first CAFCI install pays off two weeks later

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mark thomas

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During residential subpanel replacement installed CAFCI on kitchen light circuit. Two weeks later, breaker trips and won't reset. I isolated segments of circuit until breaker would reset and narrowed fault down to a short switch leg. Peeling back insulation revealed the rat-nibbled romex in attached pic. Presumably the CAFCI is doing its job. But nothing else has changed in the two weeks, not even a light bulb change. The rat work is old (rats exterminated a year ago). Trip happened shortly after it started raining (and foggy.) Location is not wet, but it is within inches of attic vent and basically exposed to outside air. Could it be the increased humidity?
 
AFCIs pick up an Arc signal on the sine wave. They also have a GFP function.

Do you know if it tripped due to Arcing or Ground fault?


With the moisture of the day you mentioned, I would venture to say it tripped due to GF, not arcing. Arcing generally leaves a telltale sign.
 
I assume you have replaced it, using a megger while it was still installed would have given you the best results of what was going on. after removing this cable you may have brushed off some dirt or removed insulation with semi conductive material in contact with the cable. since a mouse chewed on the cable it is possible the mouse urinated near the area which could also create a path for current flow, disturbing the installation before testing could give different test results.
 
Pierre C Belarge said:
AFCIs pick up an Arc signal on the sine wave. They also have a GFP function.

Do you know if it tripped due to Arcing or Ground fault?


With the moisture of the day you mentioned, I would venture to say it tripped due to GF, not arcing. Arcing generally leaves a telltale sign.
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Based on your post and some others I have seen I am getting the impression that you think the combination arc fault breakers are arc fault/gr fault. NOT TRUE
 
One-eyed Jack said:
According to mfg. listing the combination arc fault has the ability to detect series and parallel ARC faults as opposed to series only arc faults. There may be "some" GF function inherent in the design but that is not it's primary marketing parameter.
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As far as I know all AFCIs have GFP at 30 to 50 ma included with them. No, they are not marketed as GFP breakers but they do have GFP, that is the primary reason they trip if the neutral and EGC make contact with each other.
 
mark thomas said:
Trip happened shortly after it started raining (and foggy.) Location is not wet, but it is within inches of attic vent and basically exposed to outside air. Could it be the increased humidity?
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Sounds like condensation where the warm inside air meets the colder outside air.
 
One-eyed Jack said:
Based on your post and some others I have seen I am getting the impression that you think the combination arc fault breakers are arc fault/gr fault. NOT TRUE
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You should probably read a few of my past posts in regards to how the AFCI device operates...;)


I am willing to bet that more AFCIs trip due to the GFP function, then the Arc Fault function.

If you look at the OP's picture, there is not much, if any trace of an arc, hence my comment on the GFP function.

And
You can bet the manufacturers are not going to market the AFCI device as a GFP device. They worked like the devil to get this in the NEC long before the device had proven any merit as an AFCI device. The GFP portion is not even part of the Standard the manufacturers have to adhere to. The GFP is a 'SAVE THEIR BUTT' function.
 
Pierre C Belarge said:
You should probably read a few of my past posts in regards to how the AFCI device operates...;)


I am willing to bet that more AFCIs trip due to the GFP function, then the Arc Fault function.

If you look at the OP's picture, there is not much, if any trace of an arc, hence my comment on the GFP function.

And
You can bet the manufacturers are not going to market the AFCI device as a GFP device. They worked like the devil to get this in the NEC long before the device had proven any merit as an AFCI device. The GFP portion is not even part of the Standard the manufacturers have to adhere to. The GFP is a 'SAVE THEIR BUTT' function.
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Sounds like you are saying this is in reality a gfci device being marketed as an arc fault. "SAVE THEIR BUTT" meaning recoupe r+d on gfci by calling it combination arc fault?
 
One-eyed Jack said:
Sounds like you are saying this is in reality a gfci device being marketed as an arc fault. "SAVE THEIR BUTT" meaning recoupe r+d on gfci by calling it combination arc fault?
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I don't see where Pierre or anyone else here has stated that AFCI's also have GFCI protection. As Bob stated AFCI breakers have GFP set around 30-50ma. GFCI protection is 4-6ma. I agree with Pierre 100% about most AFCI trips are from the GFP circuitry.
 
Good point that it could be ground fault, though I thought the arc fault detection was subtle and fast enough that it would trip on small arcs that might not show obvious visual signs. Not true?

But given that this is flat romex so the bare ground is in between the conductors, it does seem like a conductor is a lot more likely to fault to ground than to the other conductor.

I didn't remove or disturb the wiring (other than removing the insulation that was over it). I just disconnected the leg at the closest junction box. So I can still test it, though as noted I don't have a megger. But there is a GFCI breaker in the panel too, so I could test it on that breaker.
 
Pierre C Belarge said:
You are putting words in my mouth.

When reading a post, try not to read more than what is written. I am pretty well known here for saying how I feel.

What I was saying is just what I wrote. ;)
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Not really putting words in your mouth. I am an opponent of the arc fault in general. The arc fault requirement has increased the cost of a 1000 sq ft home over 400.00. Based on your post it is going to trip on the gf component more than the arc fault. This makes it just another industry driven requirement that benefits industry more than the consumer. The arc fault component can not be reliably tested in the field. This means push the button on the breaker. If it trips is it good???? Put a magnet on the switch of duct smoke detectors and they will trip. Does this make it good??
 
One-eyed Jack said:
Sounds like you are saying this is in reality a gfci device being marketed as an arc fault. "SAVE THEIR BUTT" meaning recoupe r+d on gfci by calling it combination arc fault?
Click to expand...
Actually your statement has a bit of truth, but first the combination type of AFCI has nothing to do with the fact that the AFCI includes ground fault protection. The "combination" type includes more protection from "series" type faults beyond the outlet...at least that is the intent. All AFCIs include ground fault protection and I do think that was included as a CYA provision. It is much easier to detect a ground fault than it is to detect an arcing fault and with equipment that includes an EGC connection, it would be rare to have a fault that can produce enough heat to cause a fire without having a ground fault. Also the ground fault protection in an AFCI operates at a much lower fault current level than does the actual arc fault protection. Even with the combination type, the arc fault protection circuit does not even look at the arc signatures until the current exceeds 5 amps (a current 100 times greater than the GFP trip point)....with the older parallel ones, they did not look until the current exceeded 75 amps.
In talking with one of the lead CH AFCI product engineers at a trade, show his estimate is that for actual AFCI fault trips, it is the GFP that opens the circuit about 90% of the time ....for the trips that are caused by installation errors, the GFP part opens the circuit almost every time as the common installation errors create ground faults and not arc faults.
 
don_resqcapt19 said:
Actually your statement has a bit of truth, but first the combination type of AFCI has nothing to do with the fact that the AFCI includes ground fault protection. The "combination" type includes more protection from "series" type faults beyond the outlet...at least that is the intent. All AFCIs include ground fault protection and I do think that was included as a CYA provision. It is much easier to detect a ground fault than it is to detect an arcing fault and with equipment that includes an EGC connection, it would be rare to have a fault that can produce enough heat to cause a fire without having a ground fault. Also the ground fault protection in an AFCI operates at a much lower fault current level than does the actual arc fault protection. Even with the combination type, the arc fault protection circuit does not even look at the arc signatures until the current exceeds 5 amps (a current 100 times greater than the GFP trip point)....with the older parallel ones, they did not look until the current exceeded 75 amps.
In talking with one of the lead CH AFCI product engineers at a trade, show his estimate is that for actual AFCI fault trips, it is the GFP that opens the circuit about 90% of the time ....for the trips that are caused by installation errors, the GFP part opens the circuit almost every time as the common installation errors create ground faults and not arc faults.
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I agree. That is the point I was making in a very simplified post. Combination is indicative of the parallel/series capability and is marketed as such.
 
I don't think I entirely understand the critique of the CAFCI here (I am not disagreeing, just trying to understand.) I get that, in general, there's offense at the self-interested industry tactics. But setting that aside for the moment, what are the other criticisms? Does anyone claim it's 100% hype, and CAFCI's are good for nothing?

Most seem to agree that it's the GFP component of CAFCI's that fires "most" or even "90%" of the time, but so what? Isn't it a good thing to detect those ground faults, and also to detect the 10% (or whatever) occurrences that are actually arc faults?

Or is the critique just that its detection of real arc faults is so rare that it doesn't justify the expense?

What I also don't understand with respect to industry/marketplace is why they make CAFCI's ground fault at 50ma instead of GFCI standard of 5ma. Is there a specific desire to allow some ground leakage in applications where CAFCI's would be spec'ed? (seems not very likely.) I guess I don't understand what the SAVE THEIR BUTT purpose Pierre refers to. I'll search some past posts and try to see if I can answer my own question.

If the CAFCI's were less expensive than GFCI's, it'd make marketing sense that the manufacturers would not want to undercut the GFCI market, but that's not the case, in fact, CAFCI's are more expensive. If a CAFCI worked as a GFCI, you'd presumably get some people "upgrading" to CAFCI where GFCI required and CAFCI not required (garage, exteriors) and this would be profitable to makers, unless the issue is that the margins are on GFCIs are much greater than on CAFCI's.
 
I wont criticize the industry at this time. This is what I see the arc-fault doing to the residential market. Take a 1200 sq ft house. To meet min NEC the gen purpose requirement can be met with 4-1500 watt circuits. This means all the lights and all of the recp except the 2 small appliance can be put on these 4 circuits. What I have been seeing for the past 40 years is 10-14 circuits doing this job. You are going to see the number of circuits decline toward the minimum because of the price. 10x40 = 400.00 cost to install the extra circuits. You now have a min. capability and/or compliance. Thru special purpose outlets you have increased the cost to the consumer with little increase in safety and a likely reduction in usability due to the fewer circuits. Wired properly there will be no need for extension cords so IMO the value of the arc fault is reduced. Educate the consumer in the proper use of electrical equipment instead of assuming that the are too stupid and you must protect them from themselves even if it means bankrupting the economy.
 
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