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GFCI operation question

Discussion in 'Electrical Engineering' started by Methos, Aug 25, 2006.

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  1. Bud--

    Bud-- Guest

    But all AFCIs include a 30mA GFCI as part of the protection. (That is
    not the same as a 6mA GFCI for shock protection of people.)
    Just to be clear, lighting circuits that include bedrooms have to be on
    an AFCI. (I think that is what you said.)

    bud--
     
  2. Guest

    | wrote:
    |>
    |> | Arc Fault Circuit Interrupter. The AFCI breakers look like, and wire
    |> | like GFCIs. AFCIs trip on arcs. The NEC requires them on new circuits to
    |> | bedrooms. The proposed 2008 NEC requires them for all residential 15 and
    |> | 20A circuits IIRC (could still be changed though).
    |>
    |> And AFCI-only device could be made to work without accessing the neutral
    |> of the circuit involved. The issue is the AFCI device needs to use power
    |> to function. Possibly that is the only purpose of the neutral pigtail if
    |> the device does not include any GFCI function.
    |>
    |
    | But all AFCIs include a 30mA GFCI as part of the protection. (That is
    | not the same as a 6mA GFCI for shock protection of people.)

    I've seen some that don't. Those were from Cutler-Hammer, the company
    that makes AFCI without GFCI, AFCI with 30maGFCI, and AFCI with 6maGFCI.

    If the NEC ends up requiring the GFCI function, then the ones without
    GFCI would likely end up being no longer made. But right not it is not
    clear what the NEC requires NOW (2005 code) or will require (2008 code).
    All we know is that the scope of where AFCI is required appears to be
    expanding.


    |> And regarding the issue of putting smoke detectors on AFCI protected
    |> circuits. The simple solution is keep receptacle circuits and lighting
    |> circuits separate, and put the smoke detectors on the lighting circuits.
    |> Those circuits should have much less instance of nuisance trips, and
    |> would more readily be noticed if they are opened, in case the smoke
    |> detector false to alarm.
    |>
    |
    | Just to be clear, lighting circuits that include bedrooms have to be on
    | an AFCI. (I think that is what you said.)

    All the circuits supplying outlets in the bedrooms must be AFCI protected.

    The issue with smoke detectors is more complex. I do believe they must
    be on AFCI, and I think that is appropriate. I do not expect the smoke
    detectors to be any source of nuisance trips. Thus it might seem to be
    a good plan to put them all on their own circuit. But I don't trust that
    they will alarm when the power is lost. The reason is because that would
    cause problems in utility outages. Do you want all your smoke detectors
    beeping when a storm knocks out your power? But what if the branch circuit
    the smoke detectors are on loses power. You might not even notice that a
    problem exists. Connecting smoke detectors with receptacles is a bad idea
    becauseof two reasons. Either the receptacle might not even get used, or
    the receptacle's usage might be the source of excess nuisance trips. That
    could compromise the safety of the smoke detectors. My idea is to put
    them on the same circuit as regularly used overhead lights, such as hall
    lights or stairway lights. That way, if there is a circuit trip that does
    affect the smoke detectors, you will be alerted to a problem with that
    breaker, and motivated to correct it.
     
  3. Guest


    It is the 21st century, why niot just have a dedicated alarm system in
    all houses that include smoke, pool and whatever with none of those
    fking 9v batteries?

    You do understand in a house with a 21' ceiling the smoke "shall" have
    a battery and it will be 21' off the floor. (maybe higher if it is in
    a tray) When the battery dies some people will shoot at it until it
    stops beeping. (whack with a broom or whatever)
    My wife carried the duty pager for 1000 closed houses for 2 weeks a
    while ago.
    She got 2 calls, Disconnect the pool alarm that won't stop beeping and
    get rid of that smoke detector we can't reach.
    The government is out of control.
     
  4. Bud--

    Bud-- Guest

    Have a reference handy for AFCIs without 30mA ground fault detection?

    (There was a proposal for the 2008 NEC to require that but it was rejected.)
    Do they chirp if the battery is dead? Removed? I havn't played with them.

    The way I understand the 2008 NEC-ROP, NFPA 760 requires smoke detectors
    that are on AFCI circuits have a secondary power source (battery).
    Another hidden requirement.

    IMHO requiring smoke detectors to be on an AFCI circuit lowers overall
    fire safety and is dumb.

    bud--
     
  5. Guest

    | Have a reference handy for AFCIs without 30mA ground fault detection?

    Some have 5ma GFCI and some have no GFCI:

    Page 22:
    http://www.eatonelectrical.com/unsecure/cms1/TB00300001E.PDF

    Pages 3 and 4:
    http://www.eatonelectrical.com/unsecure/cms1/TD00308001E.PDF

    Page 1:
    http://www.eatonelectrical.com/unsecure/cms1/TD01201036E.PDF


    | The way I understand the 2008 NEC-ROP, NFPA 760 requires smoke detectors
    | that are on AFCI circuits have a secondary power source (battery).
    | Another hidden requirement.
    |
    | IMHO requiring smoke detectors to be on an AFCI circuit lowers overall
    | fire safety and is dumb.

    I'm not convinced of that, yet.
     
  6. PPS

    PPS Guest

    Those without GFCI protection are intended for use in habitable and
    non-habitable spaces not requiring ground fault protection (living rooms and
    the like.)

    Those with 5ma GFCI protection are intended to serve bathrooms, kitchens and
    anywhere where a standard GFCI is required.

    Those with 30ma GFCI is designed to serve residential equipment noted in the
    NEC requiring 30 ma GFCI (actually termed GFEP to differentiate between the
    two.) Article 426.28 only requires ground fault protection for equipment, no
    personnel and that's to only place it can be used to meet code. To protect
    personnel, you must use 5ma protection.
     
  7. Guest

    | Those without GFCI protection are intended for use in habitable and
    | non-habitable spaces not requiring ground fault protection (living rooms and
    | the like.)
    |
    | Those with 5ma GFCI protection are intended to serve bathrooms, kitchens and
    | anywhere where a standard GFCI is required.
    |
    | Those with 30ma GFCI is designed to serve residential equipment noted in the
    | NEC requiring 30 ma GFCI (actually termed GFEP to differentiate between the
    | two.) Article 426.28 only requires ground fault protection for equipment, no
    | personnel and that's to only place it can be used to meet code. To protect
    | personnel, you must use 5ma protection.

    This is along the lines of what I expected, and certainly sounds very
    reasonable. Still, the required ground fault protection can be had with
    an AFCI that has no GFCI, or only has 30ma GFCI, as long as the 5ma GFCI
    receptacles are also used, where the GFCI people protection is required.
    Whether one would want to do it that way is another matter.

    In a bathroom, there is an advantage to having the ability to reset the
    GFCI device right there. That advantage may or may not be relevant for
    a kitchen. Other areas like a garage are probably not much of a concern.

    I have been told, but have never sacrificed a device to verify, or set up
    the appropriate test, that GFCI receptacles open BOTH the hot wire AND the
    neutral wire when they trip. If so, why is that? Is it to offer at least
    some protection even when the device is miswired? Or is there even some
    risk with voltages on the neutral wire?

    I do believe some neutral wire risk exists. It's certainly not as much as
    for the hot wire, usually in terms of voltage, and in terms of exposure
    events. One example of when the risk is high is when there is a open in
    in the supply neutral. But the chance of that happening coincident with
    contacting the neutral to ground, is much lower than either alone. The
    other risk is the voltage present as a function of the voltage drop along
    the supply neutral from the point of bonding to the point of contact.
    That's generally a very low voltage, though it can vary with loading on
    the system. Still, I'd feel safer having an interruption mechanism that
    will open BOTH wires together when tripped.

    Suppose you have an AFCI that includes GFCI protection, either at the 5ma
    level or the 30ma level, followed by a GFCI receptacle. Leakage from the
    neutral to ground would still result in a trip. But can it be guaranteed
    that the receptacle device will always open? Perhaps the breaker will open
    first, and de-energize the circuit before the receptacle can open, leaving
    the neutral wire still connected. To be assured that the receptacle will
    trip, I'd have to have no GFCI in the breaker, and place the GFCI protection
    in the receptacle, assuming it is designed to open the neutral.

    If I am forced to put GFCI protection in the breaker along with the AFCI
    protection, or if GFCI receptacles don't actually have neutral contacts
    that can be opened, I do have a fallback plan. I would run the circuit
    through a secondary box containing a 2-pole normally open electrically
    closed contactor. The circuit would run through these contacts. The
    coil would be powered from the supply side. If the breaker opens the
    hot wire, the coil will de-energize and open both wires. It won't be as
    quick an open since such contactors aren't listed for GFCI protection.
    But at least it will be something that can prevent certain problems.
    For shared neutral circuits, this would be a 3-pole contactor with a 240
    volt coil. These are avalable from Square-D and Cutler-Hammer. One issue
    that some people might be concerned with is the constant power used by the
    coil, 24x365xN.
     
  8. Bud--

    Bud-- Guest

    30mA ground fault detection in an AFCI is for arc protection. Far as I
    know all AFCIs include it (though I need to look harder at phil's 2nd
    link). Arcs can produce carbon paths which, if a ground is available,
    can produce ground fault currents. That may produce a trip before there
    is an arc or before an arc is detected.

    In the Consumer Product Safety Commission paper at:
    http://www.cpsc.gov/volstd/afci/AFCIFireTechnology.pdf
    that is explained on pdf page 14.

    Phil has a link in another thread to:
    http://www.eatonelectrical.com/unsecure/cms1/AFCI_UL_SPECIAL_SERVICES_INVESTIGATION.PDF
    which is a UL investigation showing that a "glowing connection" at a
    receptacle binding screw may (or may not) cause an AFCI trip through
    the 30mA ground fault function.


    I have read in newsgroups (so it must be true) that both poles are
    opened for hot-neutral-reverse protection.

    GFCIs (5mA) are now required to not work with reverse load-line terminal
    wiring. (Previously the load terminals connected to the receptacle.) I
    don't think you can do that without double pole contacts line-receptacle
    and line-load. And I don't think it can be done without that being a NO
    contact that requires the device to be powered to connect (which it
    wouldn't be if the line-side neutral was open).

    In both cases testing can be easily done without a hammer but so far I
    have been too lazy.

    bud--
     
  9. PPS

    PPS Guest

  10. Mark Lloyd

    Mark Lloyd Guest

    [snip]
    Even when that's exactly what you want.
    [snip]
    --
    87 days until the winter solstice celebration

    Mark Lloyd
    http://notstupid.laughingsquid.com

    "The government of the United States is not, in
    any sense, founded on the Christian religion."
    -- George Washington
     
  11. PPS

    PPS Guest

    Just opens the ungrounded conductor, not the ground (mistakenly called a
    neutral). It uses a special transformer to measure the current on the
    grounded and ungounded lines, and if they are not the same (within 5ma) it
    trips; assums that the lost current is leaking to ground somewhere (possibly
    through a person).
    Although the grounded conductor carries the same current as the ungrounded
    (white or identified) conductor (a white wire is only a neutral in a 120/240
    volt circuit, and carrys the unblanced load of the 120/240 volt applaince),
    it's at the same potential as you are. Both are grounded to the earth and
    (hopefully) there is no potential difference when a person contacts the
    white wire; threrefor no shock hazzard (under normal conditions, IE wired
    properly in the first place.)
     
  12. Guest

  13. Guest

    |
    |> I have been told, but have never sacrificed a device to verify, or set up
    |> the appropriate test, that GFCI receptacles open BOTH the hot wire AND the
    |> neutral wire when they trip. If so, why is that? Is it to offer at least
    |> some protection even when the device is miswired? Or is there even some
    |> risk with voltages on the neutral wire?
    |
    | Just opens the ungrounded conductor, not the ground (mistakenly called a
    | neutral). It uses a special transformer to measure the current on the
    | grounded and ungounded lines, and if they are not the same (within 5ma) it
    | trips; assums that the lost current is leaking to ground somewhere (possibly
    | through a person).

    So you are the first to contradict the others and say this?

    I know how they work. The issue is whether the groundED conductor, commonly
    known as the neutral, is opened as well.


    |> I do believe some neutral wire risk exists. It's certainly not as much as
    |
    | Although the grounded conductor carries the same current as the ungrounded
    | (white or identified) conductor (a white wire is only a neutral in a 120/240
    | volt circuit, and carrys the unblanced load of the 120/240 volt applaince),
    | it's at the same potential as you are. Both are grounded to the earth and
    | (hopefully) there is no potential difference when a person contacts the
    | white wire; threrefor no shock hazzard (under normal conditions, IE wired
    | properly in the first place.)

    Not quite true. The neutral (I don't know why you are caling it ungrounded)
    is NOT at exactly the same potential as ground. If it were, we'd have never
    had to have a separate groundING/EGC wire. The fact is, the neutral CAN be
    at potentials above the earth for various reasons. In most cases it will
    be just a few volts or a fraction of a volt due to voltage drop. In fault
    cases, it can be more serious. In open neutral cases it can be very serious.
     
  14. Bud--

    Bud-- Guest

    When the supply wires are connected to the LOAD terminals on old GFCIs,
    the GFCI receptacle is not protected - it is live even if the GFCI is
    tripped. (I believe the downstream circuit, which would be connected to
    the LINE terminals, is protected.)

    Under the new UL standard, which I think was adopted about 2 years ago,
    if you connect supply wires to the LOAD terminals the GFCI receptacle
    and LOAD terminals will always be dead.

    I may have tried to say that with too few words.

    bud--
     
  15. Guest

    | Mark Lloyd wrote:
    |> On Fri, 29 Sep 2006 11:00:11 -0500, Bud-- <>
    |> wrote:
    |>
    |> [snip]
    |>
    |>
    |>>GFCIs (5mA) are now required to not work with reverse load-line terminal
    |>>wiring.
    |>
    |>
    |> Even when that's exactly what you want.
    |>
    |
    | When the supply wires are connected to the LOAD terminals on old GFCIs,
    | the GFCI receptacle is not protected - it is live even if the GFCI is
    | tripped. (I believe the downstream circuit, which would be connected to
    | the LINE terminals, is protected.)
    |
    | Under the new UL standard, which I think was adopted about 2 years ago,
    | if you connect supply wires to the LOAD terminals the GFCI receptacle
    | and LOAD terminals will always be dead.
    |
    | I may have tried to say that with too few words.

    Someone once told me that the GFCI receptacles that I found were DANGEROUSLY
    susceptible to strong radio fields, must have been wired in reverse. But I
    do know they did cut off the power to its own outlets, so I am convinced
    that they were wired correctly. Maybe they are defective products and the
    internal solenoid that trips the mechanism was wired on the LINE side and
    should have been wired on the LOAD side.

    What happens is that when a strong radio field is introduced, the GFCI sees
    this somehow as leakage current. Other than for it being the wrong frequency
    this is understandable, as the induced currents would be in common mode, with
    the same direction on hot and neutral.

    The DANGEROUS part is that even though the solenoid has opened the circuit
    and cut off the power from the outlets (and presumably upstream, which was
    not present for the ones I did this with), as long as the radio current was
    present, the solenoid continued to activate. I believe that these solenoids
    would be operating from the 120 volts AND are not designed for the heat that
    would result from continuous operation. They would have been designed with
    the idea in mind that as soon as the circuit opened, the leakage current
    would no longer be present.

    This creates TWO hazard conditions.

    The first is that if a radio field that caused this was external, it might
    not be known to the radio operator that there was a problem. It could cause
    the solenoid to overheat, melt insulation, short circuit, arc, catch fire,
    burn the house down, and KILL PEOPLE. I did NOT leave the radio field on
    for a long period of time when I did this test. Even for the very first
    time I discovered this, the loud buzzing of the solenoid in the GFCI was
    loud enough to get my quick attention and realize the radio was triggering
    the problem. So I was never doing this for more than a second or two.

    The second hazard exists if the GFCI breaker does NOT open the neutral.
    A neutral could have some low voltages present as a result of voltage drop
    between various L-N 120 volt loads and the point of bonding neutral to
    ground. A short circuit from neutral to ground might not have a great
    spectacular arc flash, but it could draw enough current to activate a GFCI
    at the 5ma level. The type of GFCI that allowed the radio current to trip
    the solenoid continuously would also result in continuous activation of the
    solenoid in this neutral-only leakage situation because the neutral would
    not be opened, and the GFCI control circuitry would still be powered.

    I believe a proper GFCI design must cut off its own power when tripped, so
    it is not doing a continuous trip. This could be done by powering the GFCI
    control circuitry, including the solenoid, from the LOAD side. When I
    suggested this in a posting somewhere a long time ago, someone said that
    it may be needed to power the solenoid from the LINE side to ensure that
    it completes its operation to full open the contacts. I can agree that
    leaving the contacts stuck in a partial open state where they may arc
    across is not a good thing. But this should be accomplished through the
    mechanical energy stored in the unfatiguable spring mechanism that gets
    charged when the unit is reset. The solenoid should just be releasing
    that spring.

    DO NOT DO THIS AT HOME OR WORK. There is the risk that some of these units
    may be so defective that even a short period of operation could result in
    substantial damage.

    I also do not know if GFCI breakers have this risk. If their internal
    circuitry remains energized from the bus contacts in the panel, a radio
    field could cause the very same problem. Although they clearly do have
    the proper spring loading mechanism, being a part of a circuit breaker,
    the solenoid that releases that mechanism when leakage current is detected
    would potentially be under continuous operation if the power remains and
    the apparent leakage issue remains. This would not only be a problem
    with a continuous radio field, but it could also be a problem when the
    neutral has enough voltage to make a leak to ground, such as in a subpanel.
    So DO NOT DO THIS NEAR A BREAKER PANEL.
     
  16. ehsjr

    ehsjr Guest


    The grounding conductor is irrelevant to GFCI operation.
    Both the neutral and the hot are interrupted when
    a GFCI receptacle trips.


    It uses a special transformer to measure the current on the
    You have the above mis-identified. The neutral *is*
    the groundED conductor. The UNgrounded conductor is
    (a.k.a. "hot") NOT the white conductor, unless the
    circuit is miswired. The white can be re-identified
    as black with black tape or equivalent and then used
    as a hot wire.

    The difference is that the neutral (groundED) wire carries
    current, under normal circumstances. The groundING wire
    does not. It takes two faults to shock/hurt/kill you if
    you are in contact with the grounding wire; it takes one
    fault to shock/hurt/kill you if you are in contact with
    the neutral wire.

    Ed
     
  17. Guest

    | PPS wrote:
    |>>I have been told, but have never sacrificed a device to verify, or set up
    |>>the appropriate test, that GFCI receptacles open BOTH the hot wire AND the
    |>>neutral wire when they trip. If so, why is that? Is it to offer at least
    |>>some protection even when the device is miswired? Or is there even some
    |>>risk with voltages on the neutral wire?
    |>
    |>
    |> Just opens the ungrounded conductor, not the ground (mistakenly called a
    |> neutral).
    |
    |
    | The grounding conductor is irrelevant to GFCI operation.
    | Both the neutral and the hot are interrupted when
    | a GFCI receptacle trips.

    So why is the neutral opened? That's an "academic question" (I can come up
    with what I think are good reasons to do so). Now, considering answers to
    this question, what protections might be lost if AFCI breakers that include
    GFCI protection at the 5ma level result in GFCI receptacles not being used?
    Is GFCI protection in a breaker considered adequate for the requirements in
    NEC 210.8 even though it does not open the neutral connection? Would YOU
    persoanlly feel less safe if all the receptacles in a kitchen were protected
    for ground fault leakage only by circuit breakers at the panel (assume that
    the panel is close by).

    There must be _some_ reason _they_ chose to include opening the neutral in
    GFCI receptacles (maybe more than one). But wouldn't such reasons also be
    applicable to circuit breaker based protection?

    What if you have _both_ GFCI protection at the breaker _and_ GFCI protection
    at the receptacle, say in a bathroom. Now suppose there is a slight leakage
    fault, but only the breaker opens on it. Maybe the receptacle was going to
    interrupt the fault, but was just sufficiently slow, perhaps due to a slow
    rise in the leakage current, that the breaker did it first, which prevents
    the receptacle from doing so. Now you have a condition where the neutral
    continues to be fully connected all the way from the main panel, through
    the GFCI receptacle that no longer has power on it's hot wire, and into the
    plugged in appliance that someone grabbed with a dripping wet hand while
    also grabbing a towel out of the basin water in the sink.

    Well, usually, a neutral doesn't have much voltage relative to ground. But
    if there was some kind of open neutral condition also present (now we are at
    the level of _two_ existant problems) and a rather unbalanced load between
    the two single phase poles (somewhat common), we could be dealing quite many
    volts still available through the GFCI receptacle that didn't trip because
    it lost power due to the ground fault that was detected by the breaker first.

    So my thinking here is, if there is protection to be gained by opening the
    neutral at GFCI receptacles, we should _not_ be requiring that AFCI breakers
    be of the type that combine GFCI protection. And perhaps such breakers
    should be prohibited for these circuits.

    Of course there is also the issue of the inconvenience of going all the way
    to the breaker panel to reset a ground fault. This could be particularly
    so for bathrooms (imagine being dripping wet, wearing only a towel, going
    out to the garage or down to the basement, standing on a concrete floor,
    to reset a breaker).
     
  18. Guest

    In receptacle devices they open both sides because this may be used to
    extend older wiring where there may be a polarity reversal. In K&T
    polarity was far from a priority and you pretty much have a 50:50
    chance on which wire is hot. With no other ground reference handy it
    is hard for a contemporary installer to figure it out
     
  19. What makes you so certain that a GFCI circuit breaker does not open the
    neutral? Have you checked with several manufacturers.

    One reason why it might be OK for a breaker to leave the neutral alone
    is that it is far less likely and in fact rather difficult for a breaker
    to be revere wired. When a breaker type GFCI operates it will nearly
    always open the ungrounded conductor. There are a lot more ways a
    receptacle type of GFCI can be supplied with the ungrounded conductor
    controlled by the grounded conductor leg of the GFCI mechanism.
     
  20. Guest

    Square D doesn't
    http://members.aol.com/gfretwell/gfci.jpg

    There is no real need for it in a breaker since you know which leg is
    hot.
     
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