Alternating Current: neutral & ground

  • #1

Main Question or Discussion Point

I'm having a difficult time understanding precisely how alternating current works in relationship to ground (earth). I have spent hours trying to learn online and I get conflicting explanations.

So lets start with a power plant. A coil of wire is rotated in between magnets, inducing a voltage. Does the generator have to be connected to ground for there to be a potential difference, or is their a difference and hence a voltage independent of earth?

Either way, the hot wires enter a home and power various loads. The neutral wire leaves these loads, and the voltage potential to ground is ideally zero or near zero. Would this not happen if the neutral and ground were not bonded at the main panel of a house? If alternating current switches direction back and forth, but neutral has a zero voltage, then how can it do work when the current is traveling from neutral to hot?

In other words, besides our optional but wise use of ground for fault safety, is it required as a zero reference, or would there still be a voltage potential between hot and neutral in our electrical system never contacted ground?
 

Answers and Replies

  • #3
meBigGuy
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BTW, I summarized it for a 60 amp 240VAV main with neutral as (neglecting power factor):

Again I learn something I thought I knew (thanks for that). The 60 amp service can supply 60 amps on either or both legs. The neutral conducts up to 60 amps as required by mismatched loads. If the loads are matched it conducts zero (since the matched loads are a perfect voltage divider and the middle point is 0V). Cool.
 
  • #4
jim hardy
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Most folks start out confused about "ground", probably because of early imprinting.
We see lightning bolts go to the ground, and we see our Dad make sparks when the lamp he's fixing shorts out, so we come to believe electricity has some curious affinity for the ground.


In other words, besides our optional but wise use of ground for fault safety, is it required as a zero reference, or would there still be a voltage potential between hot and neutral in our electrical system never contacted ground?
The question is asked here often.
And you already know the answer:
Does a flashlight work okay with no connection to earth?
Does the DC power system in your automobile work okay? It is insulated from earth(ground) by the tires.
Does the AC power system in an airplane or the space station work okay with no connection to earth?


A 120 volt household generator from Home Depot would work just fine on the moon were there any air to run the engine ...


"Earth ground" is just another wire that happens to go most everywhere.

Remember - voltage is potential difference, not just potential.

Here's another thread or two on the subject:

https://www.physicsforums.com/showthread.php?t=526008

https://www.physicsforums.com/showthread.php?t=506179&
 

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