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Thread: Two pole arc fault breakers for multi wire circuits

  1. #1
    DIY Senior Member Homeownerinburb's Avatar
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    Default Two pole arc fault breakers for multi wire circuits

    Arc fault breakers have earned a reputation for being finicky and trip happy, and all the while being difficult to troubleshoot. Possibly that is overblown. Hopefully, now that the technology is about a decade on the market, the manufacturers are coming to terms with the issues, assuming that they existed.

    What concerns me is the concept of using a two pole arc fault to protect an old three wire circuit. It just seems to me that as squirrelly as arc faults may be, using them in a three wire circuit is going to double my client's grief.

    http://w3.usa.siemens.com/powerdistr...pole-afci.aspx

    Has anyone got practical, recent experience of installing similar equipment to protect 60 year old three wire circuits?

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    Moderator & Master Plumber hj's Avatar
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    I assume by "three wire circuit" you mean a shared pair of 120v circuits with a common neutral, rather than a 3 wire 120/240v circuit. It would depend on how it senses the "arc fault" because if the two circuits are balanced, there is no flow through the neutral for it to compare against the flow in the 'hot lines"
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    DIY Senior Member Homeownerinburb's Avatar
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    Quote Originally Posted by hj View Post
    I assume by "three wire circuit" you mean a shared pair of 120v circuits with a common neutral, rather than a 3 wire 120/240v circuit. It would depend on how it senses the "arc fault" because if the two circuits are balanced, there is no flow through the neutral for it to compare against the flow in the 'hot lines"

    Yes. Thanks. No, I do not mean a stove or dryer or an air conditioner, which, btw, are not required to be protected by an arc fault breaker.

    Only branch circuits, and only some of them, are required to be protected by arc fault breakers.

    Branch circuits mean 12ov circuits. Three wire circuits do indeed mean a pair of 120v circuits at opposite potential, with a common neutral.

    So. If anyone else has actual experience in this, I'd be glad to hear from him or her.

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    DIY Senior Member houptee's Avatar
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    Just curious, if you are adding arc faults to an existing panel or is it a panel upgrade.
    In NJ on an existing home you do not have to install them, even with a panel upgrade, only on new construction in NJ do you have to meet all requirements of NEC 2011.
    We have a different code book called the NJ renovation sub-code for existing structures.
    Another example in NJ an existing 3 prong range or dryer outlet does not have to be updated to a new 4 prong type unless you are replacing the branch circuit wiring.
    Same for tamper resistant outlets, the old non TR ones can remain unless you replace them, then you have to put in TRs.

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    Moderator & Master Plumber hj's Avatar
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    quote; I do not mean a stove or dryer or an air conditioner, which, btw, are not required to be protected by an arc fault breaker.

    I have found it is always better to "define the terms" before advancing, because sometime a complex answer is given, and then the O.P. posts back that "that was not what I was referring to".

    quote; Branch circuits mean 12ov circuits

    My definition of a "branch circuit" is anything that is NOT a main circuit feeding a panel.
    Licensed residential and commercial plumber

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    Jack of all trades DonL's Avatar
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    Quote Originally Posted by Homeownerinburb View Post
    Arc fault breakers have earned a reputation for being finicky and trip happy, and all the while being difficult to troubleshoot. Possibly that is overblown. Hopefully, now that the technology is about a decade on the market, the manufacturers are coming to terms with the issues, assuming that they existed.

    What concerns me is the concept of using a two pole arc fault to protect an old three wire circuit. It just seems to me that as squirrelly as arc faults may be, using them in a three wire circuit is going to double my client's grief.

    http://w3.usa.siemens.com/powerdistr...pole-afci.aspx

    Has anyone got practical, recent experience of installing similar equipment to protect 60 year old three wire circuits?

    That should be a good breaker.

    Some of the first breakers were problems in normal installs. Hair dryers that have brushes are great Spark Gap generators for testing.

    Filtering and detecting a true Arc is better on the new breakers and small amounts of RFI will not trip them.


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    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by Homeownerinburb View Post

    Has anyone got practical, recent experience of installing similar equipment to protect 60 year old three wire circuits?
    No, since there would be no reason to do so.
    WHY are you adding AFCI to an old circuit?

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    DIY Senior Member Reach4's Avatar
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    Quote Originally Posted by Speedy Petey View Post
    No, since there would be no reason to do so.
    WHY are you adding AFCI to an old circuit?
    I am going to predict the answer is to prevent a fire.

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    Moderator & Master Plumber hj's Avatar
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    quote; I am going to predict the answer is to prevent a fire.

    In that case, maybe he should be upgrading the wiring system, instead of using a Bandaid on it.
    Licensed residential and commercial plumber

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    DIY Senior Member Vegas_sparky's Avatar
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    When AFI's first hit the street I looked into what their function was. Their most unique protection is against arcing from L-N. Preventing fires is their intended purpose. Small defects in appliance/fixture cords, a piece of Romex getting damaged from a picture hanging nail, or a lamp knocked over and having the glass of the lamp broken(but not the filament) are conditions where sparks could be generated, but a typical breaker or GFCI wouldn't sense the fault. Those are fire dangers that are pretty much always present in an occupied dwelling. The new breakers you posted about may lead to mandatory retrofit installations. The only good thing is that nuisance tripping is much less than it was when AFIs were first introduced 10+ years ago.

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    DIY Senior Member Homeownerinburb's Avatar
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    Quote Originally Posted by Speedy Petey View Post
    No, since there would be no reason to do so.
    WHY are you adding AFCI to an old circuit?
    I'm replacing the panel, and I am extending the existing circuits for lighting and ceiling fans.

    That would be the reason for doing so. Well, that and the authorities insist on it.

  12. #12
    DIY Senior Member Homeownerinburb's Avatar
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    Quote Originally Posted by hj View Post
    quote; I am going to predict the answer is to prevent a fire.

    In that case, maybe he should be upgrading the wiring system, instead of using a Bandaid on it.
    Local codes are what is driving the decision.

    The difficulty with upgrading the wiring: while it is in conduit, yes, the house is on a slab and there is no attic.

    Which means that the conduit passes under the slab. For the last 60 years.

    Not only am I loath to try to pull new conductors thru metal conduit that has been buried for 60 years, most or all the boxes in the house are the minimum that was permissible. The capacity of a classic handy box used for an outlet is pretty minimal. 14.5 cub inches. Two wires in, two wires out, one wire straight thru, count two more wires for the receptacle. That is seven wires. Assuming it is all 14 gauge, that is two inches each, for 14 inches, so, to go to two circuits each with a dedicated neutral means needing to tear out many boxes.

    The client is on a VERY tight budget. Seriously tight. Single mother school teacher tight.

    So if I can resolve some of the circuits with a two pole arc fault, that is obviously the correct path.

    One item to be happy about: I'll be replacing ALL the receptacles and switches, which means that EVERY wire splice in the unit will be very, very sound. I splice with serious intent.

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    DIY Senior Member Homeownerinburb's Avatar
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    Quote Originally Posted by hj View Post
    quote; I do not mean a stove or dryer or an air conditioner, which, btw, are not required to be protected by an arc fault breaker.

    I have found it is always better to "define the terms" before advancing, because sometime a complex answer is given, and then the O.P. posts back that "that was not what I was referring to".

    quote; Branch circuits mean 12ov circuits

    My definition of a "branch circuit" is anything that is NOT a main circuit feeding a panel.

    Fair enough. The fact remains, at least as best as I know, that arc faults are not required for small appliance outlets on the counter in the kitchen, not the fridge, not the range hood (which locally now must be a dedicated 20 amp in anticipation of the placement of a microwave/range hood) not the laundry, not the garbage disposal or dishwasher, and not the bathroom outlets which should be dedicated 20amp circuits. And certainly not any 240v circuits of any description.

    The client also wants a combination heater/vent/light in the bath ceiling. I expect to make that a 20 amp dedicated circuit, and hope to not need to protect it with a arc fault.

    I am hoping to install a twelve space 100 amp panel. The house is under 1100 sq ft, and no load calc indicates any need for more. Except you cannot find 100amp panels with more than 12 spaces, and the arc fault breakers are only available in 1" per pole, as opposed to conventional breakers, that can be had in 1/2".

    But I can wire this place up, and to code, with 12 spaces. Just.
    Last edited by Homeownerinburb; 01-09-2014 at 09:42 AM.

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    DIY Senior Member Vegas_sparky's Avatar
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    AFI are required by 2011 NEC(210.12) to protect circuits in locations just about anywhere a GFI isn't. There is an exception(#((A)(2)) that if your branch circuit is in conduit from your overcurrent device, with 2" concrete cover, that an AFI branch circuit device can be used to protect the remainder of the circuit.

    With your situation it may help with cost, and breaker space as recepticle circuits fed by 1/2" breakers can use the AFIs in the field at first device, and lighting/etc would have to have the dedicated full size AFI breakers. I can guarantee the AFI recepts will be cheaper than AFI breakers, and you're switching out all the trim anyways. Win, win.
    Last edited by Vegas_sparky; 01-09-2014 at 12:13 PM. Reason: specify exception

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    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by Homeownerinburb View Post
    I'm replacing the panel, and I am extending the existing circuits for lighting and ceiling fans.

    That would be the reason for doing so.
    IMO extending old circuits, ESPECIALLY multi-wire circuits, is a last resort. I'd run new for new things.
    Installing AFCI on old circuit is asking for trouble.


    Quote Originally Posted by Homeownerinburb View Post
    Well, that and the authorities insist on it.
    Is this something they have in writing, or are you just blindly doing what they want?
    It is NOT required to install AFCI's for a panel change unless there is some weird local amendment.

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