AFCI on MWBC

[Jarnipman]

Hi everyone,

I have been using GE's fancy single pole AFCI breakers tied together on MWBC for sometime now on upgrading existing MWBC. I’m confused on a couple of things here and thanks in advance for reading my rambling questions....

1. What kind of sorcery is occurring in the GE circuitry that does not require ground fault sensing in their fancy single pole AFCI breakers that can be tied on MWBC?

2. If GE states that the neutral can be connected to either breaker and the breaker only monitors the hot, why do you have to connect the neutral to the AFCI breaker anyway, since one will not have it connected no matter what, why not straight to the bus bar? - I wouldn’t do that, I would follow GE’s literature, just curious, is one breaker monitoring the neutral and sharing that information through the neutral to the circuit board on the adjacent tied breaker through the hot? I don’t know these breakers seem like black boxes to me.

3. Can GE’s DFCI breakers also be tied together on a MWBC with neutral landing on either one – I don’t think so, am I wrong? I can’t figure this out from their nebulous literature. I don’t see how this would work because GFCI needs to monitor for ground faults, but maybe they make a magic DFCI that does not need this?

4. Will GFCI outlets work downstream of two GE AFCIs tied together on MWBC, when one of the breakers will have the neutral landed on it and the other will not? Will GFCI outlets work on both breakers? Can the GFCI outlet on the circuit of the MWBC that has the neutral landed on the other breaker sense ground faults properly on that side of the MWBC?

5. Why can I not find a big box of DFCI outlets to purchase that I can use for upgrading existing circuits in irritating areas that require both GFCI/AFCI – on many of these existing installs there is no space in the panel for this nonsense.

6. Why is electrical equipment so expensive, figure a DFCI, GFCI, CAFCI whatever breakers costs what it does, when the Chinese can make a blue ray player for less than the cost of a breaker, why the heck doesn’t someone make aftermarket breakers for $5 and get them UL listed for all vendors? I men really, if you can make a blue ray player and sell it for $50 at Costco, why can't someone make these breakers for even $2? There seems like big monopolies and very limited aftermarket competition in the electrical business say vs. the auto parts industry and it's not like electrical is a small niche market, it's everywhere!

Thanks for reading my long winded post and sorry for making it so long with so many questions, but I have to unload my building up of questions….

 

[Dennis Alwon]

For those who are not familiar here is the afci diagram for ge afci's used on a multiwire branch circuit. As you can see the load neutral only needs to go to one breaker

 

[GoldDigger]

Note that you must still connect the neutral pigtails on both breakers, since they are necessary to power the electronics.

 

[Jarnipman]

Thanks guys for posting the diagram and the pigtail reminder in reference to my post, what I was hoping to see from GE is the exact same diagram for their DFCI on MWBC, but that does not exist does it?

 

[Jarnipman]

Not to hijack my own thread on something unrelated, but it's kind of related because we are discussing CAFCI breakers, etc.....but on other systems that use a plug on neutral breaker (Square D as an example), does the plug on neutral connection ever get loose with time vs the pigtail connection under a screw terminal on the bar? Been wondering about this, the plug ons sure do make your panel look spiffy vs those hideous curly cues all over the place. But my concern is that plug on neutrals might end up like all the backstabbed device connections 10 years from now that I am constantly moving under the screw terminals after wires get loose and either not function or even worse arc.

 

[Dennis Alwon]

I can't imagine you can use this setup on a DFCI. It would have GFCI in it whereas the afci does not

 

[GoldDigger]

Thanks guys for posting the diagram and the pigtail reminder in reference to my post, what I was hoping to see from GE is the exact same diagram for their DFCI on MWBC, but that does not exist does it?

No it does not, since the GFCI function must compare the neutral current to the vector sum of the two or three ( three phase) line currents.
The two single pole breakers cannot share the needed information (unless they have a hypothetical two wire interconnect to allow CT output current to be summed across the two breakers).

 

[Jarnipman]

That's what I was wondering, it makes sense that it wouldn't work for GFCI for your stated reasons, but was not sure if the GE electrical engineers did not come up with some way to communicate a signal between the two breakers through the neutral pig tails or hot that accounted for these things and process the signal in some fancy way, kind of like the way you can run broadband over power lines, if you can watch netflix movies which basically move through your breakers, they should be able to figure out how to make the DFCI work on MWBC - I don't know I'm not an electrical engineer so that is way over my head, I just do what the manufacturer says and what I have been trained to do.

 

[GoldDigger]

Think about what would be involved: either an analog signal or a digital signal so accurate that it would be within 1ma out of 20A. Not likely.

 

[Jarnipman]

Ya your right, that's to much work to satisfy a need that can be figured out with much more cost effective measures. Placerville is a super cool place - I grew up mining in Mariposa County nearby and really miss it.

 

[donaldelectrician]

I can't imagine you can use this setup on a DFCI. It would have GFCI in it whereas the afci does not

Dennis -

What is a , " DFCI " , ?

Got me there .


Don

 

[GoldDigger]

Dennis -

What is a , " DFCI " , ?

Got me there .


Don

Dual Function Circuit Interrupter = combined GFCI and AFCI.

 

[al hildenbrand]

1. What kind of sorcery is occurring in the GE circuitry that does not require ground fault sensing in their fancy single pole AFCI breakers that can be tied on MWBC?

Simply, the circuitry and programming in the single pole GE AFCI, from "MOD 3" onward, have been purely arc fault sensing. GE's R&D people accomplished that without the need to include "ground fault sensing circuitry" to cover all the bases.

2. If GE states that the neutral can be connected to either breaker and the breaker only monitors the hot, why do you have to connect the neutral to the AFCI breaker anyway, since one will not have it connected no matter what, why not straight to the bus bar? - I wouldn’t do that, I would follow GE’s literature, just curious, is one breaker monitoring the neutral and sharing that information through the neutral to the circuit board on the adjacent tied breaker through the hot? I don’t know these breakers seem like black boxes to me.

The single pole GE AFCI gets all the information it needs to do its job as an AFCI from the current and voltage on the hot conductor. It doesn't need any information from the neutral.

3. Can GE’s DFCI breakers also be tied together on a MWBC with neutral landing on either one – I don’t think so, am I wrong? I can’t figure this out from their nebulous literature. I don’t see how this would work because GFCI needs to monitor for ground faults, but maybe they make a magic DFCI that does not need this?

You are not wrong. The Dual Function Circuit Interrupter (DFCI) is both an AFCI and a Class A GFCI in one single breaker body. A Class A GFCI must have its downstream neutral isolated to the downstream hot from the LOAD side of the GFCI only, and it can't have leaks to ground. . . just like any GFCI device you've installed before.

4. Will GFCI outlets work downstream of two GE AFCIs tied together on MWBC, when one of the breakers will have the neutral landed on it and the other will not? Will GFCI outlets work on both breakers? Can the GFCI outlet on the circuit of the MWBC that has the neutral landed on the other breaker sense ground faults properly on that side of the MWBC?

In a single word, "Yes." A downstream GFCI receptacle device cannot "see" how the upstream neutral is connected to the panel grounded service conductor, only that it IS connected. If any single downstream GFCI receptacle has a LOAD side connection, the LOAD side neutral can no longer be part of a multiwire branch circuit . . . just like any single pole GFCI you've hooked up before.

5. Why can I not find a big box of DFCI outlets to purchase that I can use for upgrading existing circuits in irritating areas that require both GFCI/AFCI – on many of these existing installs there is no space in the panel for this nonsense.

I wish they were available. Certain situations in existing dwelling wiring systems would greatly benefit from their existence. To my knowledge, no manufacturer of the OBC AFCIs (Outlet Branch Circuit AFCI) have released any for sale to us, yet. And I have not heard of any manufacturer that is working on one, as of this writing.

6. Why is electrical equipment so expensive, figure a DFCI, GFCI, CAFCI whatever breakers costs what it does, when the Chinese can make a blue ray player for less than the cost of a breaker, why the heck doesn’t someone make aftermarket breakers for $5 and get them UL listed for all vendors? I men really, if you can make a blue ray player and sell it for $50 at Costco, why can't someone make these breakers for even $2? There seems like big monopolies and very limited aftermarket competition in the business say vs. the auto parts industry and it's not like electrical is a small niche market, it's everywhere!

Pretty amazing. . . I agree. Had a customer that wanted a upgrade from 100 Amp fuse center to a 200 Amp circuit breaker center with no new circuits or location change. He had the notion that All AFCI would give him a break on his insurance, so he balked when he learned that the breakers needed (all GE single poles) would add $900 over the cost of the standard breaker. So he actually checked with his insurance company and they said they didn't care and wouldn't give him any discount. No AFCIs on that job.

 

[Jarnipman]

Thanks Al that is very helpful. I find it very amazing myself that insurance companies do not offer some sort of break for people that upgrade to AFCI or other current code standards voluntarily that might reduce fire/safety risk and you are right a lot of people don't want to pay for it, it is shocking to people when a panel is $100 and the breakers are a $1000. I am sure they have an actuary internally who has done the math, and they probably figure it would cost more to give people discounts on upgrades than it would to pay out total fire losses that might have been preventable when they happen. I think they should give everyone discounts. I like the technology, I put AFCI in my personal shop voluntarily along with GFCI of course and the AHJ asked me if I read NEC lately because AFCI was not required in my shop, but I told him it's my shop and I wanted the extra safety margin and besides I am sure it will be required in garages sooner or later so 10 years from now when i decide I need a new outlet, I will have AFCI already there. I have all the power tools, motors, etc you can think of, some cheap chinese tools, and I have never once tripped an AFCI in my shop or in my house where I also put them. The only time I have ever personally tripped a DFCI breaker interestingly enough was when I was painting a room in my house with water based paint and the paintbrush hit the terminals on an outlet (stupid me, but I was glad I had the DFCI there).

 

[Gene B]

The single pole GE AFCI gets all the information it needs to do its job as an AFCI from the current and voltage on the hot conductor. It doesn't need any information from the neutral.

But they still tell you to connect the neutral (to only one of the breakers). Is it a placebo?

I wish they were available. Certain situations in existing dwelling wiring systems would greatly benefit from their existence. To my knowledge, no manufacturer of the OBC AFCIs (Outlet Branch Circuit AFCI) have released any for sale to us, yet. And I have not heard of any manufacturer that is working on one, as of this writing.

Just announced, I don't know if you can actually buy it yet:
SmartlockPro Dual Function AFCI/GFCI Receptacle
http://www.leviton.com/OA_HTML/SectionDisplay.jsp?section=76642&minisite=10251

 

[Jarnipman]

No way, I knew Levitron would make one sooner or later, you should post this on the forum as a separate post so everyone knows about it. I googled it and this is the only supplier that came up from the model number (other than Levitron's website) - of course it's Home Depot that is the only website that came up on my search, but it looks like $30 retail. Does Viking carry it yet?

[url]http://www.homedepot.com/p/Leviton-SmartlockPro-15-Amp-12-Volt-Dual-Function-Circuit-Interrupter-DFCI-Receptacle-with-LED-Indicator-White-R02-AGTR1-0KW/206804820 [/URL]

 

[al hildenbrand]

But they still tell you to connect the neutral (to only one of the breakers). Is it a placebo?

Its real hard to know without any tech specs of the circuitry and programming. A third possibility is that the neutral landing on the LOAD side is an artifact of the NRTL standard and testing.

Just announced, I don't know if you can actually buy it yet:
SmartlockPro Dual Function AFCI/GFCI Receptacle
http://www.leviton.com/OA_HTML/SectionDisplay.jsp?section=76642&minisite=10251

Yay!!!! As I wrote the response above, I was hoping someone else would have news. Thanks, Gene.

The local Graybar anticipates product on their shelves in "a few weeks."

Jarnipman, as for Viking in the Metro, I don't think they stock much, if any, Leviton.