GFCI protected circuits

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RFGuy
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Re: GFCI protected circuits

Post by RFGuy »

JPG wrote: Mon May 03, 2021 10:47 am I am curious how a capacitor by itself performs a LOW pass function?
If I were trying to solve the EMI concerns for the PowerPro, I would buy/design an LC filter for the input, but regarding the published paper referencing a 1uF lowpass, I can't say for sure what their intent is since I don't think enough details of their setup is shared in their paper. However adapting it to discuss regarding the PowerPro, there could be enough R and L in the line between the breaker and the PowerPro that adding an input cap could create a sufficient lowpass filter (using the parasitics in the house wiring).
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JPG
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Re: GFCI protected circuits

Post by JPG »

I consider a "C" across the input(Hot - Neutral) to be a High Pass Filter effectively snubbing the high Frequency stuff.
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RFGuy
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Re: GFCI protected circuits

Post by RFGuy »

JPG wrote: Mon May 03, 2021 11:20 am I consider a "C" across the input(Hot - Neutral) to be a High Pass Filter effectively snubbing the high Frequency stuff.
??? A shunt capacitor will have low reactance to higher frequencies so it will shunt them from the hot to the neutral. This is a low pass function because low frequencies get through and high frequencies are shunted to netural in this case.

So, I dug up some more AFCI information that I think sheds more light on how they function and why a PowerPro might trip one. Below is the block diagram for what is happening in an AFCI. In the excerpt from this below you can see that the key point of how "bad" arcs are determined by an AFCI is by looking at whether the waveform is periodic or not. So, a well behaved brushed motor might be seen as a "good" arc, but asynchronous switching waveforms backfed into the supply line from a PowerPro could be perceived as a "bad" arc. Also spurious harmonics (from a PowerPro) being fed back could also trip the "bad" arc signature circuitry, I suspect.

Except from paper linked below:
A major design consideration was the ability of the AFCI to discriminate between “good” and “bad” arcs. “Good” arcs are characterized by being periodic or repetitive (occur each 60 Hz cycle) and can be non-sinusoidal. “Bad” arcs are characterized by non-periodic or non-repetitive waveforms.

AFCIs use electronic detection circuits to discriminate between good and bad arcing conditions. Once an unwanted arcing condition is detected, the control circuitry in the AFCI trips the internal contacts, thus de-energizing the circuit and reducing the potential for a fire to occur. Methods for the detection of “bad” arcs include looking at certain frequencies, discontinuities, and inconsistencies in the current waveform. For detection, both magnitude and duration of a particular half cycle are required. Some detection algorithms also look at rising or falling edges of an arcing current for their detection criteria. The industry voluntary standard for AFCIs requires a trip if 8 half cycles of arcing occur within a 0.5 second window.

AFCI.pdf
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DLB
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Re: GFCI protected circuits

Post by DLB »

Combined breakers providing GFCI and AFCI are becoming popular for various reasons, even where only one type of protection is required. Hypothetical case: Garage receptacles require GFCI (true for decades) but has both AFCI and GFCI at the breaker, under warranty. PowerPro, under warranty, trips breaker. Who is paying for fault isolation, and corrective action? Automatic answer from these people is call electrician. Appears to me to require an oscilloscope with a current probe and ability to view per-trigger events (common now in digital scopes), knowledge of how the PowerPro should work, and knowledge of how the CB does work. Electricians, in my experience, might not be qualified to perform the relatively simple task they have. (Though they can occasionally pass a test on it.)

(Note - I have this exact case on the house I'm in the process of buying, except strike PowerPro and replace with Septic System. Septic, like a garage, requires GFCI but they don't have any GFCI-only breakers so it is on AFCI/GFCI. It is hard-wired so can't use GFCI outlet. Didn't trip the regular breaker they had it on when they were ignoring code. Didn't trip AFCI-only when they tried one. They are completely lost, and asking me as the prospective buyer for help. I think that's because they'd like me to tell them not to follow code. Nuisance fault? Maybe. Ground Fault? Seems likely. If no one was looking would the electrician follow code? Clearly not.)

- David
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Re: GFCI protected circuits

Post by RFGuy »

David,

It is a bit of a grey area, but I thought sump pump type applications are exempt from AFCI or GFCI requirements in the NEC. Presumably the septic application you mentioned falls under the same category as a sump pump. It should be reasonably safe to leave it on a regular CB if this is the case.
Having said this though, I don't know why a sump pump motor would trip it unless it has an internal problem. It was my understanding that these types of motors are almost always double insulated internally so in theory they should be next to impossible to trip a GFCI under normal circumstances. You didn't give specifics, but what kinds of tripping are they experiencing with the septic system and a GFCI or AFCI breaker?
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Re: GFCI protected circuits

Post by paulrussell »

An inline capacitor is high pass.
A capacitor to ground is low pass.
An inline inductor is low pass.
An inductor to ground is high pass.
DLB
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Re: GFCI protected circuits

Post by DLB »

RFGuy wrote: Mon May 03, 2021 2:52 pm David,

It is a bit of a grey area, but I thought sump pump type applications are exempt from AFCI or GFCI requirements in the NEC. Presumably the septic application you mentioned falls under the same category as a sump pump. It should be reasonably safe to leave it on a regular CB if this is the case.
Having said this though, I don't know why a sump pump motor would trip it unless it has an internal problem. It was my understanding that these types of motors are almost always double insulated internally so in theory they should be next to impossible to trip a GFCI under normal circumstances. You didn't give specifics, but what kinds of tripping are they experiencing with the septic system and a GFCI or AFCI breaker?
Sump pump, septic aerator, and septic pump all require GFCI (not AFCI YET), new features as of NEC 2020. The sump and septic requirements are in different sections, but both previously required a TM CB. Communications with the 'electrician' (meaning perhaps not licensed himself) on hand were difficult. We didn't speak the same language and the builder we were communicating through didn't really understand the technical language. So, I couldn't really determine if the breaker that tripped had a way to differentiate faults (like the flashing LED discussed earlier) or what it was attempting to communicate. Overly simplified logic: TM didn't trip, AFCI didn't trip, GFCI-only not available, AFCI/GFCI did trip. The only thing completely different is the one that tripped includes GFCI. They are trying to find a GFCI-only breaker and get the licensed electrician out there now. I explained the flashing LED thing and said there should be a manual there somewhere, but they couldn't find a manual or a breaker PN. I'm going to look for that on-line anyway, probably matches the key you posted earlier. If I was working on it the first thing I'd do is disconnect the septic system to isolate the problem between the electrical and septic systems just to get the right tech out there. That's easier in this case than in my PowerPro hypothetical.

- David
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Re: GFCI protected circuits

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DLB wrote: Mon May 03, 2021 4:07 pm Sump pump, septic aerator, and septic pump all require GFCI (not AFCI YET), new features as of NEC 2020. The sump and septic requirements are in different sections, but both previously required a TM CB. Communications with the 'electrician' (meaning perhaps not licensed himself) on hand were difficult. We didn't speak the same language and the builder we were communicating through didn't really understand the technical language. So, I couldn't really determine if the breaker that tripped had a way to differentiate faults (like the flashing LED discussed earlier) or what it was attempting to communicate. Overly simplified logic: TM didn't trip, AFCI didn't trip, GFCI-only not available, AFCI/GFCI did trip. The only thing completely different is the one that tripped includes GFCI. They are trying to find a GFCI-only breaker and get the licensed electrician out there now. I explained the flashing LED thing and said there should be a manual there somewhere, but they couldn't find a manual or a breaker PN. I'm going to look for that on-line anyway, probably matches the key you posted earlier. If I was working on it the first thing I'd do is disconnect the septic system to isolate the problem between the electrical and septic systems just to get the right tech out there. That's easier in this case than in my PowerPro hypothetical.

- David
David,

Do you know what the AFCI/GFCI breaker is that tripped on the property? Was it the one you posted about earlier? I don't know the exact part #, but the CH (Cutler-Hammer) series from Eaton similar to what you posted before at Home Depot should follow what is in the instructions linked below. There are instructions on page 5 for how to get the trip code to display (not automatic) and the code resets 2 hours after it happened so you have to check it soon after it trips. This is the only Eaton document that I could find on this series AFCI/GFCI breaker from Eaton and it still only shows 6 trip codes, not 7, but perhaps there is a newer document coming eventually. Don't know if this helps you or not, but thought I'd give it a shot. Yeah, for something like this I think they have to fix it especially if you are looking to buy the property. If only GFCI is required per latest NEC in that area then that is all they need to do, but it sounds like there is a good possibility of current leakage in the septic equipment causing a discharge. More than likely they will need to replace the equipment and not just the breaker, but that is just my guess... There was an interesting 2 star review for the breaker at Home Depot that you posted. Sounds like it still has issues, including that the fault LED looks like it is tripped when it is not (could this be what is happening there?) See below:

Definitely don't get any nuisance trips with the new Gen 6 rev, but about half of these have an error where the fault LED stays lit continuously. Eaton says this is a cosmetic defect in their breakers, but it does not affect their functionality. I have tested and confirmed this, but for a $60 breaker I expect better quality, especially for a CH (Cutler-Hammer) product. I would seriously hope they're already working on another revision to eliminate this. I would also like to know what in the current revision caused this error as it was not in previous generations, up to and including the 2019 release. The problem didn't start until the late 2020 revision.
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DLB
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Re: GFCI protected circuits

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RFGuy wrote: Mon May 03, 2021 5:51 pm Do you know what the AFCI/GFCI breaker is that tripped on the property? Was it the one you posted about earlier? I don't know the exact part #, but the CH (Cutler-Hammer) series from Eaton similar to what you posted before at Home Depot should follow what is in the instructions linked below. There are instructions on page 5 for how to get the trip code to display (not automatic) and the code resets 2 hours after it happened so you have to check it soon after it trips. This is the only Eaton document that I could find on this series AFCI/GFCI breaker from Eaton and it still only shows 6 trip codes, not 7, but perhaps there is a newer document coming eventually. Don't know if this helps you or not, but thought I'd give it a shot. Yeah, for something like this I think they have to fix it especially if you are looking to buy the property. If only GFCI is required per latest NEC in that area then that is all they need to do, but it sounds like there is a good possibility of current leakage in the septic equipment causing a discharge. More than likely they will need to replace the equipment and not just the breaker, but that is just my guess...
They are "BR" series breakers and load center. I'm told that replacing the AFCI/GFCI with GFCI only worked. Which does not make obvious sense but, it worked and meets code. The BR AFCI and AFCI/GFCI units all flash codes, so there is at least some similarity to the document you sent earlier. The GFCI-only model just trips as far as I can tell, so you would not know if it was OC or GF that tripped it. I was not successful communicating the utility of reading the code to those working on the problem. They left the questionable AFCI/GFCI breaker behind, I may test it at some point. I will definitely get the code tables for the breakers I'll actually have. While trying to verify the some of their work I tripped some of the AFCI/GFCI breakers with my tester. They flashed a code upon reset. Five flashes, consistent with the table you posted earlier for a GF.

- David
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Re: GFCI protected circuits

Post by RFGuy »

DLB wrote: Tue May 04, 2021 11:18 pm They are "BR" series breakers and load center. I'm told that replacing the AFCI/GFCI with GFCI only worked. Which does not make obvious sense but, it worked and meets code. The BR AFCI and AFCI/GFCI units all flash codes, so there is at least some similarity to the document you sent earlier. The GFCI-only model just trips as far as I can tell, so you would not know if it was OC or GF that tripped it. I was not successful communicating the utility of reading the code to those working on the problem. They left the questionable AFCI/GFCI breaker behind, I may test it at some point. I will definitely get the code tables for the breakers I'll actually have. While trying to verify the some of their work I tripped some of the AFCI/GFCI breakers with my tester. They flashed a code upon reset. Five flashes, consistent with the table you posted earlier for a GF.

- David
David,

The previous document I shared here covered the Eaton BR breakers as well as the Eaton CH ones so the same table of LED codes should apply for each. As long as it holds (doesn't trip) on a GFCI breaker I would think you are reasonably safe. Presumably the GFCI breaker is good so there shouldn't be any ground fault condition. So, a GFCI has to trip on a leakage current as small as 6mA, but they are permitted several seconds to decide at that level. However, in the 20-30mA range of leakage current, GFCI's typically trip in 25ms or so. I mention this because I believe AFCI's are designed to trip in the 30mA range of leakage current (not lower). So, to a 1st order if the GFCI doesn't trip then most likely it isn't a leakage current causing it, but some other fault condition. I know AFCI's also have short circuit protection built in, I believe. This also applies to high inrush current which could trip an AFCI's short circuit protection. I don't know for sure, but presumably this is a "feature" that AFCI's have that GFCI's don't? So it is possible there is an arc-like event, e.g. high inrush current of motor turning on, etc. that is tripping the AFCI in the house you are interested in. Lastly, the AFCI is supposed to be able to detect a few different faults in house wiring. I thought the GFCI was similar in this regard and supposed to detect a neutral tied to ground at the load, but maybe there is some mis-wiring in the septic wiring causing the AFCI to detect it and trip where a GFCI is fine with it. If there are any other branch circuits sharing a neutral, I believe this will set off the AFCI as well. Below are a couple of articles that discuss troubleshooting an AFCI that trips when a GFCI doesn't that you might find useful. If you buy the house and move in, you could try installing the AFCI breaker and split up the loads tied to it in order to isolate where the problem is coming from (if you want it to be on an AFCI). Their electrician should have tried this.
AFCITripping.pdf
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Sq-D-AFCI-Info.pdf
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