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Old 02-24-2008, 01:19 PM   #1
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Neutral vs ground


What's the difference between neutral vs. ground, I am rewiring my air compressor to run on 220v and the question of what to do with the white wire has arised, as I wished to use the circuit for the stove. I have figured this out with the help of this board(many thanks) , but I guess I am still confused in theory about the differences between the neutral and ground. Do they not both provide a return path for the electricity?


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Old 02-24-2008, 01:24 PM   #2
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Neutral vs ground


A Neutral represents a reference point within an electrical distribution system. Conductors connected to this reference point (Neutral) should, normally, be non current carrying conductors, sized to handle momentary faults (short circuits) occurring in electrical equipment.





A Ground represents an electrical path, normally designed to carry fault current when a insulation breakdown occurs within electrical equipment.

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Old 02-24-2008, 01:36 PM   #3
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Neutral vs ground


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Look at your wires in the branch circuit where you are wiring to the compressor. You have 3.
Black = ungrounded conductor coming from the breaker.
White = grounded leg (neutral) connects back at the breaker panel to the neutral bar.
Bare or green = the equipment ground also connected back at the panel to the neutral bar. (ground bar if it is a sub-panel) It never connects to the neutral until it gets to the service equipment where the main disconnect to the dwelling is located.

Key difference between the two is that the neutral is a current carrying wire providing for the return to the center tap of the transformer to complete the electrical circuit. It is only needed for 120 volt loads. 240 volt loads require no neutral.

Equipment ground is a non current carrying wire and only carries current in the event of a ground fault. This fault current then travels that equipment ground back to neutral bar in the panel. Then goes to the center tap of the transformer. This low impedance path allows enough current to flow thru the breaker to cause it to open and de-energize the circuit. So the equipment ground or ground as you are calling it is for human safety and has nothing to do with the electrical system operating correctly. It keeps you from getting shocked or worse.

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Old 02-24-2008, 02:22 PM   #4
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Neutral vs ground


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Originally Posted by chris75 View Post
A Neutral represents a reference point within an electrical distribution system. Conductors connected to this reference point (Neutral) should, normally, be non current carrying conductors, sized to handle momentary faults (short circuits) occurring in electrical equipment.
What?

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Old 02-24-2008, 02:56 PM   #5
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Neutral vs ground


See if this helps you see the difference between the two. The neutral of a 120 volt branch circuit or grounded leg (grounded because it bonds with the service neutral) is carrying the current of the branch circuit.

The equipment grounding conductors shown in green carries no current unless a ground fault occurs on the branch circuit. An example would be a hot wire coming loose in a wirenut and touching the bare equipment ground wire or contacting the metal box the equipment ground might be connected to. Notice the green wires in the diagram go back to the neutral bar in the panel where they bond with the service neutral. In the event of a fault this low impedance path back to the neutral bar then out the service neutral to the transformer center tap allows a breaker to trip.

The diagram essentially shows a 120/240 volt circuit like would go to your electric dryer.... load #2 would be your heating element (240 volts) and load # 1 would be your dryers motor and buzzer (120 volts). Separating the two out into individual branch circuits I think you can visualize.
Attached Thumbnails
Neutral vs ground-120-vs-240-volt.jpg  

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Old 02-24-2008, 03:45 PM   #6
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Neutral vs ground


Quote:
Originally Posted by chris75 View Post
A Neutral represents a reference point within an electrical distribution system. Conductors connected to this reference point (Neutral) should, normally, be non current carrying conductors, sized to handle momentary faults (short circuits) occurring in electrical equipment.

.
as inphase277 said: what???

get rid of this absolutely incorrect and possibly dangerous advice.

A neutral is a current carrying conductor normally. The only time it does not carry current is when it is used in a multi-wire branch circuit where the two circuits are carrying EXACTLY the same amount of current. Well, the other time is when the circuits are not being used.
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Old 02-24-2008, 04:05 PM   #7
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Neutral vs ground


Chris

I believe I understand what your saying but the language you used would qualify you for a position on a code making panel.......

Remember this is a DIY site and that explanation would have given me a huge headache if I was a homeowner.....and appears to have given one to a few of our fellow electricians
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Old 02-24-2008, 05:06 PM   #8
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Neutral vs ground


The neutral normally carrys current. The ground doesn't.


The ground bonds metal components to the neutral at the point of origin (service) as a safety precaution.

If a metal component were to come in contact with a hot wire it will cause the breaker (fuse) to disconnect. If it is not "grounded" it will become energized.

Last edited by 220/221; 02-24-2008 at 05:30 PM.
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Old 02-24-2008, 05:13 PM   #9
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Neutral vs ground


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Originally Posted by Stubbie View Post
Chris

I believe I understand what your saying but the language you used would qualify you for a position on a code making panel.......

Remember this is a DIY site and that explanation would have given me a huge headache if I was a homeowner.....and appears to have given one to a few of our fellow electricians

Opps. my mistake, I posted what a neutral was, I dont call grounded conductors neutrals...

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Old 02-24-2008, 05:18 PM   #10
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Neutral vs ground


You know it just dawned on my dense head I should be that last person to ***** about confusing posts...

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Old 02-24-2008, 06:03 PM   #11
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Neutral vs ground


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Originally Posted by chris75 View Post
Opps. my mistake, I posted what a neutral was, I dont call grounded conductors neutrals...
Well, the OP asked about grounds and neutrals. Due to the typical layperson and the terminology they would use and realizing this is a DIY site that the typical person asking questions is a relatively non-trained person, we, as trained individuals should take that into consideration and read into the question to see it from the perspective of the layperson poster.

(how is that for a run on sentence?)

So, due to that, the question was quite clear while your answer, I presume, was meant to be from the perspective of the engineering/theory point of view.

They won't get it and it does tend to confuse them as it appears to the untrained person that you have answered the question incorrectly. That is why I did state you were incorrect while I do understand and acknowledge what you were saying.

When speaking to a 3 year old (not inferring our posters fit that bill), you speak as a 3 year old. Communication is the art of transferring thoughts, ideas, and information to another. You cannot communicate unless you speak in commonly accepted and known terms.


Never mind. Ignore all the above/

quit plagiarizing without credit Chris75

http://www.ab.com/drives/techpapers/rfignds.htm

That mistake makes you look like you have no idea as to what you speak of.
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Old 02-24-2008, 06:04 PM   #12
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Neutral vs ground


Quote:
Originally Posted by 220/221 View Post
The neutral normally carrys current. The ground doesn't.


The ground bonds metal components to the neutral at the point of origin (service) as a safety precaution.

If a metal component were to come in contact with a hot wire it will cause the breaker (fuse) to disconnect. If it is not "grounded" it will become energized.
Question: What exactly is happening with the breaker when the hot touches something? Example: Screwdriver in the slot of a receptacle.

Quote:
Originally Posted by Stubbie View Post
See if this helps you see the difference between the two. The neutral of a 120 volt branch circuit or grounded leg (grounded because it bonds with the service neutral) is carrying the current of the branch circuit.

The equipment grounding conductors shown in green carries no current unless a ground fault occurs on the branch circuit. An example would be a hot wire coming loose in a wirenut and touching the bare equipment ground wire or contacting the metal box the equipment ground might be connected to. Notice the green wires in the diagram go back to the neutral bar in the panel where they bond with the service neutral. In the event of a fault this low impedance path back to the neutral bar then out the service neutral to the transformer center tap allows a breaker to trip.

The diagram essentially shows a 120/240 volt circuit like would go to your electric dryer.... load #2 would be your heating element (240 volts) and load # 1 would be your dryers motor and buzzer (120 volts). Separating the two out into individual branch circuits I think you can visualize.
Your drawing has the black from the transformer labeled +120 and the red labeled -120. Is there any significance?
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Old 02-24-2008, 07:32 PM   #13
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Neutral vs ground


Quote:
Originally Posted by CowboyAndy View Post
Question: What exactly is happening with the breaker when the hot touches something? Example: Screwdriver in the slot of a receptacle.
A huge current flows because there is practically no resistance. This causes the breaker to trip because of the large electromagnetic field caused by that. The breaker is held closed by a catch that gets pulled out by the magnetic effect.



Your drawing has the black from the transformer labeled +120 and the red labeled -120. Is there any significance?[/quote]

This is more like a snapshot of an instant in time. At any give moment, one leg is + and the other is -. They alternate every 1/120th of a second.

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Old 02-24-2008, 08:03 PM   #14
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Neutral vs ground


Yes it simply is showing that the 240 volts has opposite legs... one pushing and one leg pulling the current through load #2 at the same time. So if that load was 20 amps I would have 10 amps entering one end of the load and 10 amps entering the other end all at the same time. In contrast if the 120 volt circuit was a 20 amp load I would have 20 amps entering the top and when the current switched directions 20 amps entering from the bottom. So the 240 volt is a 2 lane highway circuit and the 120 volt load is a one way street. Remember alternating current changes direction 120 times a second. The arrows show this change of direction that Inphase has mentioned.

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Old 02-24-2008, 08:44 PM   #15
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Neutral vs ground


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Originally Posted by Stubbie View Post
Yes it simply is showing that the 240 volts has opposite legs... one pushing and one leg pulling the current through load #2 at the same time. So if that load was 20 amps I would have 10 amps entering one end of the load and 10 amps entering the other end all at the same time. In contrast if the 120 volt circuit was a 20 amp load I would have 20 amps entering the top and when the current switched directions 20 amps entering from the bottom. So the 240 volt is a 2 lane highway circuit and the 120 volt load is a one way street. Remember alternating current changes direction 120 times a second. The arrows show this change of direction that Inphase has mentioned.
You sure about that Stubbie?

I have to disagree with ya here. Regardless of the voltage, if it is a 20 amp load, you always have 20 amps flow on either/both legs. A single phase system only hase one sine wave whether it is 120 or 240 votls. You do not get more voltage because of some additive of multiple sine waves or anything, it is simply a result of the ratio of windings. If your description were correct, you could use smaller wire AND breaker for a 240 volt circtuir. The only reason you can use a smaller 240 volt circuit is Ohms law says you will NEED less current to produce the same amount of power.

Now, to the 120 volt being a one way. again, I must disagree with that. There is exaclty the same action with a 120 volt circuit as there is wiht a 240 volt circuit. The neutral (grounded conductor) serves the same purpose as the second leg of the 240 only due to the winds ratio, only 120 volts is supplied. The only reason you read 0 volts to ground is that the neut is tied directly to ground. IF you could remove the POCO's neutral-ground bond and your neut-ground bond you could actually ground on of the typically hot legs. You would have 120 to the center tap and 240 to the other leg but you would have 0 to ground on that leg and the other normally hot leg would read 240 to ground.

If you scoped the 120 and the 240 volt supplies, they would lay over each other other than the 240 would obviously peak higher (and lower) due to the higher voltage.

Please correct me if I am wrong.

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