GFCI operation question

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).

In alt.engineering.electrical Bud-- wrote: | 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.

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

In alt.engineering.electrical ehsjr wrote: | 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).

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

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.

Square D doesn't

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

And it saves a little money. It's looks like the GFCI/CB doesn't have the extra coil that injects the signal to detect a Neutral/Ground cross. Is that true?

EMWTK

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).

| 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.

| On Sun, 01 Oct 2006 17:14:18 GMT, "Member, Takoma Park Volunteer Fire | Department" wrote: | |>What makes you so certain that a GFCI circuit breaker does not open the |>neutral? Have you checked with several manufacturers. | | Square D doesn't |

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

MAYBE there is no real need for it. The fact that GFCI receptacles ARE opening the neutral because of the chance of miswire or usability on old wiring like K&T, we might not know if there are hazards to leaving the neutral connected. Statistics for this would also be harder to gather since if there are such hazards, they would be less often and/or less severe than with the hot left connected.

Still, I personally believe there is a small NON-ZERO hazard, generally associated with other faults or conditions. One is the possibility of higher than expected voltage on the neutral due to a loose/open neutral condition upstream. The other is that even with a normally very low neutral voltage, a solid fault from neutral to ground could still pull the 6ma that would trip the breaker. The hazard exists *IF* the breaker would continue to be activiting its mechanism to open the circuit even after it is already open, if the mechanism is not rated for continuous duty heat dissipation.

And speaking of heat, look forward, post 2008, for a lot of new home panels, the ones now FULL of AFCI breakers, to be more crowded with pig-tail wires, AND getting extra hot due to all those AFCI breakers continuously (24x356xN) using a small bit of power.

A "neutral" is not defined in the NEC, but is described in Article

310.15(B)(4) as carrying "only the unbalanced current from other conductors...".

In a 120 volt (lighting) circuit, the current is carried on both the white (or "grounded") conductor and an "ungrounded (usually black, but not necessarily) conductor. The term "neutral" refers to the neutral connection at the transformer; the center-tap. In a pure 240 volt circuit, current flows on the two phase conductors and a white (or grounded) conductor in not even needed. By introducing 120 volt circuits, the white forms one of the return legs, and carries current. (240 v between the ungrounded legs, 120 v from either leg to the neutral.)

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.

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--

| A "neutral" is not defined in the NEC, but is described in Article | 310.15(B)(4) as carrying "only the unbalanced current from other | conductors...".

"Neutral conductor" is defined in the NEC. The term is used in many places. I fully understand what a neutral is. Are you raising an issue about its common or formal usage?

| In a 120 volt (lighting) circuit, the current is carried on both the white | (or "grounded") conductor and an "ungrounded (usually black, but not | necessarily) conductor.

If you are wanting to get very specific, it's the insulators that have the color. The current is carried on the (usually) copper metal (with a magnetic field, of course).

The code requires the grounded conductor be identified well (e.g. continuous color, not just marked at each end). Others have more leeway.

| The term "neutral" refers to the neutral connection at the transformer; the | center-tap. In a pure 240 volt circuit, current flows on the two phase | conductors and a white (or grounded) conductor in not even needed. By | introducing 120 volt circuits, the white forms one of the return legs, and | carries current. (240 v between the ungrounded legs, 120 v from either leg | to the neutral.)

You could tap the transformer off-center a bit if you wanted to and have

115 volts on one side and 125 volts on the other side. Would you call that a "neutral"?

So tell me ... what happens if you have a couple of very low power factor loads, one on each 120 volt side, where one is very inductive and the other is very capacitive? Now how much current flows on the "neutral"?

| 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.

I see very little use in error in the US. Neutral does not mean grounded, but it generally implies that because that is the required way to wire it up. See NEC 250.26(2). The two terms "neutral conductor" and "grounded conductor" do have different meanings, but are associated with the same wire because that is the required way.

Single phase in Europe is generally 2-wire service. You can still call one wire neutral because it may well be the wire connected to the real neutral point in either a single phase transformer (center tapped 230/460) or a three phase transformer (connected to the star common). But it is grounded and thus (also) correct to call it a grounded conductor. If the service is coming from a 2-wire transformer all by itself, then it's not really neutral; it's just grounded.

On Tue, 03 Oct 2006 02:55:28 -0500 Bud-- wrote: | snipped-for-privacy@ipal.net wrote: |> 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 |> | | 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.

Phil, give me an example of a neutral that is not grounded in an NEC compliant circuit. I do understand in a corner grounded delta the grounded conductor does not carry the imbalanced current but that is the only example I can think of when a grounded circuit conductor is not a neutral. It is still identified white or grey.

Uh, I thought the 'current injection' was on the groundED conductor. No need to inject a signal in the ungrounded conductor ('hot') as a fault there will be sensed immediately.

A 'current' signal is injected on the groundED conductor (neutral) so if it is connected to the groundING conductor downstream, the GFCI will trip

*immediately*, not just when a load is connected (been there, done that :-(

daestrom

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.

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.

On Wed, 04 Oct 2006 13:03:51 -0400 snipped-for-privacy@aol.com wrote: | On 4 Oct 2006 13:09:46 GMT, snipped-for-privacy@ipal.net wrote: | |>I see very little use in error in the US. Neutral does not mean grounded, |>but it generally implies that because that is the required way to wire it |>up. See NEC 250.26(2). | | | Phil, give me an example of a neutral that is not grounded in an NEC | compliant circuit.

I know this isn't exactly what you might be thinking of, but since this is more about term definitions than about practical wiring, let me point to 411.5(A):

Grounding. Secondary circuits shall not be grounded.

Of course that's part of article 411 covering lighting systems operating at 30 volts or less. Typical systems operate at 12 volts. It could be quite practical to construct such a system using a transformer with a secondary supplying 24 volts which is center tapped, giving 12 volts in two separate poles, e.g. a 12/24 volt system, very much like the common North American single phase 120/240 volt system, except that the neutral is not grounded per 411.5(A).

OK, so there, I met the letter of your request.

And we might also consider 250.21 and 250.22, although I don't know that I would want anything more than a 2-wire system for any of those.

What is not clear to me, yet, is whether white or gray is a valid color for the insulation of that UNgrounded neutral wire on the 12/24 volt ungrounded lightning system described above. 200.7(B) and 250.20(A) don't make this obvious for an article 411 system.

| I do understand in a corner grounded delta the grounded conductor does | not carry the imbalanced current but that is the only example I can | think of when a grounded circuit conductor is not a neutral. It is | still identified white or grey.

Just because the voltage and current phases are systematically not at a nice 180 degrees apart, is not a cause for me to not refer to it as a neutral. Consider the rather common case in many locations where single phase service is provided by supplying 2 phases of a 3 phase system at

120/208 volts. NEC 250.26(5) refers to this as a neutral conductor. Why would two phases at 120 degrees consider it as a neutral and two phases at 60 degrees not? Of course there is an imbalance present as 310.15(B)(4)(b) addresses by requiring it to be counted as a current carrying conductor for derating purposes, where at 180 degrees is would not need to be counted.