Hi,

I was wondering if I could get some help understanding 2 and 3 pole circuits. For whatever reason I have had trouble understanding the theory behind the electron flow with them.

I understand that electrons are always trying to go back to the source. With 120V single pole circuits they flow through the hot, through the load, and back on the grounded conductor.

I understand that in a 2 or 3 pole circuit with a neutral, the unbalanced load is carried back on the neutral.

Here are my questions:

On a 2 pole or 3 pole circuit that say does not have a neutral or has a balanced load, how do the electrons get back to the source? Do I understand right that they flow through the load 180 degrees, or 90 degrees in 3 pole circuits, out of phase from each other and return to the source through the other hot conductor? And with AC current the electrons are moving in both directions, correct? Back and forth, back and forth, back and forth. ...

Thanks for your help. I feel like I have a bit of a gap in understanding this concept.

For a basic understanding of 240/120V split phase, I think that an analogy with DC and batteries can help.

Imagine two AA batteries with the negative of one connected to the positive of the other, and wires connected at both ends and in the middle. Like this:

*[+1.5V-]*[+1.5V-]*

The asterisks (*) represent wires you can connect loads to.

You can connect a 1.5V load to either outside wire and the middle wire, but the middle wire is positive for one set and negative for the other. You can connect a 3V load only to the outside wires.

If you have two identical (i.e. 'balanced') 1.5V loads connected to each side at the same time, that is the same as a single 3V load, and the middle wire is not necessary. If you understand Ohm's law you can run the formulas for each load separately or both loads together and see that the current is the same in all situations. When both loads are connected, no current flows on the middle wire; you can think of it as canceling out, or just you've turned the loads into a 3V load. But if you want to control the two loads separately then you need the middle wire.

Now to convert the analogy to AC, imagine a little magic elf flipping the batteries around 120times a second. :thumbsup::lol: The important thing to understand is that if your loads are not polarity sensitive, then the mathematical relationship is the same (i.e. mirror image) with the batteries flipped around. This is true even with a real AC sine wave that varies the voltage.

A split-phase transformer is just two windings stuck together exactly the same as the batteries, except that being AC the outside terminals are not designated negative and positive. But imagine them as having one polarity half the time and the other polarity the other half the time, courtesy of the elf.

This will help you understand which direction current flows during either half of the AC cycle.

This analogy is not so immediately useful with 3-phase, but if it can help you fully wrap your head around split phase then you're on your way to understanding 3 phase too.