Ask Me Help Desk - Line to neutral power flow diagram

I find the following excellent link that shows the current flow in a 3 phase circuit:

http://en.wikipedia.org/wiki/Image:3-phase_flow.gif

I am trying to find similar displays that shows current movement in a:
- 220 line to line load.
- 110 line to neutral load.

Has anyone come across them?

You likely won't find animated diagrams for these situations, as they are fairly simple. In house wiring, the two phases are always 180 degrees out of phase. The voltage on any single hot line is roughly a sine wave. If two sine waves are 180 degrees out of phase, while one is going up, the other is going down. Subtract one from the other, and you end up with a sine wave that is twice as high. That's why two 110V hot lines of different phases gives you 220V.

So basically, house wiring can be simplified as a sine wave voltage of either 110V or 220V. Make the other assumption that loads simplify down to resistances, and you can calculate the current using Ohm's law. V=IR holds true for time-dependent voltages and currents as well. V(t) = I(t)*R. The current in a line will also be a sine wave, peaking when the voltage peaks, changing direction when the voltage changes direction. A simple back-and-forth of current is all you would see on an animated diagram.

I always like to use the water pipe analogy to explain 120V line to neutral circuit. The faucet is under pressure, like the hot wire. When the faucet is opened water flows out under pressure, performs some work (maybe turns a water mill) and become depressurized. It then flows out the drain at very low pressure. The drain pipe is like the neutral wire, which carries the current at a very low voltage back to the grounding bus at the main service panel, at which point the voltage is zero.

In a 220V circuit, there is no neutral. I understand that the 2 lines are 180 degrees out of phase and all that, but how do I apply the water pipe analogy? When does the 'spent' electricity go? Where is the 'drain'?

Electricity is quite lazy. It needs a complete path from source to load and back to source. It takes the easiest route- whether 120 or 240V.

Actually 120V is wrong because it is really +120V and -120V. Neutral is 0V and is the same as ground.

So in +120V or -120V line, electricity flows to 0V along the easiest path which is the neutral or ground (hopefully the neutral or your going to get a shock). If the neutral is not connected properly, the electricity will flow through the ground (which is also 0V). The neutral connection provides an easy connection for electricity to flow back to the supply. The ground connection back to the supply requires the electricity to do work. However, even when there is a good neutral connection, electricity will still prefer two connections back to the supply over one. That is why even a healthy neutral connection can give a shock if an electrical device is ungrounded (the electricity will travel through the neutral AND through a person back to the supply because two paths back to the supply are better than one.

On a 240V system, electricity flows from +120V to the load and back to -120V to the supply. No neutral is used but the same shock hazard exists on an ungrounded device. In this case both +120V and -120V will prefer to travel to 0V ground as it is an easier path (it will also give you a larger shock and is more dangerous)!

Quote:

Originally Posted by auondicz

I always like to use the water pipe analogy to explain 120V line to neutral circuit. The faucet is under pressure, like the hot wire. When the faucet is opened water flows out under pressure, performs some work (maybe turns a water mill) and become depressurized. It then flows out the drain at very low pressure. The drain pipe is like the neutral wire, which carries the current at a very low voltage back to the grounding bus at the main service panel, at which point the voltage is zero.

In a 220V circuit, there is no neutral. I understand that the 2 lines are 180 degrees out of phase and all that, but how do I apply the water pipe analogy? When does the 'spent' electricity go? Where is the 'drain'?

Can you explain further the context of your question? I get you like to use the water analogy, but that only works to help explain how electricity "Flows" , and the effect of pressure(volts) and (rate of) flow (current).

I am getting a kick out of some of the new "therory" of electricity I have seen, or more correctly, the perception of electricity and how it works. Once I learn what you are trying to understand or how to use the information, I can help with better explanation than I am about to provide, and diagrams to help illustrate what is going to be difficult to explain here.

Some of the comments made I feel I need to mention and correct:

Single phase is just that, therefore, the "phases" are not 180 deg apart. A single phase circuit is the complete phase, 360 deg.

The confusion comes from the perception of the typical residential 120/240 volt Edison Three wire system everyone has in their homes. The single phase is the 240 volts, the sine wave begins at 0 volts, rises to +240 volts, descends back to 0 V, continues on down to -240 volts, and back to 0. This is a total of 360 deg.

Alternating current changes from 0 to +volts to 0 to - volts to 0 volts, it does this 60 times per second in a 60 cycle system.

The 240 volts comes from a single transformer coil and the voltage does just what I stated above, 60 cycles or times per second.

The 120 volts is nothing but a center tap in the actual center of the 240 volt coil, and the voltage does the same cycle of sine wave, again 60 times per second.

The center tap is the "return" (neutral)for the 120 volt from only one of the hot legs. The neutral is grounded, otherwise there would be two hot legs in a 120 volt outlet. This is done here in North America for safety, so there is only one hot leg at the outlet. If the outlet was not grounded, then both wires would be "hot".

Do you know that Europe uses a 230 volt system, at each outlet, and one leg is grounded! For the same reason, just all their appliances, TV' computers, hair dryers, everything, is rated 230 volts! This is why there is a switch on the back of most personal computers to chose from 115 or 230 volts, so the computer can be sold either here or in Europe.

The ground connection is not for the purpose of requiring the electricity to do work. It is a redundant safety wire attached only to the metal housings of appliances, only to be used in the event the wires inside the appliance come in contact, or "short out' to the metal case. Otherwise the metal case would become live and stay that way until someone comes along and touches it, possibly completing the circuit, and getting shocked.

Electricity is not spent, and there is no drain. One law of physics is that energy cannot be neither created nor destroyed, only transformed into another form of energy. The voltage from one hot leg of a 240 volt system, returns back to the other 240 volt hot leg to form a circuit, and it does go back and forth , (or change from + to -) 120 times due to the 60 cycles.

I think we need to get you to understand the 240 volt portion of this before we go further with the Neutral, which is nothing more than a "shortcut" return for the one leg of a 240 volt system, thus 120 volts. The Neutral is "zero volts" simply because it is grounded, but still is a return.

For the water diagram you are seeking for 240 volts, simply take a hose, connect both ends, cause water to flow in the circle, and there you go. Draw a line at the center diameter connecting the hose at the center points, and there is the neutral.

I felt I had to clear up some of the misconceptions presented here so far, but not sure if I did a good job at explaining it, without confusing you even more. Again, if you can explain exactly what you are seeking ,and more importantly, how the information is to be used, I can provide some better explanations and direct you to some diagrams to show how the current flows, and why.