ECN Forum Forums General Topics of the Trade General Discussion Area What are Non-'Line to neutral' loads?

Bob-

Thanks. To clarify...
For AC power, + and - are alternating. Books and professor types always show the sine wave to demonstrate this. But at the microscopic level, is the alternation happening on the X axis or Y axis?
To paraphrase, for one complete AC cycle, is the current A) moving back and forth along the length of the conductor from source to load
B) rising and falling up and down across the wire
C) Something I haven''t though of yet.

None of my test prep books go very deep into this and I'd prefer to understand it instead of accepting and memorizing it.

Thx

Wow now we are going deeply
over my head.

There really is no plus or
minus in AC it swaps back and
forth.

The best way it has been explained
to me is this.

Imagine a tube (the conductor) filled
with a single row of ping pong balls
(the electrons), this tube could span
the entire country but as soon as you
push a new ball in one end, a ball pops
out the other end, now reverse this 60
times a second and you might have a picture
in your mind of what is going on.

One single electron may not really move
much it just pushes the one beside it.

But like I said, getting this deep is
really beyond me, you should wait for
some more responses before committing the
ping pong balls to memory.

Bob


[This message has been edited by iwire (edited 04-20-2004).]

[This message has been edited by iwire (edited 04-21-2004).]

I think I have it now.

Except for one thing. Do you score a point in ping pong if it's not your serve?


Seriously, Thanks for helping.

Haligan;

The best and simplest answer I can give or explain to you for:

"What Are Non-Line-To-Noodle (Neutral / Grounded Conductor) Loads"

Would be this:

"Any Circuit / Load Which Does Not Use The Grounded System Conductor"

L-L (Line-to-Line) and / or 3Ø L-L-L (Line-to-Line-to-Line) Circuits + Connections to Equipment do not use a Grounded Conductor for their Circuitry.

Most commonly known types of these loads would be 1Ø Air Conditioners, Electric Water Heaters and 3Ø Induction Motors.
These loads would have Branch Circuits deriving from 2 or 3 Pole Circuit Breakers.

As already mentioned, the "Typical" L-L Voltages (U.S. Systems) would be:
208, 230 (240), 460 (480) and 575 (600).
This is not 100% default though, as a "Single Voltage" rated system - and even a Multiwire type System, may have these voltages between an Ungrounded Conductor and a Grounded Conductor.
The key on the "Single Voltage" rated systems is the Grounded Conductor is not the typical "Noodle" (Neutral / Common Conductor).

For a 3Ø 3 Wire Grounded Delta, there is a Grounded Conductor, but it's not a "Neutral".
The Voltage between any two conductors will be (close to) the same no matter which 2 Lines are measured.
For instance, if the system was 240 VAC, there will be 240 VAC between any two wires - even the one which is Grounded and any of the remaining two Ungrounded Conductors.
Voltage to Ground will be 240 Volts from any of the two Ungrounded Conductors, and ZERO from the Grounded Conductor and Ground.

An example: If we Grounded Ø Line "C" at the Transformer + the Service, ØA and ØB will show 240 VAC to Ground, but ØC will show ZERO Volts to Ground.
Measuring between A-B, B-C or A-C will show 240 VAC.

The exception to the L-N / L-L reading would be what's found on the 120/240V 3Ø 4 Wire Delta.
The system will have a nominal L-L Voltage of 240 VAC from A-B, B-C and A-C.
The winding forming "A-C" at the Transformer, is Center Tapped - which results in a Voltage of 120 VAC from Line A and Line C to the Center Tapped Grounded Neutral Conductor / Ground.
From Line B, the Voltage to the Center Tapped Grounded Neutral Conductor / Ground is around 208 VAC.

There are a lot more varieties of systems which differ greatly from "The Common Ones", which may be discussed in detail if needed.
Check out the Electrical Theory and Applications area for past threads covering these items. Also check through the Technical Reference section for various Scematics of Transformers + etc.

Bob (Iwire) has done very well with the information He has posted in this thread!

Allright Bob!!!

To try and assist a bit on the "+/-" and "Returning Current" subjects of AC, refer to the Transformer Schematics shown in one of Bob's (Iwire) posts.

First thing - do not even worry about anything being Grounded! Consider all these Transformers to have absolutely no physical connection to "Ground" at any point.
The Inputs (Primaries) and Outputs (Secondaries) will not be Physically Connected To the Earth Ground anywhere.
This eliminates the "Ground Return" consept all together - and helps make the most important points about the normal operation of an AC Power System.

With the above stuff in mind, visualize the Current Flow on each side of the Transformer - Primary Windings and Secondary Windings.

Visualize the Current flowing acrossed each Winding as if it was moving like the Blade of a Sawzall (Reciprocating Saw).
Picture it going back and forth, keeping a constant "Frequency" time speed, yet "Peaking" at the "End" of a certain direction's movement (as the Blade reverses direction and moves the other way).
Picture this continuing over and over and over - like two Kids on a "See-Saw", when one Kid goes up, the other goes down. The Kid that went down pushes up off the ground, causing the "Up" Kid to come down, reversing the directions of movement for the two Kids.
If they don't get tired (or bored), they will continue to "Alternate" their positions between "Up" and "Down" - yet they are still the same Kids, on the same Teetering Board, with the same Fulcrum Point at the Center of this "Lever" - the Teetering Board.

That is what simply is going on with the Current on an AC Circuit - the Current 'Runs" in one direction, then "Runs" in the other direction.
There is no fixed Polarity (only "Transient Polarity Points or Reference Points) - just like the Sawzall Blade and the Kids on the See-Saw.

This simple theory may be applied to any of the Transformer Schematics shown in this thread, and to any of the Windings (Primary or Secondary) - regardless if there's 2 or 3 wires from the coil.
It's that simple!!!

For more information, check the Electrical Theory / Applications section, and the Technical References section here at ECN.
Also feel free to ask any additional questions you may have.

Scott35

Scott35-

I really appreciate the time it took you to explain that.
The L-L, L-L-L, L-N is clear now and I feel as though I could explain it to my Mom.
(one of my old professors used that as a way to figure out if you really understood something. Maybe he was sexist.)

Now for my final gaps in grasping the 'grounded conductor'.
Another shortcoming of the electrical books I've seen is that they all start to get a little gray once you get out to the utility transformer. You said that they aren't connected to ground. I know that the groundING conductor is unrelated to transformer operation. But, for the groundED conductor to get it's name. That I'm going to read up on to fully understand. I'm overthinking it.

So there's the sawzall/ping-pong balls alternating direction with RMS, Peak to peak and all that good stuff.
The blade/balls are moving along the conductor, alternating + -, back and forth. Now, using Bob's pingpong analogy, at 90deg (+) there is a ball popping out on the 'other' side, moving away from the transformer.
Here's the question-
Does that ball go all the way through the hot, and continue through grounded cond. and pop out on the transformer side in a loop?
OR
At 270deg (-) is it popping back out back on the conductor it originated on? If so, what is happening on the grounded cond? I'm trying to apply the answer of this question to Kirchoff's 2nd law about opposite loads cancelling in the neutral. Something strange is happening to the ping pong balls there. It may be too early to introduce this into the equation.

I will start browsing the Theory archives today before coming back with additional questions.

Thanks again, I am very grateful.

Just found an answer to big question in the Theory forum.
There is a good white paper from APC about the neutral.

It's not quite a loop-- but the electrons travel back and forth through hot conductor, the actual load itself, and the 'neutral' whether it be L-N or L-L.
What kept screwing me up was thinking that there had to be some potential difference eg. 120v to zero at the ground, for electrons to move. I have thoroughly purged that from my head. Where did that come from? Whoa!

Bob's poetic statement about neutral not needing to be grounded now makes sense. One point the APC article doesn't make is with the alternating +/- on the 'neutral' in the case of L-N loads-- where does the current on the noodle terminate. At the panel it goes to building ground. But couldn't it also go through the meter up to the transformer?

By the way, if you feel like I'm not making progress here, please tell me to go to "H-E-double-two-sticks". I'll understand. :-)