GFCI operation question

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wrote:

Which is what I wanted. This GFCI is installed inside (where no GFCI protection is needed) and it controls an outside light. The GFCI acts as a light switch (at least it used to, before I had to replace it with one of those "improved" ones).

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86 days until the winter solstice celebration

Mark Lloyd
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| Mark Lloyd wrote:
|> 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.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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It is more likely that the rf is getting into the GFCI electronics directly, rather than through the toroid. I suspect the input to the chip is fairly high impedance, and there may even be some non-linearity that acts as a detector.
I know you have mentioned this before, and although I have never experienced it, I can easily believe that it can happen. I might try some experiments to replicate it. Do you have any idea of how strong and at what frequency the rf was?
Ben Miller
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Benjamin D. Miller, PE
B. MILLER ENGINEERING
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When my house was built I had four post lights along my driveway. Two of them had outlets so a GFCI breaker was installed in the circuit box. The bathroom lights were on the same circuit. Every time we had a thunder storm, the GFCI would trip. I had to install a standard breaker. I almost never use the outlets and if I do, I wear rubber gloves.
---MIKE---

>> (44° 15' N - Elevation 1580')
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If the 4 posts are daisy chained, install a GFI outlet on the first one and feed the rest from the output terminals of the GFI.
You may wear rubber gloves. Will your workmen, kids or others?
--
Rich Greenberg N Ft Myers, FL, USA richgr atsign panix.com + 1 239 543 1353
Eastern time. N6LRT I speak for myself & my dogs only. VM\'er since CP-67
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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.)
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| |> 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.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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sorry I digress, but why is it wrong to call the white wire a neutral? if the white wire is not the neutral, then which is the correct neutral wire?
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peter wrote:

I agree that technically a neutral only carries the unbalanced current in a multiwire set (a white wire in a particular application). However neutral is very commonly used (at least in the US, except by the NEC) to describe the groundED conductor in general. Using the terms groundED (white wire) and groundING (green wire) leads to confusion, as demonstrated by Ed. It took me a while to be able to read groundED and groundING without having to think which was which. IMHO it is entirely reasonable to use "neutral" for the white wire.
bud--
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PPS wrote:

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
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| 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).
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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snipped-for-privacy@ipal.net wrote:

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.
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous
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In alt.engineering.electrical Member, Takoma Park Volunteer Fire Department
| What makes you so certain that a GFCI circuit breaker does not open the | neutral? Have you checked with several manufacturers.
I've looked at the engineering diagrams, cut-aways, and schematics. There are no contacts for interrupting the neutral wire.
| 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.
So basically, there is no goal or interest in specifically opening the neutral. It's just a case of opening both in situations where either might be the neutral.
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|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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wrote:

Let me say what I said another way. GFCI outlets and circuit breakers measure if there is a difference between the amount of current going throught the hot wire and though the neutral wire. If they are the same, the gfci sees no problem. Having a loose connection does not mean that will happen. Using an appliance that shorts to your body and from there to some other path than the neutral wire *would* cause it to trip.
OTOH, if you took two all-metal screwdrivers, one in each hand, and stuck one into each of the slots in an outlett, even a GFCI outlet, you could burn your heart to a fine grey ash, and the breaker would not trip. Because the same amount of current was going through the two conductors.

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Methos wrote:

There's all kinds of "bad connections". If the bad connection resulted in a difference of 5 mA or more between the current in the neutral versus the current in the hot wire, the GFCI would trip. The example you gave would not cause the GFCI to trip.
Ed
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As others have mentioned, a GFCI would probably not trip. They sense current differences, and usually have current overload sensing in them also. But a bad connection causing the terminal to warm up would not trip it unless it got very hot, and even then the results are indeterminate.

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So far there has been a lot of misinformation in replies to this thread.
Only the smoke will indicate a simple HOT connection. If there is any arcing a AFCI should detect the fault and disconnect.
Quote
"The “AFCI” is an arc fault circuit interrupter. AFCIs are newly-developed electrical devices designed to protect against fires caused by arcing faults in the home electrical wiring."
****
A GFCI will only protect from differences in the current flowing in the two conductors beyond the GFCI. It will cutoff the current when a very small current difference, 5 or 30 ma., is detected and should do it quick enough to save a person from electrocution.
Neither device is intended to protect from voltage spikes and neither device can detect a simple hot connection.
A hot connection alone will not csause a difference in current between the 2 legs of the circuit, only a ground fault can cause that and a GFCI should detect that.
--
John G

Wot\'s Your Real Problem?
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