Does a GFI actually trip on over current?

[eamarquardt]

Don wrote: You still have some 'misconceptions

Don Wrote: What you have on the power pole is a hot 7,200 volt wire and a grounded neutral - That's it
Gus: Not entirely true, different areas have different primary voltages. For example Ventura County has 13.8 kv and L.A. City has 4.8 kv primaries.

Don Wrote: Your house isn't directly connected to the power company at all.
Gus: You may not consider my house connected to the power company but I get a bill each month confirming the connection. In addition, I can shock myself which, for me, is convincing that a "connection" exists.

Don Wrote: The hot 7,200 volt and neutral are applied to the primary of a transformer ('pole pig') and the secondary is a centertapped 240 volt winding.
Gus: Aside from our differences on the voltages involved, we agree.

Don wrote: What runs to your home is the secondary of that transformer - 2 wire 240 volts, single phase with a centertapped 'neutral' and you get 120 volts between either of the 240 volt lines and the neutral wire.
Gus: We agree, but the 120 volt waves are 180 degrees out of phase.

Don wrote: If the 240 volt wires were out of phase with each other as you suggest, you would only have the 120 volts between one of them and the neutral . . . . across the 240 volts you would have nothing if one wire was 180 out of phase with the other wire
Gus: You have it "backawards". If the two wires are in phase, you will have no voltage difference between the two of them because they are at the same potential at the same time (in phase=the same). If the two wires are 180 degress out of phase (not the same) one will be at plus 120 while the other will be at minus 120 for a difference of 240 volts between the two (hence 240 volts). We call this single phase but it is really two phase. One phase is 120 volts to ground, the second phase is out of phase but still 120 volts to ground. Three phase is three phases that are 120 degrees out of phase from one another (unless you, like I do, generate pseudo 3 phase in your garage with an idler motor, starting caps, and running caps). This pseudo 3 phase isn't true three phase but it works well enough to run my mill and lathe. A pistol that fires each time you pull the trigger (and is not a revolver) is called an automatic pistol. A rifle behaving the same way is called semi automatic. A pistol that fires repeatedly when you pull the trigger is called a "machine pistol". A rifle that does this is called an automatic. I think that a similar confusion exists with 240 volt single phase (which really has two phases).

Don wrote: The neutral wire has nothing to do with balancing the load either - Your entire home can run off of one of the 240 wires and the neutral with nothing on the other 240 wire and it's prefectly fine.
Gus: Yer right, however, I don't know exactly why, but I've heard that it's better to have the current balanced between the 240 volt legs so there is no current flowing over the neutral. This may be more efficient in the center tapped transformer you refer to that is mounted on the power pole (if you have power poles at all). If you look at a "modern" house they are wired to attempt to balance the load.

Don wrote: Older homes were wired that way for many years until they needed 240 for something
Gus: Yer right. But we don't apparently do that anymore.

Don wrote: Proof that the 'earth' has nothing to do with it is when you plug in a 240 volt heater which runs on just those 2 hot wires . . . . no neutral or earth connection used or needed . . . . well, maybe to 'ground' the case of the heater, if it's a metal one
Gus: I agree, that I was misinformed about the earth serving as a conductor (but it can, I have been shocked several times during my time here on earth so I have empirical data that proves it so). The reason the heater runs on 240 volts is because it's hooked to two 120 volt feeds that are 180 degress out of phase. You've already stated that if you measure the two hots, you get 120 volts to neutral (ground) so they can't be 240 volts and 120 volts at the same time. They are just 240 when measured between each other.

Hope this clears things up.

Cheers,

Gus[/b]

[Alphacarina]

Gus,

You're correct . . . . to a point - The following will also clear up your conception of the 'neutral wire equalizing the current draw'

Technically, all house wiring is single phase - All we have on the power pole outside your house is single phase power . . . . at least in residential neighborhoods. We apply that single phase power to the primary of the step down transformer on the pole

On the secondary we have the stepped down household power, 240 across the two insulated wires and a neutral wire tapped off the middle which gives us 120 volts between the neutral wire and either of the hot leads

This could be all one phase (just like the primary is) and we would still have 240 volts across the secondary, but the transformer is wound so that it flips the phase on one side of the neutral wire 180 from the other side of the neutral wire

The reason this is done is simple - It cancels most of the current flow on the neutral wire and that enables us to use a smaller neutral wire than either of the hot leads . . . . saves the power company money

If we have 25 amps of 120 volt load between one of the insulated 240 volt wires and the neutral wire, then both the insulated wire and the uninsulated neutral wire have 25 amps of current flowing in them . . . . which is OK

You may have noticed that the neutral wire is smaller than either of the insulated 240 volt wires and this works because the transformer flipped the phase of the other 120 volt half 180 degrees. The net result of this is that if we have the 25 amps of 120 volt load on one side of the neutral wire and we have say 22 amps of 120 volt load on the other side, but it's 180 degrees out of phase the net result is that we have 25 amps of current flowing in one of the insulated 240 volt wires and 22 amps flowing in the other insulated 240 volt wire but we only have 3 amps flowing now in the neutral wire because 22 amps flowing 180 out from the other 25 amps in the same neutral wire cancels most of that current flow and the net result is just 3 amps of unbalanced power flowing in the smaller neutral wire

That is why one side of the 120 volt power is flipped 180 out of phase - It would still be 240 across the output of the transformer if we didn't flip it, but there would be more current flowing in the neutral wire than either of the hot wires if all of the loads were 120 volt loads

Technically though, this is all 'single phase house wiring' because that's all we started with on the pole - A single phase high voltage line

Clear as mud . . . . huh?

Don

[Larwyn]

The 240 volt single phase winding is one winding. It is center taped by the neutral, one leg is 120 volts more negative than the center tap, the other leg is 120 volts more positive than the neutral, netting a difference in potential of 240 volts. They have no choice but to be 180 degrees out of phase by virtue of the center tap. No special tricks or transformer voodoo required.

Neutral currents would only be 180 degrees out of phase if the load is pure resistive. Any capacitive or inductive load will cause a phase shift with a resulting leading or lagging power factor (imaginary power/vars).

If the voltage of the two legs of the 240 were to somehow drift from the 180 degree phase difference the voltage reading between them will decrease. If they are in phase they would read zero, same as reading hot to hot on the same buss in the breaker box. We used this fact to verify phasing on 345,000 volt transmission lines, so I am rather certain it is close to correct.........

[eamarquardt]

It's so clear that we are saying the same thing in different ways. Yer explanation of the "single phase" is correct in the way that "single phase" is "commonly" defined in the world as we know it. In "Gus's world" (as in the real world), you have two wave forms (the hot leads we agree exist) that compared to a reference potential (the neutral/ground that does not have a potential on it under ordinary circumstances) that are not the same (180 degrees out of phase) as observed on an O scope. I think they should really be defined as two phase. If you had only one hot/waveform to compare to neutral, that in my mind is properly described as "single phase". If you had two hot leads/waveforms the same voltage and in phase you could "connect" them together and you wouldn't see any change in the waveform on an O scope making them, in my eyes one single phase. 240 volt "two phase" fits, in my mind, in between 120 volt single phase and 240 volt three phase. 120 volt single phase has a "peak to peak" voltage of 240 volts , just like 240 volts single phase in the real world (called 240 volt two phase in my world) and 240 volts three phase but only reads 120 on a meter as you are reading the measurement comparing it to neutral/ground rather than from one of it's peaks to the next in the opposite direction. 240 volt single phase (in my world) would be measured at 240 volts when measured against neutral/ground and 480 volts peak to peak.

There you have it: "The world according to Gus".

I may be wrong, but my logic is irrefutable.

For clarification automatic pistol=semiautomatic rifle. Machine pistol=automatic rifle. Go figure.

Hope this clears it up.

Cheers,

Gus

[Larwyn]

Gus,

You just openend a whole new can of worms with that peak to peak statement..............

All the voltages stated are RMS Voltage. Which is .707 of peak voltage.
That 240 Volts RMS becomes close to 680 volts Peak to Peak on that there O scope.....

All this electrical stuff gives me a headache...........

[eamarquardt]

Ah, yes .707 the square root of .5 (how soon we forget). You are right that it would appear I mistated the peak to peak voltage if one was looking at the voltage on an o scope. But (although I'm making this up to defend my oversight) in my hypothetical example I was only using the o scope to observe wave forms. All of the voltage measurements were made (in my mind at least) using my Fluke 77.

Thanks for keeping me straight.

Cheers,

Gus

[Larwyn]

Yea, the Fluke 77, that is a true rms meter I believe. At least I know mine usually agrees with my Fluke 87 which I know is a true rms meter...............

[Alphacarina]

The 240 volt single phase winding is one winding. It is center taped by the neutral, one leg is 120 volts more negative than the center tap, the other leg is 120 volts more positive than the neutral, netting a difference in potential of 240 volts. They have no choice but to be 180 degrees out of phase by virtue of the center tap. No special tricks or transformer voodoo required.

Nope - Not even CLOSE!

If we were talking DC, then your 'more negative' and 'more positive' would be correct, but you can't get DC through a transformer

Alternating current is alternating current - Both sides of the centertapped neutral wire are the same so far as 'positive and negative' are concerned. The ONLY difference is that one side of the neutral is 180 degrees out of phase with the other side

A 'normal' centertapped transformer is all one phase all the way across. One side of the pole pigs secondary is wound opposite from the other, which is what creates the two sides being out of phase. Usually on schematic representations, they place a dot above or below the windings so you can keep track of the phase which lets you know that it's not a standard transformer and that it has been wound differently

Don

[eamarquardt]

If you look at an ac waveform on on o scope there are definately positive and negative parts of the wave form. If you have two sorces of potential with a common connection you can measure voltage between them because one potential can be more positive or negative than the other, thus creating a difference.

Your comment that one half of the pig pole winding is wound "backwards" from the other half makes sense. But, one could argue that since the wire or connection is continuous (but has changed direction) it is still one winding but it kinda makes sense, in a way, to call it two. In the strictest sense of the word, two independant windings would have no connection in common. I thinks that's why the term "taps" was coined.

You now seem to accept that the two drops are 180 degress out of phase.

I have never tried it, but I think you can get dc through a trasformer if you switch it on and off fast enough. If it works, it will be some form of ac on the secondary though.

I love a good tussle. I turned my issues with AT&T over to an attorney yesterday so I need a good tussle to replace my tussle with AT&T (They think I am not entitled to spend the night away from home or travel further than 60 miles from home without their permission cause I'm sick. I may be sick, but I'm not a criminal, and I'm not dead yet).

Cheers,

Gus

[Alphacarina]

You now seem to accept that the two drops are 180 degress out of phase.

Yes, you were 'technically' correct there - No doubt

I have never tried it, but I think you can get dc through a trasformer if you switch it on and off fast enough. If it works, it will be some form of ac on the secondary though.

Yes, you can alternately switch DC back and forth from positive to negative and run that square waveform through a transformer - We call those 'Inverters' which make AC from DC. The transformer cleans up the square waveform a bit and makes it look more like a sinewave, so you can run most AC powered devices with it

I can only imagine the 'tussle' you have with AT&T - Been there, done that . . . . can't imagine why anyone still has anything to do with them - Exxon either for that matter
Don

[Larwyn]

Take a look at this publication.
http://www.mhprofessional.com/downloads/products/0071467890/0071467890_ch15.pdf

I think you might be a bit amazed at just how "CLOSE" I am.

If we were talking DC we would simply magnetize the core.

The alternating current sine wave is by definition swinging positive to negative several times a second (60 in th US). At any given instant in time the two are still 180 degrees apart therefore one is always more negative or positive than the other. Otherwise there would be no difference in potential, no electromotive force, no voltage at that instant.

page 15 and 16 of the linked publication, have aplicable schmatics showing the secondary as two seperate windings as you said but jumperend mark to unmark therefore becoming one winding electrically. I fonund no mention of reversed winidings and I know in the potential transformers we used for metering and control if the windings were reversed it would be drawn as such on the schematic. I have no experience with "pole pigs" other than to ratio test and doble the them (before installation) so I will not argue the reversed winding part of this discussion.

[George Kraus]

This reminds me of the infamous "To ground or not to ground, that is the question".

George

[eamarquardt]

I don't think that you would have to reverse the polarity when switching dc on and off on the primary side of the transformer. When you turned the dc on the primary field would expand cutting the windings of the secondary driving the current one way. When you switched the dc off, the primary field would collapse cutting the secondary winding and causing the electrons to flow in the opposite direction. Thus alternating current. There are many factors, I presume, that would be involved shaping the output wave form and I can guess what they might be but couldn't predict what the output would look like under any given circumstances.

Cheers,

Gus

[Alphacarina]

The alternating current sine wave is by definition swinging positive to negative several times a second (60 in th US). At any given instant in time the two are still 180 degrees apart therefore one is always more negative or positive than the other. Otherwise there would be no difference in potential, no electromotive force, no voltage at that instant

Yes, they both swing positive and negative and by the same amount - Both sides are identical other than being 180 out of phase, so neither swings more or less positive or negative than the other

They are 'identical' 120 times per second though . . . . when both sides measure zero

ALL AC circuts have an 'instant' twice per cycle (120 time per second for us) when there is no voltage . . . . as the alternating waveform crosses through zero from positive to negative and then back again

Don

[Larwyn]

By virtue of the fact that they are 180 degreees out of phase they are swinging in oposite directions from each other. Relative to each other one peak will be at -170 volts at the same instant that the other is +170 volts. This gives you that net difference in potential of 340 volts peak, which is the 240 volts rms.

The sinewaves may be identical in apperance but they are exactly opposite in time.