Grounds vs. Neutrals

[etbrown4]

Kindly don't beat me up, as I'm somewhat new to this forum!


We all know the NEC definitely treats grounds as separate and distinct from neutrals.


For purposes of this question, let's assume that the neutral and ground bar is bonded to the service panel.


I've long wondered that since they are both often attached to the same grounding or neutral bar in the panel, if there is truly a difference - practically speaking. (We know the NEC requires wire colors to be different.)


So here is the question: If the ground wire is fully insulated over it's full length, and say, it's run 20 or 100 feet from the service to a junction box. Once in that junction box, is there any practical difference ...electrically speaking, and from the point of view of safety... as to whether that wire could safely serve as a neutral or as a ground? (I know this was covered in our first electrical class, but I've still wondered about it)

 

[iwire]

The practical difference is that if you used a equipment grounding conductor as a circuit conductor and that conductor becomes disconnected or broken it can cause grounded parts to become live.

 

[xformer]

So here is the question: If the ground wire is fully insulated over it's full length, and say, it's run 20 or 100 feet from the service to a junction box. Once in that junction box, is there any practical difference ...electrically speaking, and from the point of view of safety... as to whether that wire could safely serve as a neutral or as a ground? (I know this was covered in our first electrical class, but I've still wondered about it)

Hello and welcome to the forum.

IMHO, with the scenerio you have described, and just focusing on the conductors themselves, electrically speaking, the ground wire could serve as a neutral as long as GFCI protection is not afforded to the circuit. (this by the way is an electrical no-no.) Code requires us to run a seperate conductor "the grounding conductor" for safety reasons. What most people believe is that electricity flows from Hot to Ground. Electricity DOES NOT not flow from Hot to Ground...... It flows from Hot back to source through any and all available means... Constructing a low impedance path, ie: the grounding conductor, back to the source provides that safety you and me.

 

[winnie]

Because the EGC and the neutral conductors are attached together, they will be at approximately the same _voltage_.

The key difference between them is _current_. The neutral conductor is supposed to carry circuit current in normal operation. For a 'two wire' circuit, the neutral carries the same current as the 'hot'. The EGC is only supposed to carry current during faults.

Because the neutral is supposed to be at ground potential, then you could conceive of using the neutral for bonding of things like chassis. As Iwire notes, this works just fine until the neutral gets interrupted!

-Jon

 

[xformer]

Because the EGC and the neutral conductors are attached together, they will be at approximately the same _voltage_.

The key difference between them is _current_. The neutral conductor is supposed to carry circuit current in normal operation. For a 'two wire' circuit, the neutral carries the same current as the 'hot'. The EGC is only supposed to carry current during faults.

Because the neutral is supposed to be at ground potential, then you could conceive of using the neutral for bonding of things like chassis. As Iwire notes, this works just fine until the neutral gets interrupted!

-Jon

I concur with Iwire and Winne

 

[kwired]

They are the same thing - at the service equipment. Beyond the service equipment they are only the same thing when there is no load.

In addition to some of what has already been mentioned...

Once you put load on the neutral conductor you begin to increase voltage drop on that conductor, so at the load end of the circuit there will be some potential difference between the two conductors. How much difference will depend on the actual load and actual conductor resistance.

Using the "grounded" (neutral) conductor for equipment grounding will raise the voltage of the frame of equipment that is connected to the improperly done equipment grounding conductor to a level equal to the voltage drop on that conductor to other grounded objects and increase the shock potential when touching those objects and the mentioned equipment at the same time. Often times this voltage drop is small and nothing significant ever happens, but when conditions are right we get sudden unexpected results, and many times an electrocution ends up being the result. GFCI doesn't protect you from this either, in most "bootleg" ground incidents, as the voltage drop has already happened before the connection to the GFCI receptacle, they will trip if there is current going to ground on the load side of the GFCI though, but may happen immediately after making the bootleg connection - just depends on conditions of the install.

 

[fmtjfw]

Safety

Safety

Here is a reason the neutral and the grounding conductor are separate.

Assume you have the neutral and the grounding conductors connected together at the main circuit breaker cabinet. Assume the voltage is 0 volts where they are connected. Assume the hot voltage is 120 volts. Further assume the wiring is NM (Romex?) and that the circuit terminates in a metal box with a receptacle.

Now short circuit the receptacle. Since the neutral and the hot conductor are the same size and length, they have the same resistance and will divide the 120 volts evenly until the breaker trips. So the neutral will be at 60 volts, the hot will be at 60 volts in the box, but the grounding will still be at 0 volts (since no current is flowing in it).

So with a separate neutral/grounding the box and metal parts of the thing plugged into it stay at 0 volts. Had the neutral also be used as the grounding, the voltage of the box would have been an unsafe 60 volts.

[Yes, this doesn't apply to ground faults]

 

[kwired]

Here is a reason the neutral and the grounding conductor are separate.

Assume you have the neutral and the grounding conductors connected together at the main circuit breaker cabinet. Assume the voltage is 0 volts where they are connected. Assume the hot voltage is 120 volts. Further assume the wiring is NM (Romex?) and that the circuit terminates in a metal box with a receptacle.

Now short circuit the receptacle. Since the neutral and the hot conductor are the same size and length, they have the same resistance and will divide the 120 volts evenly until the breaker trips. So the neutral will be at 60 volts, the hot will be at 60 volts in the box, but the grounding will still be at 0 volts (since no current is flowing in it).

So with a separate neutral/grounding the box and metal parts of the thing plugged into it stay at 0 volts. Had the neutral also be used as the grounding, the voltage of the box would have been an unsafe 60 volts.

[Yes, this doesn't apply to ground faults]

Do you know which happens more, ungrounded to grounded or ungrounded to neutral faults?

I am guessing faults to ground are likely more common.

Though there is some merit to your explanation I am going to shoot down the idea that this is by any means the only reason we are supposed to keep grounded/grounding conductors separate. The reason you bring up also is one that will usually be very short in duration when it does happen. Other mentioned conditions can go on indefinitely.

 

[fmtjfw]

Do you know which happens more, ungrounded to grounded or ungrounded to neutral faults?

I am guessing faults to ground are likely more common.

Though there is some merit to your explanation I am going to shoot down the idea that this is by any means the only reason we are supposed to keep grounded/grounding conductors separate. The reason you bring up also is one that will usually be very short in duration when it does happen. Other mentioned conditions can go on indefinitely.

"Here is a reason the neutral and the grounding conductor are separate."

I could have added parallel grounding paths.
I could have discussed the elevated voltage inherent in using any neutral as a grounding conductor.
I could have added that having a separate grounding conductor helps prevent elevated voltages if the neutral is disconnected and the hot ground faults at the same time.

I chose to take a simple example and provide a simple explanation.
I have no idea as to the level of this newcomer to the forum.

The basic idea is to have the grounding conductor not carry any current, except under ground fault (to it) conditions so that the grounded objects stay at a low voltage to "ground".

Consider Zinsco and Stablok

 

[kwired]

"Here is a reason the neutral and the grounding conductor are separate."

I could have added parallel grounding paths.
I could have discussed the elevated voltage inherent in using any neutral as a grounding conductor.
I could have added that having a separate grounding conductor helps prevent elevated voltages if the neutral is disconnected and the hot ground faults at the same time.

I chose to take a simple example and provide a simple explanation.
I have no idea as to the level of this newcomer to the forum.

The basic idea is to have the grounding conductor not carry any current, except under ground fault (to it) conditions so that the grounded objects stay at a low voltage to "ground".

Consider Zinsco and Stablok

My apologies.... somehow I saw "the" reason.

But it still was good info to add to the discussion from both of us

 

[fmtjfw]

Yea, I often respond to what I read, not what is written.

It is hard to guess at what level the answer(s) should be. As a teacher I often try to simplify things, at least as a first step. That way if fine fewer EGO problems (Eyes Glazed Over).

I can recall a long discussion about PVC expansion joints. I finally came up with a step-by-step process to calculate it and another guy came up with a slick spreadsheet that seemed to be well received. Back and forth is a fine way to have a civilized discussion.

 

[mbrooke]

Inductive heating in conduit is another problem.

 

[Little Bill]

Do you know which happens more, ungrounded to grounded or ungrounded to neutral faults?

I am guessing faults to ground are likely more common.

Did you read what you wrote?

Ungrounded to grounded = hot to neutral
ungrounded to neutral = same thing

No, I'm not talking about the true definition of "neutral" but what is commonly known as the neutral, ie; grounded conductor.

 

[kwired]

Did you read what you wrote?

Ungrounded to grounded = hot to neutral
ungrounded to neutral = same thing

No, I'm not talking about the true definition of "neutral" but what is commonly known as the neutral, ie; grounded conductor.

Well that is what I get for trying to use proper terminology, which I try to do most of the time just to be consistent with NEC, especially when contributing things to this site. I ended up confusing myself some and didn't read back what I wrote to make sure it said what I meant:ashamed1:

I was trying to say "hot" to "ground" vs "hot" to "neutral"

 

[Little Bill]

Well that is what I get for trying to use proper terminology, which I try to do most of the time just to be consistent with NEC, especially when contributing things to this site. I ended up confusing myself some and didn't read back what I wrote to make sure it said what I meant:ashamed1:

I was trying to say "hot" to "ground" vs "hot" to "neutral"

It's time to stop the PC. On with the "hot" & "neutral"!

 

[FionaZuppa]

past the service panel the ground and neutral may be isolated, and in most cases they are. example, the neutral on std outlet is not attached to the ground in any way, thus the current flows through white/black only. if for some reason the neutral becomes disconnected then the outlet cant flow current. if the ground however happens to touch neutral then the current is being carried across all 3 wires (50/50 on ground-neutral), and if neutral lifts off and ground touches where neutral was, current can still flow. some of these scenarios are protected by GFI (current only on hot-neutral), etc.

so i guess it matters how things are wired and what scenario is at play.