240v debate....

[david luchini]

So, the relationship of the measurements is critical when describing the system.

So saying, two waveforms in phase V1n and Vn2 which add together to V12, is a perfectly valid statement.

Yes, that is correct, V1n + Vn2 = V12. It is also correct that V1n-V2n = V12.

I think it would be most common to describe the two 120V legs of a 120/240 single phase system as "A-to-neutral" and "B-to-neutral" rather than "A-to-neutral" and "Neutral-to-B." So V1n-V2n = V12 would be my preference.

 

[jim dungar]

I wouldn't call it critical, it is merely a reference point, other reference points will produce different results. The relationship between two waveforms depends on which on is taken as the refrence point. It is sort of subject/object relationship.

So while choosing the reference point is subjective, the system description is dependent on which point is chosen.

 

[jim dungar]

Yes, that is correct, V1n + Vn2 = V12. It is also correct that V1n-V2n = V12.

I think it would be most common to describe the two 120V legs of a 120/240 single phase system as "A-to-neutral" and "B-to-neutral" rather than "A-to-neutral" and "Neutral-to-B." So V1n-V2n = V12 would be my preference.

There are transformers with both 24V and 120V output connections, would you describe these two waveforms as being 180? out of phase?

My preference is to mention the neutral as my reference point when I have used it as such, after all there are many times a neutral is not used.

 

[charlie b]

What debate? . . . The higher the voltage the more severe the effect of the electrocution on the body will be. . . . Neither is debateable.....

I will debate that claim, by simply stating that dead is dead, and "electrocution" means dead. And if you meant that higher voltage gives a more severe shock, then I will restate that 120V and 240V will make you equally dead, and no less dead than 60V would have made you. Neither 120V nor 240V is "safer" than the other. That is the essence of the original question.

 

[mivey]

So while choosing the reference point is subjective, the system description is dependent on which point is chosen.

What do you mean by "system descriptions"? If you mean the relationship between the voltages, the reference point absolutely is critical because ANY voltage must have a reference point or it is meaningless.

There are transformers with both 24V and 120V output connections, would you describe these two waveforms as being 180? out of phase?

Not enough information. What waveform are you talking about? Without a reference frame, "24V" and "120V" have no discernable relationship other than they have different magnitudes.

My preference is to mention the neutral as my reference point when I have used it as such, after all there are many times a neutral is not used.

If you want to have any useful information, ANY voltage must be associated with some reference point and it should be clear what you have used as a reference, even if that reference is not the neutral.

 

[Besoeker]

So, the reference point is absolutely critical when describing the relationship between the two waveforms.

We are looking at a 120V-0-120V transformer.
There are thus three connections. The two ends of the winding and the centre tap or mid point of the winding. If you chose one end as the reference point and look with the scope simultaneously* at the mid point and the other end, then, of course you will get two waveforms that are in phase with each other - but of different magnitudes.
i.e 120V and 240V.
If you want to compare the two 120V sections of the transformer with respect to each other to determine their phase relationship you have to use the centre tap as the reference point.

*If you don't do so simultaneously, you can't determine the phase relationship.

 

[Besoeker]

That is the whole point. To say they are out phase without including the reference point is technically mis-leading.

I did include a reference point.
This from my post #49:
It's what you would see and do see on an oscilloscope using the the neutral as the common point.
How else can you determine their phase relationship?

 

[Besoeker]

A 180? phase difference is an 8ms time delay at 60Hz (or 10ms @50 Hz). If this assertion that a 180? phase shift truly existed, then it would mandate that if a waveform artifact (like a spike) were to occur in the primary winding at T_o then the transformed spike would allegedly occur in the secondary A-phase at T_o, but in the B-phase at T_o + 8ms.

It isn't a time delay. With respect to the neutral, both waveforms cross zero at the same time - they just then go in different directions. See my earlier point about where they are at after quarter of a cycle. At the same instant in time.

Besoeker and many others have chosen to invert one of the signals as a convenience for visualizing the system, and that is perfectly fine. The error comes about when you define the system as though it has this inversion and time-shift. The inversion and time-shift are not real, but are only mathematical tools used to make their analysis fit their needs.

I have inverted nothing.

Besoeker, my apologies for assuming that this was something patently obvious to anyone with an engineering degree. However, if you spend a little time giving this some critical thought, I am sure that you will see the distinction between how a system is perceived versus how it is defined, and it cannot be defined with this artificial time delay.

There is no time delay. See above. Phase difference does not equal time delay. Anyone with an engineering degree ought to be able to understand that.

 

[mivey]

...The error comes about when you define the system as though it has this inversion and time-shift. The inversion and time-shift are not real, but are only mathematical tools used to make their analysis fit their needs.

...The whole point of the discussion is education. People have become so accustomed to looking at it as a phase shift, that they have lost sight that this is only a tool for viewing it. They have taken this to mean that it is phase shifted, not simply being viewed as phase shifted.

What makes you think the phase difference in the waveforms is not real? Of course it is real because the math is just modeling the real world. If the phase difference were not real, we could not really make use of the phase difference in the physical world. Here is a real world example where we make use of the physical reality of the difference in phase:

Open Wye to 4-wire Wye secondary (0? displacement):
.
A----------------)H2..X4(---------------------a..v@0?
.................)......(
.................)......(./\.v@0?
.................)......(
.................)....X3(------------o
........V@0?./\..)...................|
.................)....X2(------------o
.................)......(............|
.................)......(.\/.v@180?..|
.................)......(............|
....o------------)H1..X1(------------|---o
....|................................|...|
....|................................|...|
....|................................|...|
B---|------------)H2..X4(------------|---|----b..v@240?
....|............)......(............|...|
....|............)......(./\.v@240?..|...|
....|............)......(............|...|
....|............)....X3(------------o---|----n..0@0?
....|.V@240?./\..)...................|...|
....|............)....X2(------------|---o
....|............)......(............|
....|............)......(.\/.v@60?...|
....|............)......(............|
N---o------------)H1..X1(------------|--------c..v@120?
....|................................|
...Gnd..............................Gnd

You should be able to plainly see that if the X43 voltage was not really different in phase from the X12 voltage then this would not work in the real world. In fact, it does work and is a common transformer configuration and does not require "magic" transformers.

 

[iwire]

So here I am wondering ........... has any of this helped the OP in the least?

I wanted to run a pump at 240v vs 120v, for obvious reasons, voltage drop, wire size, etc. But... I get this a lot from people, 240v is more dangerous. So I'm looking for a better way to explain to people that its just as safe as a 120v circuit but with better benefits.

 

[kwired]

Of course 120V is a little safer than 240V. But with that same logic, these are even safer:

Safer when talking risk of electrocution. I have heard many windmill accident stories. Some ranchers with remote pastures still use them for pumping water for cattle. I know a well man that fell off one, was in hospital for long time but did recover.

So here I am wondering ........... has any of this helped the OP in the least?

I don't know, seems to me you could have a DC source with a center tap and phase angles won't mean anything there - and there is still similar voltage relationship between the taps.

 

[mivey]

So here I am wondering ........... has any of this helped the OP in the least?

Only if the OP understands and/or agrees with what I have posted.

In reality, I think while we are off topic slightly it is not as far off as we could get. I think you and I generally agree that as voltage goes up, in some respects so does the danger (sorry Charlie). I think this was mentioned but I don't feel like looking back: the conductor-to-conductor contact "danger" has increased but the relative conductor-to-ground exposure is the same for 120 or 240 volts and I think it is safe to assume that line-to-ground contact is a large part of the accident pool.

I think it is a fair question to ask: "if the line-to-ground voltage is essentially 120 volts for both 120 and 240 volt systems {at least for the ones we normally see}, how do we still get 240 volts?". One must understand the relationship between voltages that have a grounded neutral reference (X2 & X3 grounded neutral). In this line of questioning, an X1 or X4 reference would not be as clear.

Another thing that shifts the "safety factor" is that the OP should also understand that a neutral, even though it is grounded at the panel, can have a voltage and most definitely is a current carrying conductor. No telling how many have been shocked by thinking the neutral was safe to open because they are thinking of it as earth instead of a conductor. This, to me, makes 120 volts "more dangerous" in other respects.

 

[mivey]

Another thing that shifts the "safety factor" is that the OP should also understand that a neutral...

I should have said reader. I know Stickboy knows all that.

 

[Rick Christopherson]

What makes you think the phase difference in the waveforms is not real? Of course it is real because the math is just modeling the real world. If the phase difference were not real, we could not really make use of the phase difference in the physical world.

No, the phase difference is not real. When you move your reference point, you are changing the polarity (i.e. a minus sign), but instead of just using a minus sign, you have instead inserted a 180? time shift in the phase to achieve the "effect" of a minus sign.

It is not real-world correct nor mathematically correct, but it does work out as a tool, simply because the input signal is assumed a perfect sine wave with its expected symmetry about pi. If you doubt this, then simply hook up a non-symmetrical wave input to your transformer and look at the resulting wave forms on your scope. You will see that they are not time-shifted on your scope, but instead are simply inverted in magnitude.

No, I didn't overlook your previous "signals and systems" comment. It was wrong in this application and was ignored for being inapplicable and off-topic. As it applies to this discussion, a phase shift is a time shift. If this isn't clear to you, then redo the mathematics with a non-symmetrical waveform just like the above example.

A simple example of this is to put a diode (half-wave rectifier) on your primary side. This will remove the symmetry about pi of the source waveform. If you truly had a 180? phase shifted output, then you would see the two phases no longer being mirrored, but instead shifted. You would have half-wave rectification from Neutral-to-A, half-wave from Neutral-to-B, but A-to-B would still remain full-wave, un-rectified. If you can design a transformer that duplicates the above scenario, then I will personally pay for your patent application and submit your design for the Nobel Prize.

 

[Rick Christopherson]

A simple example of this is to put a diode (half-wave rectifier) on your primary side. This will remove the symmetry about pi of the source waveform.

By the way, here is the follow-up mathematics for the above for you to consider. (I can't think of the mathematical operation representing a half-wave rectification, but you should be able to understand the concept.)

sin(ωt + 0?) = -sin(ωt + 180?)
abs[sin(ωt + 0?)] = abs[sin(ωt + 180?)].... (positive magnitude, full-wave rectification)
rectified[sin(ωt + 0?)] ≠ rectified[sin(ωt + 180?)]......(positive clipped magnitude, half-wave rectification)

 

[Besoeker]

No, the phase difference is not real. .

Not real?

OK. I'll refer you back to a point I made earlier.
A 120V-0-120V centre tapped transformer. Two live wires. One neutral. Each side feeds a 12 ohm resistive load. Each resistor thus takes 10A.
What is the current in the neutral and why? Ponder that.

Disconnect one of the loads.
What is then the current in the neutral. And why?

Think about it.

 

[Rick Christopherson]

Not real?

OK. I'll refer you back to a point I made earlier.

And I refer you to the posting directly above the one you just made. If your phase shift was real, then putting a diode on the primary will result in the shift I described. If you can't replicate it with your scope, then you don't have a phase shift--you have a polarity reversal. They are not the same.

The situation you described is nothing more than a canceling of magnitudes. It does not prove your point, and that is why I did not comment on it when you made it. If you want me to comment on these things, then you need to put some more thought into them before making them. It was not well thought out and I do not have the patience for that, as you may have noticed.

 

[Rick Christopherson]

A 120V-0-120V centre tapped transformer. Two live wires. One neutral. Each side feeds a 12 ohm resistive load. Each resistor thus takes 10A.
What is the current in the neutral and why? Ponder that.

Disconnect one of the loads.
What is then the current in the neutral. And why?

Think about it.

By the way, instead of just blowing you off without explanation for a poorly thought out argument, I will take the time to explain to you why this was so poorly thought out, and doesn't prove your "phase shift" conclusion.

Do the same thing with 2 batteries and you get the same answer. That is why it wasn't worth addressing when you brought it up several postings ago. I am sorry, but that is also why I don't have the patience for it either. If you are an EE, I will hold you to a higher standard, and you are currently arguing facts well below that standard.

 

[stickboy1375]

So here I am wondering ........... has any of this helped the OP in the least?

Bob, this thread is so full of information its amazing, it was an awesome read, glad its still going.

 

[Rick Christopherson]

As long as I am on a roll re-addressing information that wasn't worthy of an original reply, let's keep going. If you don't like my condescending replies, then don't try to slip B.S. past me without giving it due thought. Mivey, you are also EE and are also held to the same high standard as any other EE.

There is a darn good reason why your diagram below is drawn the way it is drawn. That's because it is a diagram of two separate transformers connected only by their shared connections. Just because they may share the same can or enclosure does not make them a single transformer, which is what this current discussion is about. You have falsely implied that you are getting different phase angles from different taps on a single transformer, and if you can prove this to be true, then my previous answer stands: I will pay for your patent.

If you can build this transformer from a single core with A-n and B-n primary windings over the top of each other, and then connect it to a 3-phase A-n-B source without the fire department standing by, I'll send you $100. If it was never intended to represent a single transformer, then your only reason for including it in this discussion was to baffle-us-with-B.S. (which is even worse).

Here is a real world example where we make use of the physical reality of the difference in phase:

Open Wye to 4-wire Wye secondary (0? displacement):
.
A----------------)H2..X4(---------------------a..v@0?
.................)......(
.................)......(./\.v@0?
.................)......(
.................)....X3(------------o
........V@0?./\..)...................|
.................)....X2(------------o
.................)......(............|
.................)......(.\/.v@180?..|
.................)......(............|
....o------------)H1..X1(------------|---o
....|................................|...|
....|................................|...|
....|................................|...|
B---|------------)H2..X4(------------|---|----b..v@240?
....|............)......(............|...|
....|............)......(./\.v@240?..|...|
....|............)......(............|...|
....|............)....X3(------------o---|----n..0@0?
....|.V@240?./\..)...................|...|
....|............)....X2(------------|---o
....|............)......(............|
....|............)......(.\/.v@60?...|
....|............)......(............|
N---o------------)H1..X1(------------|--------c..v@120?
....|................................|
...Gnd..............................Gnd

You should be able to plainly see that if the X43 voltage was not really different in phase from the X12 voltage then this would not work in the real world. In fact, it does work and is a common transformer configuration and does not require "magic" transformers.