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Discussion Starter · #1 ·
How well do afci's protect old two wire circuits during arc events? I am aware of their inability to protect against "glowing" connections. I've read competing arguments for and against their ability to work with 40's era two wire circuits.
 

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I had not heard arguments that a 2 wire circuit will not benefit from an afci. I can't imagine that it would not benefit and I don't see why it wouldn't work fine.
 

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Discussion Starter · #3 ·
I had not heard arguments that a 2 wire circuit will not benefit from an afci. I can't imagine that it would not benefit and I don't see why it wouldn't work fine.
so you would agree that they protect against series and parallel arcs
in older wire where the insulation is cracking, etc.?
 

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It is my opinion that most of the work done by the AFCIs is done by the ground fault detection circuit and you are less likely to have a ground fault if you have a two wire system.

As far as protection from arcing faults, I can find no technical information that says a sustaining arcing fault is even possible at dwelling unit voltages.
 

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It is my opinion that most of the work done by the AFCIs is done by the ground fault detection circuit and you are less likely to have a ground fault if you have a two wire system.

As far as protection from arcing faults, I can find no technical information that says a sustaining arcing fault is even possible at dwelling unit voltages.
We have had this discussion before and Don is probably correct however Ge and now Siemens do not have gfp in their afci breakers anymore. I however think that there is some benefit as I have seen GE afci work where their were issues.

In answer to the question about insulation cracking etc. You may have a lot more nuisance faults in an old 2 wire system with the cracking insulation but supposedly these devices should protect from those faults. I like Don have no substantiation as to whether they are effective . I have read some info that says the gfp in combo with the afci does a better job of protecting the cir.

Here is an interesting read on afci http://www.combinationafci.com/resources/doc_iee_paper_presentation_orlando_2012_02_03.pdf
 
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Discussion Starter · #6 ·
As far as protection from arcing faults, I can find no technical information that says a sustaining arcing fault is even possible at dwelling unit voltages.
If this is so, one could argue that rewiring a house with rotting insulation in their outlet boxes could be deemed unnecessary. In addition, I was mistaken that afci's can detect series arcing, according to an IAEI article I am currently perusing.
 

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If this is so, one could argue that rewiring a house with rotting insulation in their outlet boxes could be deemed unnecessary. In addition, I was mistaken that afci's can detect series arcing, according to an IAEI article I am currently perusing.
I didn't say wiring problems don't cause fires...I just said that a fire causing self sustaining arc is not possible at dwelling unit voltages.
A glowing connection is not an arc and can start fires. A short can throw sparks that can cause fires. There are other electrical faults that can cause fires, I just don't see any solid evidence that the AFCI can prevent these fires.
 

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...I however think that there is some benefit as I have seen GE afci work where their were issues....
What were those?

My experience with AFCIs has been 100% ground-fault trips.

I think I've seen one thread on an internet forum where a guy had an obvious arcing fault and the AFCI caught it, but I believe he said a normal breaker did not. That is literally the only example I can point to where AFCI technology may have played a role in preventing a hazard.
 

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What were those?

My experience with AFCIs has been 100% ground-fault trips.

I think I've seen one thread on an internet forum where a guy had an obvious arcing fault and the AFCI caught it, but I believe he said a normal breaker did not. That is literally the only example I can point to where AFCI technology may have played a role in preventing a hazard.
John it was not necessarily a situation of an arc from a bad connection but rather from a tv or fan where the afci would trip. I am assuming if it sees that arc signature it would also see other arc signature and trip. I may not be correct but that was my assumption.

Even if the afci does not work to perfection it can also help us find bad wiring that was made that would otherwise go unnoticed. It has some value-- I am not convinced about them but it is what it is so I deal with it.
 

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Discussion Starter · #10 · (Edited)

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So a self sustaining arc is not a glowing arc? I'm just trying to fully understand terminology being used here.
Testing labs do practice such events and apparently they apply to real world conditions.
Good article here: http://www.iaei.org/blogpost/890108...ns-for-Fires-Resulting-from-Electrical-Arcing
A glowing connecting is not an arc...it is just a high resistance connection ... not really any different than the heating element in your toaster. Even the UL information, if you dig deep enough, says that AFCIs cannot directly detect a glowing connection or as they sometimes call it joule heating.
The following is from a UL test report on aged and damaged NM cable.
To evaluate the probability of arcing when NM cables have lowered breakdown voltages, hammer-damaged and aged NM cable samples were tested per UL1449 (Standard for Surge Protective Devices). This test showed despite a breakdown voltage lower than the surge voltage (using 6kV surges on samples with breakdown voltages below 5kV), 9% of the hammer-damaged and 2% of the hammer-damaged and then aged samples exhibited arcing after the surge occurred. All of these observed arcs were approximately 1.7ms in duration, meaning that the arcing was longer than the surge event (i.e., supplied by 120VAC), but self-extinguished within a single AC half-cycle. These events did not have enough energy to ignite NM cable insulation and were not sustained for more than one half-cycle, a duration that is not expected to trip an AFCI and is shorter than the UL1699 eight half-cycle criterion. To evaluate whether subsequent damage would increase arcing duration or sustainability, samples were tested using 300 voltage surges to understand how likely the repeated voltage surge and arcing may result in sustainable arcing and ignite the NM cable insulation. But these tests did not show any sustained arcing.
 

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A glowing connecting is not an arc...it is just a high resistance connection ... not really any different than the heating element in your toaster. Even the UL information, if you dig deep enough, says that AFCIs cannot directly detect a glowing connection or as they sometimes call it joule heating.
The following is from a UL test report on aged and damaged NM cable.

When I was just a wee lad, we were playing cards in my neighbors basement, his mother turned on the cloths dryer in the kitchen, the inrush-current made the K&T wire glow like a toaster:eek::laughing: They had an electrical fire a few years later, AFCI breakers would have done nothing because of the overloaded circuits created by the home owner..
 

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When I was just a wee lad, we were playing cards in my neighbors basement, his mother turned on the cloths dryer in the kitchen, the inrush-current made the K&T wire glow like a toaster:eek::laughing: They had an electrical fire a few years later, AFCI breakers would have done nothing because of the overloaded circuits created by the home owner..
When you were a wee lad that K&T was probably fed from a fuse panel and those pesky fuses probably had a penny behind them to save money. I would think an AFCI would have prevented such an event because the overload would have tripped a circuit breaker assuming it is sized properly.
 
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