measure current and voltage changes and when they were changing in a specific way you would know an arc was happening ......... or a vacuum cleaner motor was running.

 

[raider1]

HERE is a link to a NEMA site with FAQ's regarding AFCI's.

Chris

 

[Strife]

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?

HERE is a link to a NEMA site with FAQ's regarding AFCI's.

Chris

 

[Nium]

My experience

My experience

I installed CAFCI on Al branch circuits because the homeowner had a receptacle melt and cause a small fire because of well because of AL branch circuits. A few weeks later they called me back saying the CAFCI on 1 circuit kept tripping. The standard breaker didn't trip. They wanted to know if I would put back in the regular breaker. I explained the CAFCI was doing it's job and went over to trouble shoot the circuit. The problem was an installation for a ceiling fan (non-electrician had done years ago) had copper to aluminum conductors which in and of itself was a problem but the installer hadn't twisted the wires together at all and in checking the junction box I pulled a wire nut off by moving it to better see into the box. The poorly made splices were arcing inside the wire nuts which led to the CAFCI breaker tripping. I feel that if the CAFCI breaker hadn't been installed and worked then the poorly made splices would have eventually led to a fire. A standard breaker wouldn't have tripped or opened the circuit till the insulation melted off the conductors and a short was created. For me that was a real world instance where the CAFCI worked and prevented loss that a standard breaker may not have.

 

[Strife]

So you would do it like my credit cards?
Based on spending patterns?\
1: Not realistic.
2: that would require a computer inside the breaker.
Yes, you can detect an arc, I just don't see it without an additional wire to sense the temperature along the length and send information for every foot in the length.

There is no doubt at all you can detect an arcing condition. The real question is can you do it in the space of a typical breaker and for a realistic price?


As far as the how, you would measure current and voltage changes and when they were changing in a specific way you would know an arc was happening ......... or a vacuum cleaner motor was running.

 

[Dennis Alwon]

2: that would require a computer inside the breaker.

There is a chip inside the Breaker. It monitors the sine wave. When the sine wave gets hairy it knows.

 

[Dennis Alwon]

Here is something I found online.

Basically - The arc fault circuit breaker continuously monitors the shape of the sine wave of the electricity passing through the AFCI breaker. Anytime the sine wave is uneven or jagged, there may be a sparking condition somewhere down the line. In this case the AFCI breaker will click off. Most of them also will light one or two tiny LEDs on the front of the breaker. By reading the instructions you can determine if it was a hot-to-ground fault or a hot-to-neutral fault.

The AFCI uses a very simple computer chip that constantly checks for a sparking condition between the hot wires and the neutral wire. It also checks for a high resistance or over heating condition in either the out going hot wire or the returning neutral wire.

Generally it checks for any sputtering, sparking or overheating condition that might indicate a loose or overheating connection.

 

[Nium]

2: that would require a computer inside the breaker.

There are microprocessors in CAFCI and AFCI breakers. The breaker monitors the sine wave to determine if arc fault conditions are present. A sine wave during an arc fault is not smooth and will have "fuzziness" to it. When the breaker monitors an arc fault for a certain period it will open the breaker. The breaker is suppose to be able to tell the difference between normal arc conditions (vacuum cleaner, switch opening or closing, etc.) and arc fault conditions. The microprocessor is not detecting changes in temperature but is monitoring the sine wave.

Computer chips are tiny here's a link to a picture of an example
http://www.techepics.com/files/smallest_camera_chip.jpg

 

[ELA]

There is a chip inside the Breaker. It monitors the sine wave. When the sine wave gets hairy it knows.

Here is a post where I explained in a little more detail how the QOAFCI works:
There is a scope trace showing all the "hair" on the sign wave

http://forums.mikeholt.com/showthread.php/111163-AFCI-Test-Button-What-does-it-do/page3?highlight=AFCI

My testing at the time was only on a QO breaker and it is clear that not all AFCI's are created equal.

For sure they have a long way to go to be truly immune to false tripping. That may be too cost prohibitive for general use. They were surely forced on us before they were ripe.

 

[iwire]

So you would do it like my credit cards?
Based on spending patterns?

Great anolgy and the answer is yes ... like that.

2: that would require a computer inside the breaker.

Computer? No, processor yes.

Yes, you can detect an arc, I just don't see it without an additional wire to sense the temperature along the length and send information for every foot in the length.

You may not see it but it can be done without all of that.

Have you had any experience at all with an oscilloscope?

 

[iwire]

There is a chip inside the Breaker. It monitors the sine wave. When the sine wave gets hairy it knows.

Nicely put and I agree with it.

 

[ELA]

Computer? No, processor yes.

Technically what is used is more like a computer on a chip. They are referred to as a microcontroller. The microcontroller contains a processor, memory, digital and analog I/O, communications interfaces etc.
The microcontroller used in the QOAFCI is a PIC24FJ64GA in case anyone should be interested.

 

[al hildenbrand]

Someone please show me how exactly these "AFCI's" work.

I wish I could answer that question myself.

AFCI manufacturers have given us jingoism and evasions 99+% of the time, inspite of our clamour for hard tech information.

I did, however, find some very useful insight into AFCI arc discrimination theory in a white paper written by Carlos Restrepo, a Siemens engineer. It's 8 pages long, and was presented at the IEEE Holm Conference back about three years.

Admittedly, the paper doesn't describe a specific CAFCI that I can hold in my hand, but it does give the reader an idea of what the AFCI is doing prior to trip. As a result of reading this white paper, I have come to think of the AFCI detection circuitry as a signal processor, more than anything else.

Holm Conference AFCI paper

Strife, give this a slow deliberate read and it should go a long way to help. I know it did for me.

 

[SAC]

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).

 

[don_resqcapt19]

...as well as appliance manufactures having to design them so that they won't trip the arc faults).

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.

 

[bluesmoke...oops]

It is my opinion the issue is up to the AFCI manufacturers to solve.

I agree. They should make their product compatible with existing equipment.

 

[SAC]

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.

I agree, but if people keep returning your appliances to the store because they can't use them in their house you need to do something to stay in business! What are are you going to do, tell the customer to remove the arc faults? Having an "arc fault friendly" appliance starts to become a competitive advantage...

 

[bluesmoke...oops]

What are are you going to do, tell the customer to remove the arc faults? Having an "arc fault friendly" appliance starts to become a competitive advantage...

So because by code the homeowner was forced to install what amounts to a defective product, all appliance manufacturers should spend untold amounts of time and money to change the designs of their products to work with this defective product? Just wanting to be clear that is what you are saying.

And "competitive advantage" translates to "costs more"

 

[SAC]

So because by code the homeowner was forced to install what amounts to a defective product, all appliance manufacturers should spend untold amounts of time and money to change the designs of their products to work with this defective product? Just wanting to be clear that is what you are saying.

And "competitive advantage" translates to "costs more"

I think you are putting me on the wrong side. I'm not saying "should", I'm saying "forced". Let's say you have been selling a great vacuum for years. Good seller, good revenue. Now all of a sudden the field returns start to go up and sales decline. Why? Because people are returning them because they are tripping AFCIs. 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 (or both). Meanwhile there are other company's vacuums that don't seem to have the same issue, and people are buying them instead. If it was your business, would you say forget looking into a design change and let's bet on changing the government regulations? If it were me calling the shots, I certainly wouldn't bet my business on changing the code unless there was no other reasonable way out. Bottom line is it doesn't matter if the AFCIs are useless or great - your business is at stake and you do what is in your power to rectify your revenue problem.