GFCI operation question

Careful now, all that twisting around and you might hurt yourself.

;-)

Reply to
gfretwell
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In a corner ground there is 240v between all current carrying conductors and there is no unbalanced current in the center tapped sense of the word. This will actually look a lot like single phase until you check the voltages . (2 blacks and a white with a 2 pole breaker.) It is used when it is all balanced 3 phase loads, typically a motor.

Reply to
gfretwell

| 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.

Reply to
phil-news-nospam

In Europe, there are no 120V circuits, and "neutral" is a supply current carrying conductor which is at or near ground potential.

Reply to
Andrew Gabriel

It is on both hot and neutral, common mode. For N-G detection it is only required on the N as you say, but unless it is also applied to the hot in common mode form, it would also appear across all loads downstream, which would require a much more powerful current source in the first place.

Reply to
Andrew Gabriel

And just to correct myself, it's a voltage source, not a current source. Current only flows when there's a N-G fault.

Reply to
Andrew Gabriel

In alt.engineering.electrical Andrew Gabriel wrote: | In article , | "PPS" writes: |> 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.

Reply to
phil-news-nospam

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.

Reply to
Andrew Gabriel

In alt.engineering.electrical Andrew Gabriel wrote: | In article , | snipped-for-privacy@ipal.net writes: |> In alt.engineering.electrical Andrew Gabriel wrote: |>| In article , |>| "PPS" writes: |>|> 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.

Reply to
phil-news-nospam

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

Reply to
daestrom

Yes, the ones I have seen it's nothing more than a toroid core that the 'hot' and 'neutral' pass through, with a few turns of a second 'winding' that is fed from hot and neutral 'upstream' of both this toroid and the sensor one. Perhaps a resistor in series with this 'primary winding', can't remember now. The winding is fed from 'across the line', and the 'output' is a common-mode signal on groundED and ungrounded current carrying conductors.

daestrom

Reply to
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. |>

|> 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?

Reply to
phil-news-nospam

On top of that, consider open neutral events. How many electricians have been injured or died from miswired milti-wire branch circuits? How many homes have had devices wiped out from open neutral between the transformer and main panel?

Reply to
Matthew Beasley

| | On top of that, consider open neutral events. | How many electricians have been injured or died from miswired milti-wire | branch circuits? | How many homes have had devices wiped out from open neutral between the | transformer and main panel?

I've seen 2 open neutral events in homes. I lived in one, and we were lucky enough to not lose anything except the evening dinner. My mother thought it was funny that the light over the bar opening would go up and down in brightness as she turned burners on the stove on and changed their setting. I was 14 at the time, but I knew what an open neutral could do and immediately recognized it. Turns out that light had been tapped from the stove circuit, and was the only thing like that. But it got some other wiring issues in the house fixed up in a hurry, like the open split bolt splice hanging on nails on a wooden board that fed the stove. At first I thought that was where the neutral was open. But as it turns out, it was open in the fuse box. But the electrician got it all cleaned up that day, finally. The other even I saw was in a neighbor's house. I never found out where it was caused from, but she did complain to my dad that the clock built in to her stove had quit working and was smoking. We got her disconnected, but she did have to get a new stove as a result.

Reply to
phil-news-nospam

ASSuming they are qualified and have a little experience, I would think the answer would be damn few.

Likely, quite a few. It's happen to me. But as far as I could determine I didn't lose anything important. Some of the expensive stuff seems to be pretty resistant to over voltage damage (computer power supplies and electronics) or has thermally protected motors or whatever. Most of the interior lamps are CFs but in any case I didn't find a large numbr of burned out lamps of any type.

Reply to
John Gilmer

Even among the experienced, there is still the risk of miswired circuits. Even measuring the current before opening the neutral can fail if the load is intermittent, like a water cooler or other thermostatic controlled device.

If it gets anywhere near the full 240V possible, not many consumer electronic devices can take that.

Reply to
Matthew Beasley

| If it gets anywhere near the full 240V possible, not many consumer | electronic devices can take that.

OTOH, autoranging switch mode power supplies seem to have no trouble. the just have short switch-on times for the higher voltage, up to the voltage they are rated for breakdown, which for international units is going to be at least 250 volts as found in China. There may even be a chance they can work on 277 volts in the USA (though not officially rated at such because who would ever need to do that).

I have heard that some of the switch mode supplies that have the switch to change between voltages (usually marked as 110/220 or 115/230) are not really change a transformer between series and parallel, but rather are just changing some component values in the circuitry to operate better at the selected voltage (maybe to reduce harmonics or improve the power factor at that voltage).

The more such power supplies we can encourage electronics and appliance manufacturers to use, provided the harmonics and power factor issues are not a problem, the better off we are.

Reply to
phil-news-nospam

More than one IT equipment manufacterer has started to produce special supplies for China / India. Those supplies will work on US 277 V. Off label, but within specs for most of them. I don't think any of the "special" ratings are published.

Yep, autorangers have no problem. I have used them on 240V or 480V with a control power stepdown to 120V because it gives such a good margin for overvotlage - double input is OK

Autorangers are common on laptops, cell phone chargers, battery chargers, or other devices that may be used internationally. They tend to be in the lower power rated supplies.

120/240 supplies switch the rectifier type depending on input voltge. In the 240V position, they are a full wave rectifier. In the 120V position they are configured as voltage doublers. Either way, the bus voltage is supposed to be around 280V to 350V. In the 120V position, 240V will take them out. Most PC supplies are this type. Some are autoswitching, but a sudden increase from 120V while operating can take them out.

Consumer electronics are often 120V only. This is because their high volume and NA unique requirements (NTSC, ATSC, frequency alocation) make it cost effective to use 120V only supplies. With these also, 240V will wipe them out.

Reply to
Matthew Beasley

Quite possible. But if you are just living "normally" when the neutral goes out you end up with some light VERY bright and some very dim.

And, from my experience, the dropped neutral (from the service drop) doesn't take out much (if anything).

Of course, when the service drop neutral goes there is still the earth path between the power company ground (which "around here" is said to be 'zero ohms') and whatever ground that is bonded to neutral in the panel and meter base.

Another thing I had going for me is that I have a metalic connection from my deep well right up through my water tank to the household grounding wires. If you included the water heater ground there is the equivalent of a #10 wire between the well metalics and the panel ground. The negative is that the power company ground is 400' away from my meter box.

More urban folks may not have such a good house ground and urban low voltage distribution may not ground as effective as the rural providers do.

When in comes to a three wire 240/120 load circuit, of course, a lifted neutral might, for example, power a TV set and a toaster. When the neutral goes the TV would likely see no voltage. When someone decides to use the toaster the TV may become toast!

Reply to
John Gilmer

| 120/240 supplies switch the rectifier type depending on input voltge. In | the 240V position, they are a full wave rectifier. In the 120V position | they are configured as voltage doublers. Either way, the bus voltage is | supposed to be around 280V to 350V. In the 120V position, 240V will take | them out. Most PC supplies are this type. Some are autoswitching, but a | sudden increase from 120V while operating can take them out.

But autoswitching is NOT the same as autoranging, correct?

So the autoswitchers are best switched only from a power coming on state?

Can the autorangers function for any voltage in between 120 and 240?

The impression I got from the designs I saw for a switch mode power supply, which was not really complete info, is that on a higher voltage the time the current flowed was shorter, and for a lower voltage it was longer. But maybe that was just for some brownout handling. I have seem power go completely out for an instant, long enough for the lights to go all the way out and even for clocks to lose time, and yet, my computers stayed up. I guess the capacitors have enough reserve and I'm not loading them up on the DC side too much.

| Consumer electronics are often 120V only. This is because their high volume | and NA unique requirements (NTSC, ATSC, frequency alocation) make it cost | effective to use 120V only supplies. With these also, 240V will wipe them | out.

As long as a single voltage supply has a cost lower than a dual voltage by an amount greater than the savings of having only one type of supply being manufactured and in inventory, then I guess we wil continue to see them, and have damages.

So why are PC supplies pretty much all dual voltage or autoranging? I can see that for laptop external power converters, as they may be used in some other country. But for towers that don't move around much?

Reply to
phil-news-nospam

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