ECN Forum Forums General Topics of the Trade General Discussion Area How does Electricity flow?

66,

Let me try to answer this with as minimal wording possible, in order to make sense.
If it does make sense, we can elaborate further.

Basic stuff:

Voltage, or Electromotive Force [EMF] is the Pressure that pushes current from point A, through a load, then to point B. It's commonly known as Potential Difference, which is similar to thinking of Potential Energy in science [like a rock suspended in the air above the ground. the rock has potential energy]. The symbolic label for Voltage is "E"

Current, measured in Amperes, is the amount of flowing charges in a closed circuit [one Ampere is figured as 1 coulomb of current flowing across a certain point in one second. A coulomb is the unit for Electrical Charge and is equal to 6.28 X 10 / 18 Electrons, or roughly 628,000,000,000,000,000 Electrons passing one point in one second]. Current flow can be visualized as the way a line of Billiard balls, layed end to end - then struck with the Cue ball at one end, would move. The energy transferes from the cue ball, into the line of balls, then is contained in the last ball, which gets ejected away from the line.

Current flows very similar to this. There is current flowing in both directions at the same time, anytime there is a power source connected [I say this because even if the switches and circuits are open, there is temporary flows - this is beyond the scope of this message! This would be known as Capacitive Charging of the circuits].

Electrons [charged particles on the outer orbits of the Atoms] make up the Electron current flow. Free Electrons in conductors are what the transfer is carried across with.
As Electron current flows from the polarity with the highest accumilation of Electrons [the Negative pole, or position] to the Positive pole, there is an equal transfer of Positive charges brought from the pole with the higher Positive polarity, to the negative pole. This is a typical current flow. All current flows within a closed circuit and through the connected load[s]. The exception is Charging Currents inside and outside the conductor, plus the Magnetic fields on conductors created by current flows [similar to Induction]. The symbolic label for Current [Amperage] is "I"

The combination of Voltage [E] and Amperage [I] flowing through a load, causes work to be done, or Kinetic Energy is released - mostly in the form of heat. This work is measured in Watts, and is the primary unit of Electrical Power. The symbolic label for Wattage is "P" and subscript is "W".
For simplicity, I will not cover Volt-Amperes, or Apparent Power.

If you were to imagine a simple Resistor load - such as an Incandescent Lamp - being powered by an Electrochemical cell [or Battery], the flows and transfers of energy can be explained.

First, place the Resistor in a vertical position, so the leads are up and down. Next, connect the negative pole from the battery to the top lead, and the positive pole to the lower lead. Now think of the Electrons flowing through the load as marbles. Think of the load Resistor as having a restriction that slows them down. Think of the spaces between the marbles as the positive charges.

Place a switch, in the form of some kind of valve that stops the flow of marbles.

First off, with the switch "Open" [no flow], there is a Potential Difference between the top and bottom of the battery [the poles]. The Potential is because the marbles can "fall" downwards, due to gravity. This is how a certain voltage is obtained. It's the Electrostatic Potential Energy between points of opposite polarity.

When the switch is closed [marbles can flow], there still is a Potential difference between the two poles and is now seen at the load's terminals too.
As the marbles move through the load, they transfer energy to the load, in the form of heat. The energy transfer is completed at the end of the load. At this point, the marbles just move because there is someplace to go to, such as a hole and gravity continues to pull them downward. When there is no more area for marbles to flow into, or there are no more marbles available, the flow ceases - and the Potential Difference becomes zero.

[FYI - in Semiconductor Electronics, the Positive Charge carrier is referred to as a "Hole", and the Electron is reffered to as the "Charge"].

Even though this is a semi long explaination, it is extremely brief and explains the most basic flow in a circuit.


The circuit that you quoted has these points:

1: The grounded conductor will have little, to no voltage [potential difference] to ground, because it is at a ground reference - it's intentionally grounded, so it's at, or near, ground potential.

2: Even though the grounded conductor has little to no voltage [potential] to ground, this does not mean it has no voltage! As shown in the basic example above, the potential difference, in Volts, is measured between TWO points of a supply. This means that the total voltage between the ungrounded conductor and the grounded conductor is 120 volts. Voltage is not measured from only one conductor, but is measured between two conductors. This is why a 1 phase 3 wire system has 240 VAC between the outermost transformer taps [the secondary coil's ends] and 120 VAC between either end to the center tapped neutral - it's a 240 VAC transformer with a tap on the winding, making it have 120/240 VAC.

You mentioned that your Ammeter showed X current flowing on the ungrounded and the grounded conductors. This is very common on 3 phase 4 wire Wye systems, when the loads are NOT pure resistive loads [Incandescent lamps, etc.] The common grounded conductor will carry the highest load current. A 1 phase 3 wire system will balance out as much as possible - there are exceptions, but I'll leave this stuff out for now.

I am mentioning this as if the Ammeter was checking circuits at the panel, not directly at the load[s] themselves. At the load, where there is only the two wires connected, you should definitely have equal amperage on both conductors - ungrounded ["Hot"] and grounded ["Neutral"]. If not, there is a connection allowing current to flow into the equipment grounding conductor, which is not correct. This will cause current to split and flow on both conductors.

Now to the power issue!

ExI = P, or in otherwords, The Voltage present at the Load, times the Amperes flowing through the Load, equals the amount of Power that the load is developing and/or drawing from the line. To keep things simple, just figure the Power to be True Power, in Watts - as opposed to Apparent Power, in Volt-Amps [your probably more familiar with KVA - Kilo Volt-Amps].

At 120 VAC, 10 amps flowing will result in 1,200 Watts of power being drawn from the line and developed in the load. 1,200 Watts [or 1.2 KW - Kilo Watts] is being supplied to the load from the Source of Energy [the power company, via the transformer], through the conductors and finally through the Atoms inside the load. This Kinetic Energy that is displaced in the load, will eventually end up as heat, then once again turn back into Potential energy - such as a rain cloud or dust, something that sits around static. This is the conservation of energy.

As stated, if the circuit draws 10 Amperes at a pressure of 120 Volts, the true power consumed by the load is 1,200 watts.
If the Voltage was 240 volts, the same 1,200 watts could be created using only 5 Amps of current. Use the formula ExI=P to see this. The load's Resistance, or Impedance, would have to be a level that will allow a current of 5 amperes to flow when a pressure of 240 volts is applied.

There is no "dead" voltage - only opposite points in Potential. When current flows out of a load, it still has pressure, or Voltage, pushing it. The total Voltage is measured between two points of a power supply.
For instance, the Voltage for a 120/240 VAC 1 phase 3 wire system would be measured at the supply points, which are in reference to the transformer's output. 240 VAC would be measured between the X1 and X2 terminals - which we will say are the outermost ends of the coil. 120 VAC would be measured between either X0 and X1, or X0 and X2 - with X0 being the center tap.

Voltage does not get used up. The total energy that is to be released in the load is what gets "used up". When someone mistakenly connects a load that was meant for a lower voltage [like hooking up 12 volt stuff to 120 volt power], the load burns up, due to the dramatically high amount of Current that can flow through the low Resistance / Impedance, from a higher Voltage pushing it. The combined result is a major increase in the energy developed and released in the load. That's why things fry from overvoltages [once again, there's many exceptions to this stuff, but I am keeping it brief for easier understanding].

I sure hope this, by some means, explains what you were asking me!

I really did keep things down to a bare minimum!! [kind of proud of myself on that one ].

Even though they are minimum explainations, there is still quite a bit to read! If I could by any means reduce the size, I would do it. This should be able to explain with some clarity, the physics of Electrical flow theory.

If I have not answered your question, please let me know your exact situation. Be sure to read through this message fully, as it covers your questions in sections at a time. Might want to re-read it, or print it, then read off line.

I am sure that this message will bring up many more questions, so feel free to ask them.
I would hope that others in thi group, with the knowledge and backgrounds, will jump forth and also include information.

Between others and me, maybe questions can be answered and who knows - it might work out that the person[s] asking for assistance grasp it entirely

That is the desired goal!!!

Good luck!

Scott



[This message has been edited by Scott35 (edited 03-02-2001).]