'Proof' that AFCI devices really locate arcs.

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K8MHZ

K8MHZ

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Michigan. It's a beautiful peninsula, I've looked
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Electrician
Has anyone here actually found evidence of an arc that was revealed by the tripping of an AFCI?

As an example, AFCI trips. After some searching, a loose connection that has evidence of arcing is located and repaired. AFCI now operates without tripping.

What I am not asking for is faults located that have no evidence of arcing. By evidence, I mean burnt metal. Not just a ground and neutral touching that would trip a GFCI.

Over the years I have seen many arc faults. I kept some of the more dramatically affected devices. I have wondered if an AFCI would have detected the arcs, as none of the arc faults I have ever seen had AFCI protection.

Thanks
 
Nutmegger said:
Had a customer whose AFCI was tripping many times a day, and discovered it to be their MacBook power adapter arcing on the low voltage side b/c of a frayed wire.
The AFCI's were GE.
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An AFCI detected an arc through an AC-DC power supply, presumably a switchmode power supply? I'm not questioning that it happened, but rather should it happen.
 
epimetheus said:
An AFCI detected an arc through an AC-DC power supply, presumably a switchmode power supply? I'm not questioning that it happened, but rather should it happen.
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Yes, it was a switchmode supply.
It may not be apparent from my first post, but I was surprised too.

Replicating the trip was easy -- just wiggling the low voltage side cord would make the breaker trip quite predictably (about 3 out of 5 times).
And it wasn't the case of a backstabbed or otherwise bad receptacle -- this would happen in with any receptacle on that circuit, or any of the two other AFCI circuits in the house.

Before I go praising GE though, I should say that those AFCI's were also nuisance tripping quite a bit, mostly from vacuums or Christmas lights.
 
Nutmegger said:
Yes, it was a switchmode supply.
It may not be apparent from my first post, but I was surprised too.

Replicating the trip was easy -- just wiggling the low voltage side cord would make the breaker trip quite predictably (about 3 out of 5 times).
And it wasn't the case of a backstabbed or otherwise bad receptacle -- this would happen in with any receptacle on that circuit, or any of the two other AFCI circuits in the house.

Before I go praising GE though, I should say that those AFCI's were also nuisance tripping quite a bit, mostly from vacuums or Christmas lights.
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Something to consider.

The shield of the low voltage cable is connected to the EGC through the power supply. A short to the cable would produce a ground fault easily detectable from the 120 volt side which would trip a GFCI.

To think an arc signature would be detectable through the electronics of a power supply is questionable. At least to me. Do you know if the AFCI also had ground fault protection, like many do?

Oh, and thanks for you input. Real world info beats math and controlled lab results in my book.
 
K8MHZ said:
Something to consider.

The shield of the low voltage cable is connected to the EGC through the power supply.
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How so? Many power supplies like this are connected to power though a two prong plug (no ground pin), and some of them are unpolarized.
 
The theory about the shield of the power supply is a valid one, but in this case it was a regular 2-prong Apple MacBook power supply.
HP's, Dells and other Windows-based machines mostly come with 3 prongs DC adapters, but Apple's is 2-prong;
At least if you don't use the line-side extender cord that they give you; This customer was not using the extender, just the 2-prong "switchblade" block.
There was no apparent short between the wires on the low-voltage side (although there could be), but there quite possibly was a series arc there somewhere.
How did that signature get through the circuitry to the line voltage side is anyone's guess.
 
Nutmegger said:
The theory about the shield of the power supply is a valid one, but in this case it was a regular 2-prong Apple MacBook power supply.
HP's, Dells and other Windows-based machines mostly come with 3 prongs DC adapters, but Apple's is 2-prong;
At least if you don't use the line-side extender cord that they give you; This customer was not using the extender, just the 2-prong "switchblade" block.
There was no apparent short between the wires on the low-voltage side (although there could be), but there quite possibly was a series arc there somewhere.
How did that signature get through the circuitry to the line voltage side is anyone's guess.
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Thanks. I see that on the schematics. No connection to EGC anywhere.
 
big john said:
I was curious about the same thing, so I started this poll thread a while back.

Apparently some guys have definitely found what looked like arcing faults with them. I know in my case I only ever saw GFP trips.
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I agree as my experience and bee that the GF feature of the AFCI was a cause of trip. i'm still waiting for the insurance industry to respond by singing their praises because they have found that the AFCIs in fact have saves lives as well as property. As such would anticipate that the insurance companies would provide some sort of financial incentive in new construction as well as there being used replacements in older structures.
Even though I believe in AFCIs I've stopped holding my breath that the would be recognized by the insurance companies and now question that they in fact are benificial. Yes, I am disappointed.
 
templdl said:
Even though I believe in AFCIs I've stopped holding my breath that the would be recognized by the insurance companies and now question that they in fact are benificial. Yes, I am disappointed.
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I keep thinking that someone from NEMA will land on an aircraft carrier with a big sign " Mission Accomplished". It's been done before. :lol:
 
Everyone that has ever complained to me about one, has gone back and found a staple driven in too hard, a pinched wire or a nail or something to that affect.
 
cowboyjwc said:
Could be, but do you know for sure or are you just guessing?
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Unless you have an AFCI that tells you what the trip was, everyone is guessing. It could be an overload, a short circuit or high current ground fault, a low current ground fault, an arcing fault (assuming they even exist at dwelling unit voltages) or is just tripped because it wanted to.

That being said, I have had some discussions with AFCI design engineers and they believe that 80% or more of the trips are ground fault trips. Many of those from poor wiring practices.
 
don_resqcapt19 said:
Unless you have an AFCI that tells you what the trip was, everyone is guessing. It could be an overload, a short circuit or high current ground fault, a low current ground fault, an arcing fault (assuming they even exist at dwelling unit voltages) or is just tripped because it wanted to.

That being said, I have had some discussions with AFCI design engineers and they believe that 80% or more of the trips are ground fault trips. Many of those from poor wiring practices.
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So if we're just guessing, then what's the argument?
 
cowboyjwc said:
Could be, but do you know for sure or are you just guessing?
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I can't know for sure, only the person who diagnosed it would know that.

But seeing how I know those types of faults will trip GFCIs, and seeing how I've personally diagnosed similar AFCI trips that proved to be ground faults, I'm comfortable making that argument.
 
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