20/2 AFCI in 3 phase application

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Hi all, first post here. I have been scouring the web this morning trying to find an answer to this question (a project is on hold over it). I cannot find any discussion about using 2-pole AFCI breakers in a 3 phase situation. I have a remodel with the small appliance circuits on a shared neutral. An alteration to the circuit means it now requires AFCI protection. The test button doesn't cause the breaker to trip (instantly failed inspection), and the contractor who installed it says it's because of the 3 phase application.
Any input?

Daniel
 

david

Senior Member
Location
Pennsylvania
It’s not clear to me from your post if your multi- wire branch circuit on a three phase system evolves two of the three phases or just two small appliance branch circuits.
 

growler

Senior Member
Location
Atlanta,GA
Hi all, first post here. I have been scouring the web this morning trying to find an answer to this question (a project is on hold over it). I cannot find any discussion about using 2-pole AFCI breakers in a 3 phase situation. I have a remodel with the small appliance circuits on a shared neutral. An alteration to the circuit means it now requires AFCI protection. The test button doesn't cause the breaker to trip (instantly failed inspection), and the contractor who installed it says it's because of the 3 phase application.
Any input?

Daniel

I'm not an expert in this as I have not tried an AFCI in a three phase panel.

But this doesn't sound right to me.

If you have 2 phases feeding 2 small appliance circuits with a shared neutral I can't see how the breaker could know the difference.

I would first see if the breaker is installed correctly and if it is I would try a different breaker.
Somehow the electronic test circuit in the breaker may have been damaged.

If you have a third phase sharing this neutral I would think the breaker would trip the minute you put a load on it.

Let us know how this works out because this is interesting and you may be the first to post this problem ( someone had to be first).
 
David, the small appliance circuits are on adjacent phases (A-B, B-C, C-A or something).
Growler, I agree on all counts. I haven't done it yet either, but the outgoing contractor did it in multiple panels and is now saying that the three phase configuration is the problem. Evidently, all 2-pole applications are having this issue, whereas the single pole application isn't. Short of having a Schneider engineer on hand, here I am.
I am about to get my lead and head down personally to put a finer point on this.

My strength does not yet lie in the residential work (commercial electrician in first year of contracting). I'll definitely post how this plays out. Thanks!
 

GoldDigger

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Location
Placerville, CA, USA
Occupation
Retired PV System Designer
The first thing to do is figure out whether the AFCI is tripping on the AF or GF protection function.
The probability is 99% that it is the ground fault protection.
What this is telling you is that the way the neutral for the multiwire branch circuit is wired some current in the circuit is returning to the service neutral through a path other than the MWBC neutral that is connected to the neutral terminal of the two-pole breaker.
(You did wire the neutral to the breaker, right? I have not seen a two-pole line-to-line only AFCI breaker, but if by some chance that is what you have, it will not work with an MWBC.)
The GF trip is most likely the result of cross connecting the circuit neutral somewhere to the neutral of another circuit. But it could also be a neutral touching the EGC or grounded metal in the box or raceway.

You should find that if you put in a two-pole GFCI breaker in place of the AFCI breaker it will trip too. That is the dead giveaway that tedious though it might be you need to troubleshoot each circuit to find where the wiring is incorrect.

That the test button fails to trip the breaker strongly suggests that you did not wire the neutral pigtail of the breaker to the panel neutral bus and so the control circuit in the breaker is not getting power.
 
The first thing to do is figure out whether the AFCI is tripping on the AF or GF protection function.
The probability is 99% that it is the ground fault protection.
What this is telling you is that the way the neutral for the multiwire branch circuit is wired some current in the circuit is returning to the service neutral through a path other than the MWBC neutral that is connected to the neutral terminal of the two-pole breaker.
(You did wire the neutral to the breaker, right? I have not seen a two-pole line-to-line only AFCI breaker, but if by some chance that is what you have, it will not work with an MWBC.)
The GF trip is most likely the result of cross connecting the circuit neutral somewhere to the neutral of another circuit. But it could also be a neutral touching the EGC or grounded metal in the box or raceway.

You should find that if you put in a two-pole GFCI breaker in place of the AFCI breaker it will trip too. That is the dead giveaway that tedious though it might be you need to troubleshoot each circuit to find where the wiring is incorrect.

That the test button fails to trip the breaker strongly suggests that you did not wire the neutral pigtail of the breaker to the panel neutral bus and so the control circuit in the breaker is not getting power.

The circuit does not appear to be tripping, just on inspection the test button failed to trip the breaker. I do not believe it is a dual function breaker, thus there is no integral GF protection. Neither my guys nor I wired the breakers; that was a different contractor. We are about to head down and more thoroughly investigate. In my short experience as a contractor, I am finding many reasons not to trust prior rehab work on multifamily residential jobs. I would not be surprised to learn that the neutral was not landed to the new breaker. Will update.
 

growler

Senior Member
Location
Atlanta,GA
Evidently, all 2-pole applications are having this issue, whereas the single pole application isn't. Short of having a Schneider engineer on hand, here I am.
I am about to get my lead and head down personally to put a finer point on this.


If a lot of these are not working I wonder if they could be designed to only use an operating voltage of 240V and not 208V.

It really doesn't make any sence because the thing would have to be able to detect an arc on either phase for it to be of any use and each phase is 120V to ground (neutral).


I think I would try to call schneider and see what they say. I have had good luck with their customer service.
 

GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
You mention that it is not a dual function AFCI/GFCI. That does not mean that there is not a GF trip in the AFCI breaker, just that it is not a Class A 6ma GF trip point.
These days some combo (not dual function) AFCIs still include a 30ma GF trip and others do not.
 

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
You mention that it is not a dual function AFCI/GFCI. That does not mean that there is not a GF trip in the AFCI breaker, just that it is not a Class A 6ma GF trip point.
These days some combo (not dual function) AFCIs still include a 30ma GF trip and others do not.

Square D, Siemens and Eaton CH still have GF protection. GE and Eaton BR no longer have GF protection.
 

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
I believe there was a post not long ago stating that Square D said their 2-pole GFCI breakers are not compatible with 208 Volt systems. If that is the case I could see having problems with 2 pole AFCI breakers. There are many dwellings fed by 208 volt systems so its pretty poor design if 2 pole AFCI's and GFCI's are not compatible. For new construction multi wire circuits can be avoided eliminating the need for 2 pole AFCI's. How are you supposed to GFCI protect a 208 volt load?
 

jumper

Senior Member
My little brain is having a hard time understanding how the breaker would notice/care/realize that it is in a three phase 208Y/120V panel vs a single phase 120/240 panel.

2 hots and a noodle = 2 hots and a noodle, no?
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
The only way the breaker could detect the difference is if:
1. The controls are powered line to line and 208V is too low (at the bottom limit for 208 service) for reliable operation, or
2. The circuitry is sensitive to the different phase angles. That could be related to signature analysis of either a parallel arc or a series arc.
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
The only way the breaker could detect the difference is if:
1. The controls are powered line to line and 208V is too low (at the bottom limit for 208 service) for reliable operation, or
2. The circuitry is sensitive to the different phase angles. That could be related to signature analysis of either a parallel arc or a series arc.

If it is true that they do not work on 208 you probably hit the nail on this one.
:thumbsup:
 
So. At long last I have time to reply. Evidently, the HOM type 20/2 AFCI breaker is not compatible with 208Y/120 systems. There's a big sticker right on the breaker that makes it very clear. The original contractor supposedly called Schneider to see if they make one, I didn't ever hear back on how that played out. My installation will avoid the need by running a dedicated circuit instead of relying on adding protection for a multiwire branch circuit.
As far as why the 20/2 AFCI isn't compatible with 208Y/120, the only thing I can come up with is how ground is referenced when dealing with 3 phases. That is, there are 2 phases both referencing ground in 3 phase in this situation, whereas in a single phase application, there's just the one phase. I won't pretend to understand the intricacies of AFCI protection, how it actually works, but this seems like a likely culprit.
 

kwired

Electron manager
Location
NE Nebraska
So. At long last I have time to reply. Evidently, the HOM type 20/2 AFCI breaker is not compatible with 208Y/120 systems. There's a big sticker right on the breaker that makes it very clear. The original contractor supposedly called Schneider to see if they make one, I didn't ever hear back on how that played out. My installation will avoid the need by running a dedicated circuit instead of relying on adding protection for a multiwire branch circuit.
As far as why the 20/2 AFCI isn't compatible with 208Y/120, the only thing I can come up with is how ground is referenced when dealing with 3 phases. That is, there are 2 phases both referencing ground in 3 phase in this situation, whereas in a single phase application, there's just the one phase. I won't pretend to understand the intricacies of AFCI protection, how it actually works, but this seems like a likely culprit.
I would think it has to do with the 120 degree phase angle between the two ungrounded conductors on a three phase system vs. 180 degree phase angle between them on a single phase system. No one seems to fully understand just what "signature" AFCI's are looking for in the first place and has been mentioned that not all of them are looking for the same signatures either - so it wouldn't surprise me that the different phase angle would cause troubles.

GFCI's are simpler - all they are looking for is net current going out vs net current returning - if nothing is returning via some unmonitored path - there is no unbalance to cause current in the CT and initiate the trip sequence. And AFAIK most 2 pole GFCI's still connect their "control circuit" from one line to neutral so the control circuit still sees 120 volts whether the source is 208/120 or 120/240.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
I noticed in the description of the 2-pole AFCI that it said 120V. The 2-pole GFCI says 240/120V. The 2-pole AFCI is specifically for MWBC since 240V or 208V circuits don't require AFCI.

However, I found a diagram of the breaker and it says 240V/120V but you can see the label on it that has a slash through 208V/120V, meaning "no" or "not for use" on 208V/120V.

Now since both legs referenced to neutral are 120V I don't understand why they wouldn't work on 208V. Unless the tripping/testing unit control is powered by both legs (240V) and 208V is too low.

Edit: I just noticed it also says single phase on it also.

efa0819c-79ce-4745-b238-82810798f99c.png._V333690310__SR970,300_.png
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
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Licensed Electrician
I noticed in the description of the 2-pole AFCI that it said 120V. The 2-pole GFCI says 240/120V. The 2-pole AFCI is specifically for MWBC since 240V or 208V circuits don't require AFCI.

However, I found a diagram of the breaker and it says 240V/120V but you can see the label on it that has a slash through 208V/120V, meaning "no" or "not for use" on 208V/120V.

Now since both legs referenced to neutral are 120V I don't understand why they wouldn't work on 208V. Unless the tripping/testing unit control is powered by both legs (240V) and 208V is too low.

Edit: I just noticed it also says single phase on it also.

efa0819c-79ce-4745-b238-82810798f99c.png._V333690310__SR970,300_.png
But AFCIs have been subjected to 50 different performance test. Our resident NEMA rep bphgravity http://forums.mikeholt.com/member.php?u=56637 said so .

Thank heaven above and all that is good in the world that AFCIs are out there to protect us from refrigerator LEDs and poor phase angles.
 

kwired

Electron manager
Location
NE Nebraska
But AFCIs have been subjected to 50 different performance test. Our resident NEMA rep bphgravity http://forums.mikeholt.com/member.php?u=56637 said so .

Thank heaven above and all that is good in the world that AFCIs are out there to protect us from refrigerator LEDs and poor phase angles.
I still am convinced it is the phase angle that is the problem, not because 120 degrees has anything wrong with it, just that the way the device works is apparently needs to see a 180 degree angle, anything different may be a condition requiring it to trip. These things apparently are supposed to analyze the current waveform and maybe even the voltage wave form, for no more then I do know about them I could see such a difference in phase angle easily causing troubles.

One can't really compare them to GFCI's on this issue as they don't function the same way at all other then the GFP portion of the AFCI's that still use that, but I don't see that as being a problem here.
 

growler

Senior Member
Location
Atlanta,GA
I cannot find any discussion about using 2-pole AFCI breakers in a 3 phase situation. I have a remodel with the small appliance circuits on a shared neutral. An alteration to the circuit means it now requires AFCI protection. The test button doesn't cause the breaker to trip (instantly failed inspection), and the contractor who installed it says it's because of the 3 phase application. l

David, the small appliance circuits are on adjacent phases (A-B, B-C, C-A or something).

So. At long last I have time to reply. Evidently, the HOM type 20/2 AFCI breaker is not compatible with 208Y/120 systems. There's a big sticker right on the breaker that makes it very clear.


There are still some questions. Not just for the OP but for anyone.

Is there a quare D homeline panel that's listed for 208Y-120V? I didn't even know that there was a homeline 3 phase panel. If you use a single phase wouldn't it be marked wrong?

Is it just the homeline version that can't be used with 208Y-120V or also the QO type?

If it is a phase angle problem on three phase will a single pole arc fault work correctly when installed in a three phase situation ? Do they make a breaker that will work on 208Y-120V?
 

kwired

Electron manager
Location
NE Nebraska
There are still some questions. Not just for the OP but for anyone.

Is there a quare D homeline panel that's listed for 208Y-120V? I didn't even know that there was a homeline 3 phase panel. If you use a single phase wouldn't it be marked wrong?

Is it just the homeline version that can't be used with 208Y-120V or also the QO type?

If it is a phase angle problem on three phase will a single pole arc fault work correctly when installed in a three phase situation ? Do they make a breaker that will work on 208Y-120V?
There is no three phase panels in the Homeline series, it is however common to see multi-tenant units that have a 208/120 source divided into 208/120 single phase three wire feeds to each tenant and use single phase panels in each tenant space. You still have the 120 degree phase angle between the two ungrounded conductors. Ungrounded to neutral (120 volt loads) will still see 180 degrees between the two circuit conductors as this is truly a single phase section of the supply system and is reason a single pole AFCI wouldn't see any difference no matter which system it is supplied by.

Homeline and QO both are rated for 240 maximum, which 208 falls within the range. Only exceptions would be things like an AFCI that may have issues like mentioned in this thread. Standard thermal magnetic breakers will work fine on 208 volts.

We use larger frame breakers rated for 600 volts all the time for 208, 240, and 480 volts applications, they don't care what the voltage is as long as we keep it under maximum rating.
 
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