# DP Arc Fault Breakers



## backstay (Feb 3, 2011)

Anyone wiring with DP arc faults? I just did a service call on a house where the previous EC ran 14/3 HRs and DP arc faults. I looked up the price and SP Siemens are $50 and DP are only $77. I may start doing this where it would save time and money.


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## Black Dog (Oct 16, 2011)

backstay said:


> Anyone wiring with DP arc faults? I just did a service call on a house where the previous EC ran 14/3 HRs and DP arc faults. I looked up the price and SP Siemens are $50 and DP are only $77. I may start doing this where it would save time and money.


I wonder how much trouble those will cause with splitting up loads like that, I believe the load must be balanced otherwise the neutral will pick up the imbalance and trip.


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## Black Dog (Oct 16, 2011)

Also:

Single pole murrays are $35 if you buy 10 or more at HD.


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## AK_sparky (Aug 13, 2013)

Black Dog said:


> I believe the load must be balanced otherwise the neutral will pick up the imbalance and trip.


I highly doubt that. It doesn't make sense that it would be designed like that. But I have been wrong before....


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## B-Nabs (Jun 4, 2014)

You can put mwbcs on dp arc fault breakers with no problem at all. Provided, of course, that there are no wiring issues like standing ground faults or over driven staples and the like, but that is true of the sp ones as well. the neutral of the mwbc goes on the breaker and the breaker has either a neutral tail or a plug on neutral, and as long as the math works out between all the conductors everything is copacetic.


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## MF Dagger (Dec 24, 2007)

I use 2 pole AFCI's all the time. Like you said per pole they are cheaper. Some spots I'm using dual functions instead so until they come out with a 2 pole dual function I run standard to those.


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## MTW (Aug 28, 2013)

Black Dog said:


> I wonder how much trouble those will cause with splitting up loads like that, I believe the load must be balanced otherwise the neutral will pick up the imbalance and trip.


:no:

The whole point of a double pole AFCI is so that it can be used with a shared neutral.


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## Southeast Power (Jan 18, 2009)

backstay said:


> Anyone wiring with DP arc faults? I just did a service call on a house where the previous EC ran 14/3 HRs and DP arc faults. I looked up the price and SP Siemens are $50 and DP are only $77. I may start doing this where it would save time and money.


That's such good news, I was wondering what we were going to have to do in on dear houses with MWBCs installed.


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## markbrandx (Oct 11, 2015)

I believe Gfi breakers are sensing current imbalance and a 2 pole breaker with a shared neutral would not work. Afci's are sensing a signature voltage waveform that is unique to arcing current. A 2 pole Afci breaker with a shared neutral should work.


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## oliquir (Jan 13, 2011)

markbrandx said:


> I believe Gfi breakers are sensing current imbalance and a 2 pole breaker with a shared neutral would not work. Afci's are sensing a signature voltage waveform that is unique to arcing current. A 2 pole Afci breaker with a shared neutral should work.


not true, a dp gfi will work on mwbc even if current is not the same in both legs. think of a spa that needs 120/240v, current isnt the same in both legs


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## markbrandx (Oct 11, 2015)

I stand corrected. They do make 120/240v rated dp gfi's. I had to do some looking into. They measure the neutral and both hot wires. This will work if the panel is fed from the very common single phase center tapped 240v transformer. Being all in phase the net sum is zero. I did not find a 120/208v rated dp gfi. Thanks oliquir


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## Gnome (Dec 25, 2013)

DP GFCIs work fine on 120/208. See this sheet from Eaton for example.


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## ELECTRICK2 (Feb 21, 2015)

markbrandx said:


> I stand corrected. They do make 120/240v rated dp gfi's. I had to do some looking into. They measure the neutral and both hot wires. This will work if the panel is fed from the very common single phase center tapped 240v transformer. Being all in phase the net sum is zero. I did not find a 120/208v rated dp gfi. Thanks oliquir


Shouldn't matter if it's a 3 phase 120/208 or single phase 120/240.
Think of it this way, if you have a 2P breaker feeding a split receptacle in an office building and you put your amprobe around both hots and the neutral you should read zero volts.
I say should read zero cuz some guys try to use the same neutral for another circuit. This won't work with a 2 pole GFI breaker


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## markbrandx (Oct 11, 2015)

I'm still not sure how the phase difference affects what the gfi's are sensing on a dp 120/208 application. The 24 ms trip time is more then 1 cycle 50 or 60 hz. I guess that's enough to get the job done. You have educated me gentlemen.


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## hardworkingstiff (Jan 22, 2007)

The only reason I can see to not use the DP AFCI breaker is that you lose 2 circuits if you have a problem. If it's in the wiring, the homeowner loses the non offending circuit until a sparky can find/fix the problem.

If I was the homeowner, I'd like the option of paying a few dollars more to not have the MWBCs in my home.


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## backstay (Feb 3, 2011)

hardworkingstiff said:


> The only reason I can see to not use the DP AFCI breaker is that you lose 2 circuits if you have a problem. If it's in the wiring, the homeowner loses the non offending circuit until a sparky can find/fix the problem.
> 
> If I was the homeowner, I'd like the option of paying a few dollars more to not have the MWBCs in my home.


I thought of that which is why I asked. Cutting the arcfault circuits into smaller runs is easier to trouble shoot. The place I was at had maybe four or five installed. On long HRs using 14/3 or 12/3 has other benefits.


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## hardworkingstiff (Jan 22, 2007)

backstay said:


> On long HRs using 14/3 or 12/3 has other benefits.


Other than voltage drop help (which of course depends on circuits of opposite phases having current), what other benefits are there (I was assuming you were talking about operations, so I guess cost of the home run savings can be added to the breaker cost savings)?


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## backstay (Feb 3, 2011)

hardworkingstiff said:


> Other than voltage drop help (which of course depends on circuits of opposite phases having current), what other benefits are there (I was assuming you were talking about operations, so I guess cost of the home run savings can be added to the breaker cost savings)?


Voltage drop and install costs.


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## Bird dog (Oct 27, 2015)

Also understand because of price you may do it one way on a job, but, if it were in your house you may do one step better.


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## backstay (Feb 3, 2011)

Bird dog said:


> Also understand because of price you may do it one way on a job, but, if it were in your house you may do one step better.


If it were my house, arcfaults would be going in.


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## Bird dog (Oct 27, 2015)

backstay said:


> If it were my house, arcfaults would be going in.


I would put in GFIs on all the 120v ckts and a GFI on the water heater. Also, at the water heater bond the hot and cold water together with a #6 and run it to the panel. I would skip the AFCIs if I could.


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## backstay (Feb 3, 2011)

Bird dog said:


> I would put in GFIs on all the 120v ckts and a GFI on the water heater. Also, at the water heater bond the hot and cold water together with a #6 and run it to the panel. I would skip the AFCIs if I could.


What about the range?


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## Bird dog (Oct 27, 2015)

backstay said:


> What about the range?


I suppose I could. I'm going by what i've seen and heard. I don't see a reason to do the range.


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## hardworkingstiff (Jan 22, 2007)

backstay said:


> If it were my house, arcfaults would be going in.


I guess that means you think they work and are a good addition?


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## backstay (Feb 3, 2011)

hardworkingstiff said:


> I guess that means you think they work and are a good addition?


Auto correction, should have said wouldn't. Maybe the breaker manufactures are changing posts to spin a positive on arcfaults!


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## markbrandx (Oct 11, 2015)

The gfi's have been proven to save lives. I still believe the code got carried away with all the locations requiring them. The afci's are to prevent fires? It's been several years since the code change. Has anyone seen any documentation proving their effectiveness?


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## hardworkingstiff (Jan 22, 2007)

markbrandx said:


> Has anyone seen any documentation proving their effectiveness?


I think that might be difficult to document. If the AFCI is working properly someone will fix the problem before it could come to a fire, but the question would be would that problem wind up causing a fire or just fail at a latter date (just to be fixed then).


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