GFCI operation question

|> In Europe, the term "neutral" does include a grounded conductor in a 120 v |> circuit. In the states the term is used interchangeably but in error.
| | In Europe, there are no 120V circuits, and "neutral" is a supply | current carrying conductor which is at or near ground potential.
But that doesn't really change the meaning's origin. The first power systems were three phase to drive motors. I don't know if delta was used much way back when, but with star/wye configurations, you do have a genuine neutral. When single phase at 240v is taken from that, the neutral is still there. It just doesn't have enough phases brought in to take the neutralizing role there.
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     snipped-for-privacy@ipal.net writes:

The neutral role is still there, i.e. it's still at or near ground potential.
Now there are some single phase supplies in europe which don't have a neutral, but they are much less common and only in a few countries (not UK). An example is a single phase supply from a corner grounded delta, where both of the lines are taken from a non-grounded corner.
There are also IT supplies which are isolated with just a resistance to ground to prevent the secondary capacitively floating up to the much higer primary voltage. Strictly the side with the resistor to ground is still called a neutral, although it might be some way from ground potential. Again, I believe some parts of Europe use this, but it only occurs in the UK on standalone generators, not from the public supply.
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| snipped-for-privacy@ipal.net writes:
wrote:
|>|> In Europe, the term "neutral" does include a grounded conductor in a 120 v |>|> circuit. In the states the term is used interchangeably but in error. |>| |>| In Europe, there are no 120V circuits, and "neutral" is a supply |>| current carrying conductor which is at or near ground potential. |> |> But that doesn't really change the meaning's origin. The first power |> systems were three phase to drive motors. I don't know if delta was |> used much way back when, but with star/wye configurations, you do have |> a genuine neutral. When single phase at 240v is taken from that, the |> neutral is still there. It just doesn't have enough phases brought |> in to take the neutralizing role there. | | The neutral role is still there, i.e. it's still at or near ground | potential.
But that's not what the meaning of neutral is. It's neutral whether it is grounded or not. In cases where there are 2 or mroe phases, the idea is that when things are in balance, there is no current on the neutral. It was neutralized by the balance. But I think the meaning really comes from the neutral point in the transformer winding of the secondary.
| Now there are some single phase supplies in europe which don't have | a neutral, but they are much less common and only in a few countries | (not UK). An example is a single phase supply from a corner grounded | delta, where both of the lines are taken from a non-grounded corner.
Apparently these are older connections. From what I gather, the first power in much of Europe in the late 1800's was 220/127 three phase. It appears that predated Edison supplying light to New York, so it seems he took the 220 voltage and split it for DC. He likely also realized, in all his light bulb work, that a lower voltage worked better on the filament. I've heard that the 220/127 can still be found in some remote locations like way north Norway and rural parts of Spain. A friend has reported seeing the remnants of 220/127 wiring in buildings in Germany predating WW1.
| There are also IT supplies which are isolated with just a resistance | to ground to prevent the secondary capacitively floating up to the | much higer primary voltage. Strictly the side with the resistor to | ground is still called a neutral, although it might be some way from | ground potential. Again, I believe some parts of Europe use this, | but it only occurs in the UK on standalone generators, not from the | public supply.
The reason they use that resistance instead of a solid ground is to avoid single fault failures. But during that time, one hot line is now grounded.
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wrote:
[snip]

Even when that's exactly what you want.

[snip]
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Mark Lloyd
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Mark Lloyd wrote:

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.
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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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| 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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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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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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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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On 1 Oct 2006 10:18:38 GMT, snipped-for-privacy@ipal.net wrote:

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
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On Sun, 01 Oct 2006 13:07:48 -0400 snipped-for-privacy@aol.com wrote: | On 1 Oct 2006 10:18:38 GMT, snipped-for-privacy@ipal.net wrote: | |>So why is the neutral opened? | | 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
So basically they will work miswired (at least without a ground attached, if there is a way for them to detect the miswire with a ground reference).
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snipped-for-privacy@ipal.net wrote:

Easy to find the hot with a neon test light by touching one lead and probing with the other.
Opening both wires also protects from miswiring by people who don't know what they are doing. GFCIs are now fairly idiot proof.

They don't need and don't use the ground wire, except to pass it through to the receptacle, so they work with line H-N reversed. One would presume the detection of a downsteam N-G connection at no load would not work as the current injection is in the hot wire, but downstream N-G connection would cause a trip when there is a load.
bud--
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| snipped-for-privacy@ipal.net wrote:
|> | |> |>So why is the neutral opened? |> | |> | 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 |> | | Easy to find the hot with a neon test light by touching one lead and | probing with the other. | | Opening both wires also protects from miswiring by people who don't know | what they are doing. GFCIs are now fairly idiot proof. | | |> So basically they will work miswired (at least without a ground attached, |> if there is a way for them to detect the miswire with a ground reference). |> | | They don't need and don't use the ground wire, except to pass it through | to the receptacle, so they work with line H-N reversed. One would | presume the detection of a downsteam N-G connection at no load would not | work as the current injection is in the hot wire, but downstream N-G | connection would cause a trip when there is a load.
If there is a voltage imbalance in the system, there could be enough to have at least 6 milliamps flowing down the N of a circuit and back up the G of that circuit. Remember, electricity does NOT take the best path to return ... it takes ALL the paths. So you really could see a wiswired GFCI just up and trip with no load downstream of it.
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wrote:
| Don't see what your thinking there. If the groundED conductor has no load | on it, then it's at the same potential at the GFCI as it is in the service | panel. Ditto for the groundING conductor, so there is no current flow | through a groundED - groundING conductor fault downstream of the GFCI.
If the groundED conductor splits off somewhere between the point it is bonded to ground, and where the GFCI is, then a load on another circuit at that point can create the voltage drop on the feeder to that point, and give you the voltage. Think of a subpanel.
My home design plan currently involves keeping subpanels as close to the main panel as possible, and oversizing the feeder to the subs. A more extreme solution would be to have separately derived systems for subs.
| Except... GFCI's deliberately inject a small signal into the 'hot' and | 'neutral' that is the same in both. Doesn't affect the load normally | (common mode signal), but it *will* generate enough current through a | 'neutral-ground' fault downstream to trip the GFCI with no load attached. | So a groundED - groundING fault downstream is detected and trips the unit, | regardless of load.
I wonder if this is the cause of being able to dangerously trip GFCI receptacles with a radio transmitter.
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wrote:

That will raise the groundED conductor potential, yes. But that alone won't trip the GFCI, would also need a groundED-groundING fault downstream of the GFCI. And *that* sort of fault will trip it right away, regardless of a sub-panel issue or not (because of the 'signal' injected into the groundED conductor by the GFCI itself).

May be. Old GFCI's didn't have the extra circuit to inject this signal, but newer ones do (think it was a code change that added it).
daestrom
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wrote: |
| wrote: |> |> | Don't see what your thinking there. If the groundED conductor has no |> load |> | on it, then it's at the same potential at the GFCI as it is in the |> service |> | panel. Ditto for the groundING conductor, so there is no current flow |> | through a groundED - groundING conductor fault downstream of the GFCI. |> |> If the groundED conductor splits off somewhere between the point it is |> bonded to ground, and where the GFCI is, then a load on another circuit |> at that point can create the voltage drop on the feeder to that point, |> and give you the voltage. Think of a subpanel. |> | | That will raise the groundED conductor potential, yes. But that alone won't | trip the GFCI, would also need a groundED-groundING fault downstream of the | GFCI. And *that* sort of fault will trip it right away, regardless of a | sub-panel issue or not (because of the 'signal' injected into the groundED | conductor by the GFCI itself).
But what if the fault downstream is not a solid fault, but a person contacting the neutral wire.
What it comes down to, is I want GFCI protection that always opens both wires. And I want it to work even if AFCI in installed. My easier posting (maybe not in this thread) described how GFCI could fail with combination AFCI installed, leaving this vulnerability.
1.
The combination AFCI+GFCI might trip on the fault first, leaving the downstream GFCI unpowered to do its thing, leaving the neutral in a connected state, with a reduced but non-zero hazard being present.
2.
The fault on the neutral might cause GFCI tripping to operate in a continuous manner, potentially burning out the GFCI solenoid. That process could get worse.
I'm not yet convinced that combining GFCI protection in AFCI is such a good thing. There is the neutral issue, as well as the residual charging current issue (for long branch circuits). If the load is far from the service entrance, you either run a long branch and have the excess charging current diminish the GFCI range and increase the nuisance trips, or you use a subpanel and raise the neutral voltage above the bonding point, or you have the expensive of "one circuit" subpanels for each place that has special risk for GFCI (wet places), or use a transformer with a newly derived neutral bonded to the feeder grounding wire.
If you think a neutral wire is safe, then I'll let you be the one to try it. Stand barefoot on a wet concrete floor at ground level, and lick a bare neutral wire with your tongue :-) I certainly would not ever do that.
|> I wonder if this is the cause of being able to dangerously trip GFCI |> receptacles with a radio transmitter. |> | | May be. Old GFCI's didn't have the extra circuit to inject this signal, but | newer ones do (think it was a code change that added it).
So maybe it is the newer GFCIs that are vulnerable to the radio because of their circuit that checks this injected signal?
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