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# AC and DC Circuits

#1
04-26-12, 07:49 PM
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AC and DC Circuits

I read some basic electrical theory and it didn't really explain what I was hoping to see, so I hope maybe I can get some help here.

In a 120 volt electrical lighting outlet, the hot wire feeds power to the component that produces the light, then the neutral carries the current out of the component.

Now that is an alternating current outlet, but because of the nature of the electrons it seems to be more of a direct current circuit. What am I missing?

On a 240 volt appliance outlet there are two hot wires and no neutral. Is it the 'out of phase' that alternates the current back and forth from lead to lead out of the circuit?

Thank you in advance for any replies and explanaions!

#2
04-26-12, 08:06 PM
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Now that is an alternating current outlet, but because of the nature of the electrons it seems to be more of a direct current circuit. What am I missing?
That it doesn't always flow in on the hot and out on the neutral. Sixty times a second it changes direction coming in on neutral and leaving on the hot.

On a 240 volt appliance outlet there are two hot wires and no neutral. Is it the 'out of phase' that alternates the current back and forth from lead to lead out of the circuit?
Correct, just like 120v.

#3
04-26-12, 08:28 PM
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Is 'neutral' just another 'hot' wire that goes back to the transformer? Does the red wire (main hot wire) just go back to the panel?

#4
04-26-12, 08:43 PM
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Is 'neutral' just another 'hot' wire that goes back to the transformer?
Yes, it is the grounded center tap off the secondary of the supplying transformer.

Does the red wire (main hot wire) just go back to the panel?
All wires go back to the secondary of the supply transformer.

#5
04-26-12, 08:45 PM
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In that case I'm not seeing the relevant difference between the two wires besides the name, lol!

#6
04-26-12, 10:38 PM
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Neutral is the grounded conductor. It comes from the center tap of the transformer.

#7
04-27-12, 05:04 AM
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120-volt AC power has one goal: To get to earth ground. The neutral is bonded to building ground inside the panel in your home. The connection between hot and earth can happen anywhere there is a potential for the electricity to pass to ground, including through humans. More commonly -- and safely -- it is a ground rod or water pipe.

DC power is a closed system that doesn't technically use a ground. Instead, loads are connected to a closed loop that uses a "zero volt reference" relative to the +VDC or -VDC that originates at the power source.

#8
05-01-12, 04:10 PM
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The actual destination of the neutral current in a home is the transformer where the corresponding hot line came from.

The neutral conductor accompanies the hot conductor(s) up from the panel and out to the utility pole transformer. Household current can use the ground (earth) for a return because both the home and the utility pole have wires from the neutral line down to a ground rod or other buried metal object. In practice only a few amperes can flow this way before voltage drop losses become too great causing lights to dim, etc.

So the household electrical system is also a closed loop, from the pole transformer secondary and back. The neutral is the "zero volt reference".

The distribution circuit (primary line, nowadays typically in the 7500 volt hot to ground range) is also a closed loop, from the substation to the pole transformer.

#9
05-01-12, 07:07 PM
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Allen hit the nail on the head posting that current tries to get back to the source any way it can. It does not matter if it is a 120v circuit, 240v circuit, or any other voltage it all reacts the same.

Electricity is commonly compared to water in a pipe, which is a good analogy, but there is a big difference. The water in a pipe flows in one direction. This is more like a DC circuit.

In an AC circuit, the water would flow in one direction, come to a stop, then move in the other direction, come to a stop again and reverse direction again. The alternating happens 60 times a second.

Some light reading: Alternating current - Wikipedia, the free encyclopedia

Here is another fun one: Electricity is never consumed. It is only the movement of electrons that provides work. The electrons are always present in the wire.

#10
11-20-12, 08:10 AM
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AC vs DC

I think you will find some extensive knowledge on this topic at this link I came across
AC vs. DC Power - How it affects power system design | Power Systems Engineering

It gives a good comparison between each of those and lists their advantages and disadvantages. Take a look. It could be of good help.

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