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I'm learning about electrical engineering and I'm confused about the difference between ground and neutral line. What's different between them?

Ok, I've edited this question for everyone can understand why i'm being confused.

I have an Arduino board here and there is a pin called "GND", as i understand GND is stand for "Ground". . So there are 3 different concept that i need to learn : "Ground", "Earth", "AV Neutral" ?

So what is the voltage output of that GND pin ? Is it 0v ? What is the voltage output of "Earth" ? What is the voltage output of "AV Neutral" ?

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Wuthian
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    Huh? What is "mass 0V"? – Olin Lathrop Jul 18 '13 at 12:13
  • @OlinLathrop i mean if i have a battery that have one direction is +5v and one direction is 0V . So can i call the 0v direction is mass 0v ? – Wuthian Jul 18 '13 at 13:31
  • What exactly are you referring to? Do you mean: ground = PE, mass 0V = reference potential of a circuit, neutral line = AC neutral? – Rev Jul 18 '13 at 13:57
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    Is *mass* something you are translating from another language? I'm not sure that word has the same meaning in English, in an electrical context. – Phil Frost Jul 18 '13 at 15:31
  • possible duplicate of [What is ground and what does it do?](http://electronics.stackexchange.com/questions/56210/what-is-ground-and-what-does-it-do) – Phil Frost Jul 18 '13 at 15:41
  • Never heard "mass" used as an electrical ground. The English word "mass" is very fundamental in Physics. It refers to the extent to which a free body resists acceleration when a force is applied, and the extent to which a free body is pulled by some uniform gravitational field of a given strength. – Kaz Jul 18 '13 at 16:05
  • I have heard this term "mass" before, it is synonym for GROUND, but it is used in non-english speakers, and even then it is wrong word to use. Probably origin of the term came from something that is connected to the mass of the earth, or something similar. – zzz Jul 18 '13 at 18:36
  • @kaz: "Masse" is a very common German term that is more or less equivalent to the English use of "Ground". Translating it to "mass" in an electronic sense is obviously wrong but happens often because "mass" as the a property of a physical body also is called "Masse" in German. – Rev Jul 18 '13 at 19:46
  • @rev1.0 Does the electrical system in a German airplane have a "Masse" network, or does Masse have to be an actual earth? – Kaz Jul 18 '13 at 19:49
  • @Kaz: Yes, it is also used to name the reference potential if it is not connected to earth. "I connected Ground of my circuit to Earth" would mean the same as "I connected Masse of my circuit to Earth". Most German engineers would call it Ground anyway because everyday work (data sheets) is based on all those English terms. – Rev Jul 18 '13 at 20:03

1 Answers1

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So what is the voltage output of that GND pin ? Is it 0v ?

'GND' is the circuit common, the datum, the reference node, or more colloquially, it's the node where you put the black lead of your voltmeter.

In other words, it is the node to which all other node voltages in the circuit are referenced.

It is not a voltage output. The 'GND' pin does not output 0V.

Think about it. If you want to measure the voltage on the 'GND' pin, you would put the red lead of your voltmeter on that pin. Where is the black lead connected? It's connected to the very same pin. So, with both leads of the voltmeter connected together, you read 0V.

When you connect a 5V power supply, the 5V is the voltage across the two power supply leads. When you connect the more negative lead to the 'GND' pin, and the more positive lead to the '5V' pin, you're placing 5V across those two points in the circuit.

Similarly for the 3.3V power supply.

It is often the case that we need two (or more) isolated reference nodes, i.e., 'GND1' and 'GND2' or perhaps "digital ground" and "analog ground". Sometimes, this is for safety, and other times, this is for, e.g., isolation of noise so to reduce interaction between sub-circuits.

And what is the different between GND and Earth ?

The 'GND' node in a circuit is just like any other node. It just that it is, by convention, the 0V node.

'Earth', on the other hand, is an actual physical connection to the Earth via, for example, a long copper rod driven several feet into the soil.

"Earthing" is important in, for example, radio transmission where one lead of the transmitter is attached to an antenna and the other is connected to the Earth.

There's much more that can be said about this but it may be more than you want to know.

To emphasize the essential arbitrariness of the GND node, consider two circuits identical in every way except for the arbitrary choice of the reference or GND node. The voltage across and the current through each circuit element are unchanged by this choice as can be verified by KVL, KCL and Ohm's Law.

The changing of the reference node is no different from changing the location of the reference lead of your voltmeter.

If you place the reference lead between the two voltage sources, the voltmeter will read the following node voltages:

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If you place the reference lead on the negative end of the bottom voltage source, the voltmeter will read the following node voltages:

enter image description here

Again, the circuit operation has not changed. Changing the location of the reference lead of your voltmeter will not change the operation of the circuit. But, it will change the readings you get!

Alfred Centauri
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