Can anyone tell me what is the real difference between neutral wire vs ground besides their phical differences? Is it correct that the neutral wire connected to the wire in the electrical panel which goes into the ground and the neutral connect to the neutral to the street pole? Since they have voltage difference = 0, are they interchangable in practice?

Thanks
Paul Lee

The ground aka equipment grounding conductor normally does not carry current. The neutral aka grounded conductor (did I get that name right) normally is the current carrying conductor that returns the current feeding a load from a hot wire. Both ground and neutral are at 0V, but the two are connected together at only one place, usually the service equipment. It's done as a fail safe thing, if the current carrying neutral was also the grounding conductor, and if a connection in the neutral open up (like a bad wire nut connection) then equipment that was grounded to the neutral downstream of the bad neutral connection would become "hot" thru the load on the hot wire. That's 120VAC on the frame of a window air conditioner, an obvious shock hazard. And the amount of current needed to electrocute someone is quite small, about a thousandth of what the air conditioner would draw. So that load will not limit the shock current significantly at all. Thus the use of a separate grounding conductor. In that case equipment stops working but no shock hazard is created because of a bad neutral.

Much of the electrical code is written to have electricians build a system that will fail in a safe manner when a single problem develops.

A grounded "neutral" conductor is a current carrying conductor. An equipment grounding conductor (EGC for short) is not. That's one difference.

A Neutral carries Return Currents. A Ground should only carry Fault Current. Ground is supposed to be at your zero reference point in a system and you can't flow current through a conductor without dropping voltage across one.
Joe

Try to remember a neutral is a grounded conductor, an equipment ground is a grounding conductor. (think of the last letters in grounded- (not dead,) and the ng in grounding (near ground or earth) it may help.

Plee,

Welcome to ECN!

Your question is one which has been asked a few times before, so if more information is needed, try performing a "Search" for past threads, involving the topic of the term "Neutral".

Adding to the very helpful + concise information in the previous posts, here are a few details + a drawing to assist.

First off, as pointed out by others, the "Neutral" and the "Ground" wires have 2 totally different functions.

Beginning with the basics:
On _Grounded_ AC Systems, one of the System's Conductors will be physically connected to a "Ground" of some type.

If the AC System was on a Ship, the "Ground" would be the entire Ship's body. This is similar to the "Ground" definition of an Automobile's Electrical System - the "Ground" is the entire Frame & Body of the Car (except in this case, the Car's frame is used as a "Normal Circuit Conductor", whereas in the AC Power System, it would not be used this way).

For the common type of Grounded AC Systems - for Buildings built on the Earth, one Conductor of the AC Power System is physically "Bonded" to the Earth - via the "Grounding Electrode System", along with an additional Earth "Bond" at the Secondary terminals of a Utility Company's Transformer.

FYI: "BONDED" / "BONDING" is the physical connection of equipment and/or conductors to other equipment and/or conductors - as to make a permanent low Impedance connection

The typical System Conductor which gets "Ground Bonded" is the one which will offer the _LOWEST_ Voltage to Ground, depending on the type of System; and in many instances, it also is the conductor which is "Common" to the other circuit conductors - when applied as a "Multi Wire Branch Circuit".

Since we will keep things simple, the typical "Single Phase 3 Wire" type of Grounded AC Power System, will be used for working examples.

The Schematic below is a commonly used 1 Phase 3 Wire Transformer, for AC Power to Houses:



Notice the "Tapped Jumper" between Secondary Terminals "X2" and "X3". This is the Grounded "Neutral" Conductor.
It is Ground Bonded at the Transformer - as shown in this Schematic, and additionally it is Ground Bonded at each House's Main Service Panel - where the Service Entrance is, along with the kWh Meter and the Main Service Disconnect ("Main Breaker").

The "Neutral" is "Bonded" to both - the Metallic Enclosure of the Main Service Equipment, and to the House's Grounding Electrode System.

From there, the "Neutral" (referred to as "Grounded Conductor" here on out), remains "Isolated" from the "Bonded" metallic equipment used throughout the electrical system of the House.

The Metallic Equipment, along with the "3rd pin" of normal Receptacles (NEMA 5-15R, for example), is "Bonded" to the Grounded Conductor / Grounding Electrode System termination at the Main Service, so if any unintentional contact from an "Ungrounded System Conductor" occurs to the Metallic Enclosures or Raceways, there will be a path for current to flow back to the source - in this case, back to the Grounded Conductor of the System.
This results in (hopefully) tripping an Overcurrent Protection Device - such as a Circuit Breaker or Fuse.

If the AC System was not Bonded to the Enclosures in this fashion, an accidental contact between the Metallic Enclosures/Raceways and an Ungrounded Conductor (AKA "HOT WIRES"), would leave the metallic items "Live" - and would be a "Ground Fault For Personnel" type of shock hazard.

Poor Bonding terminations would also result in leaving a Ground Fault hazard, along with creating excessively heated connection points - ultimately leading to fire.

When "Auxiliary" Conductors are used with Circuits, which are used to physically Bond components / enclosures / raceways together, these are referred to as "Equipment Grounding Conductors".
They only carry current if there is an accidental fault situation, whereas the System's Grounded Conductor will carry current whenever it is used for circuitry.

The following examples of "Terminology" should be understood fully, in order to grasp the concepts of an AC System's "Neutral":

<OL TYPE=A>

[*] 2 Wire Circuit = 1 Ungrounded Conductor + 1 Grounded Conductor: Grounded Conductor is NOT a "Neutral", it carries the same current as the Ungrounded Conductor,


[*] 2 Wire Circuit = 2 Ungrounded Conductors - no Grounded Conductor: There is no Grounded Conductor involved with this circuit, both Ungrounded Conductors carry the same level of current,


[*] 3 Wire Multiwire Circuit from a 1 Phase 3 Wire Transformer = 2 Ungrounded Conductors + 1 Grounded Conductors: Loads are connected from each of the Ungrounded Conductors to the Grounded Conductor. This Grounded Conductor may be thought of as a "Neutral"
</OL>

*** In example "A", the Circuit used would be connected to a Load rated for 120 Volts.

If the Load draws 10 Amps from the Transformer, then 10 Amps would flow from the Transformer, to the load, and back to the Transformer, equally on both the Ungrounded Conductor and the Grounded Conductor.

This 2 Wire Circuit _DOES NOT_ have a "Neutral", since both Conductors carry the same current level, and the circuit is only a 2 wire circuit.

*** For example "B", this Circuit would be connected to a Load rated for 240 Volts.

If the Load draws 15 Amps, there will be 15 Amps flowing on the Conductors from the "Outer" Terminations of the Secondary - which are the Ungrounded Conductors.

This 15 Amps will flow between the Transformer and the Load, on the Ungrounded Conductors only.

The System's grounded Conductor - derived from the "Center Tap Point" of the Secondary windings, is not used for this Load's Circuit Connection.

*** Example "C" demonstrates a "3 Wire Multiwire Circuit".
Both Ungrounded Conductors, along with the Grounded Conductor are used in this type of Circuit.
The Ungrounded Conductors will be referred to as "L1" for "Line 1", and "L2" for "Line 2".
The Grounded Conductor will be referred to as "N" for "Neutral"
There is 120 Volts between "L1" and "N", 120 Volts between "L2" and "N", and 240 Volts between "L1" and "L2".

Let's say that the Load connected between "L1" and "N" draws 10 Amps, and the Load connected between "L2" and "N" draws 15 Amps.
The resulting Load Currents drawn from the Transformer on each Conductor will be:

* "L1" = 10 Amps,
* "N" = 5 Amps,
* "L2" = 15 Amps.

The System is said to be "Balanced" in this example, and the Grounded Conductor is functioning as a 'Neutral".

In all 3 examples described above (Circuits "A", "B" and "C"), each one will include an Equipment Grounding Conductor - which does not carry current during "Normal Operation", only if there's an accidental Ground Fault.

The Grounding of a system is done to reduce the stresses on the Insulation of the Conductors, along with "Stabilizing The Voltage To Ground".
This is kind of detailed, and way outside of the scope for this basic example discussion, but do keep in mind that "Ungrounded AC Power Systems" exist.

Along with Ungrounded systems, many various types of Grounded Systems exist.

There is a saying regarding AC Systems that goes:

"Not All Grounded Conductors Are 'Neutrals', and Not All 'Neutrals' Are Grounded".

Along these lines, if the Grounding on the Secondary of the Transformer, shown in the Schematic above, was done to the Conductor from Terminal "X1" instead of to the "Center Tapped Conductor", the System would still function properly - and all connected loads would work properly too.
The only thing that would change is the maximum Voltage to ground would now be 240 Volts, instead of 120 Volts.

Voltage to Ground from the Center Tapped Conductor will be 120 Volts.
Voltage to Ground from the "X4" Conductor would be 240 Volts.

Take a look at the Technical Reference section, for more details and drawings.

Hopefully this is of assistance to you.

Scott35

scott35

Thanks a lot for your insideful explaination. I think you not only a good practician, you also know the theory in great depth.
After reading your reply, I have the following question:
1. In your example A, it seems very much like a regular simple household 2 wire circuit, say, a circuit for a receptacle. If that is the case, your description would claim that the 'white' wire is NOT a 'Neutral', which seems to differ from most people would describe.
2. In the example C, you mentioned the Grounded conductor may be thought as a neutral.
I think in order to resolve my confusion for both examples, can you tell me what is the DEFINITION of 'Neutral', from both aspects of Physics ( I do have some Physics background) and Trade practice.

Your answer would be greatly appreciated!


Paul

I think I found my answer from an old posting by electric-ed:

(quote what electric-ed said)
The definition for neutral conductor that makes the most sense to me, and which happens to be the Canadian Electrical Code definition -
"Neutral means that conductor(when one exists) of a polyphase circuit, or a single phase, 3-wire circuit, which is intended to have a voltage such that the voltage differences between it and each of the other conductors are approximately equal in magnitude and equally spaced in phase."

According to this definition-

1. The grounded conductor of any wye connected system, or center tapped single-phase system, is a neutral.

2. The grounded conductor of a 2-wire, single phase system is not a neutral. (I just think of it as a "return".


3. The grounded conductor of a 4-wire delta is only a neutral for phases A and C, but not for the high leg.

4. The grounded conductor of a corner grounded 3-wire delta system is not a neutral.

Thanks

Hi Paul (great name ),

I think part of the problem lies with the strict definition of a neutral conductor versus the casual use of the term in everyday speech (it being shorter to say every time than "grounded conductor").

What if we have a 2-wire 120V branch circuit running from a normal 120/240V 3-wire service? The white wire on that branch circuit is not in itself a neutral by the strict definition, but it is connected to the neutral at the panel, and the current flowing on that branch circuit meets up with the neutral at that point.

In fact here in Britain the grounded conductor of a simple 2-wire circuit has been defined as a neutral by the I.E.E. for many years. Here's their definition from an old code book (although the first part referring to a 3-ph 4-w system is badly worded with its circular reference):

Is the grounded phase conductor of a corner-grounded delta considered to be a "neutral"? I'd think it would technically be a "grounded conductor", but would we call it a "neutral"?

[This message has been edited by SteveFehr (edited 07-27-2006).]

The corner delta is always going to be the one that makes you go Hmmm but you can't let it toss you. It is a grounded conductor that is not a neutral because it doesn't carry unbalanced current, it carries full circuit current.