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So, I've put in or replaced several outlets following wiring instructions online and in the box. Nothing big. I know that if I fail to turn off the breaker then I shouldn't directly touch the black wire, but touching the white wire or the bare copper wire is fine.

From this, I know that the black wire is the supply, power is flowing from it, and will happily flow into me. Since neither the white wire nor the bare copper wire shock me, I don't know the difference between the two, other than "Power flows into these once a circuit is completed" So what is the difference, in detail, between the neutral and the ground connectors in 110V applications?

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    Note that no wire is ever safe to touch without making sure the breakers are off and then you have tested for voltage. Just because the white wire "should be" the neutral, don't trust your life with it. – JPhi1618 Feb 15 '16 at 16:08
  • Lots of good explanations already exist: ab.com/support/abdrives/documentation/techpapers/rfignds.htm – isherwood Feb 15 '16 at 16:15
  • @isherwood, The OP did ask for detail, but many of those "ground vs. neutral" explanations don't really clear up the questions for a typical 120VAC residential application. For instance, the ground and the neutral go back to the same box and are screwed down to electrically bonded terminals, so aren't they the same? What is the difference? Does it really come down to "one has insulation and the other doesn't" or is there more to it? – JPhi1618 Feb 15 '16 at 16:42
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    Feel free to write 'er up. :) – isherwood Feb 15 '16 at 16:44
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Grounding

The bare copper (grounding) conductor is a safety system that provides an effective ground-fault current path, and should only ever have current it in the event of a fault. It provides a low resistance path back to the source, so that a fault can be cleared by the breaker (trip).

Grounded (neutral)

The grounded (neutral) conductor is a current carrying conductor, and is used to complete the circuit back to the source. In normal use, it will carry the same amount of current as the ungrounded (hot) conductor.

Touching this wire is not recommended, as there is actually current flowing through it. However, as it likely provides a lower resistance path back to the source, most of the current will flow through the wire instead of you. If there's enough current flowing, or you provide a good enough path to the source, touching this wire can result in large amounts of current flowing through you.

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  • I mean, you basically said it, but you didn't SAY it. The grounding wire is a completely different size going back to the service. Where the neutral wire will be the same size as the supply, or double rated for a 220 two leg residential service, the grounding conductor can be much smaller. Also of note, grounding wires are occasionally insulated - but its not required and is cheaper for them to be bare. – Sean Boddy Feb 15 '16 at 21:41
  • @SeanBoddy The grounding conductor may be smaller than the ungrounded (hot) conductors, but it's always sized large enough to handle the fault current. Also, the grounding conductor doesn't typically go all the way back to the service. The service neutral usually carries the fault current from the service equipment, back to the service. Lastly, the neutral is not double rated. It's the same size as each ungrounded conductor, since it only ever carries the unbalanced load. – Tester101 Feb 15 '16 at 23:07
  • You're thinking 3 phase. Houses in North America get 220 from a transformer equipped with a double rated center tap neutral, because almost all of the load is "unbalanced" - top to center or bottom to center. – Sean Boddy Feb 15 '16 at 23:33
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    @SeanBoddy No sir. In a 120/240V single split-phase system, the center tapped neutral only carries the unbalanced load. If L1 and L2 are each carrying 50 amperes, the neutral is carrying 0 amperes. – Tester101 Feb 15 '16 at 23:36
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The Ground wire is purely for safety, and carries no current during normal use.

The Neutral wire is responsible for carrying all the "return" current the Hot wire provides to the electrical device.

The neutral wire is not, however, a perfect conductor, and has some resistance. A 100 foot run of 14 awg wire, for instance, has 0.25Ω resistance. If an electrical device is using the full 15 amps maximum load allowed on that wire, then at that load the neutral line will be a little more than 3 volts away from ground.

3 volts AC isn't a lot, but it can be noticeable if you happen to touch it, and under some circumstances it can be fatal. Further, without ground, it's one failure point away from having a full 120V available on it. For instance, if it's at the end of the circuit and has a number of daisy chained outlets in the path, the resistance goes up significantly, increasing the voltage level under load, and increasing the chances of a poor arcing connection at one of those locations.

It's the reason why ungrounded equipment (two prong plugs) is designed to be fully insulated from the user - even though neutral is near ground, it isn't ground and depending on the connection quality along the way to the panel and the load on the line, it may be dangerously far from ground.

If you place a highly reactive load at the end of the line (motor, switching power supply, etc) that uses the full current capacity of the line (you'll notice that these types of loads are almost always grounded) then you'll find that the neutral line is carrying a waveform that may be far from safe, even though, technically, it's a very low RMS AC voltage.

Never, ever treat the neutral line as safe.

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I will try to answer your question but we have to correct and understand some details.

First, touching the white wire is not always fine. In fact, it can deliver quite the shock, even more so than the black wire alone. Why is this you may ask? Well, the black wire is the supply, but keep in mind that all a circuit is is a loop. Black and white are just colors to help keep the logical flow going. The logical flow is either parallel, and or series circuit, or both together.

The most fundamental circuit is always a series circuit. The white wire in most cases is the last stop in the loop to finish the circuit. And depending where the loop is broken will determine the amount of voltage and ampacity.

The black wire is usually ran in a parallel which means it will always have its full potential available. This is often not the case for the white wire where the voltage potential is depleted. This depletion gives the illusion that it is not dangerous because it will not trip a breaker, or cause a explosive arc when connected to a ground. However, if you by accident become part of the circuit loop, you will definitely feel the shock.

The entire reason behind a grounding system is simply REFERENCE. Without a ground, there is no reference to zero voltage potential. Why is this so important? Think of it similar to Greenwich Time. Why do we use GMT in the first place? It serves as a starting point. In the electrical industry, the reference is used for safety as many have already pointed out, but there are many other uses such as for antennas, system calibrations, surges, and so on.

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