Ground/neutral

alanc5

Member
Join Date
Apr 2002
Location
Charleston, SC
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I HAVE SOME FELLOW EMPLOYEE'S WHO INSIST THAT A NEUTRAL AND A GROUND ARE THE SAME THING. I DISAGREE, I KNOW THAT A GROUND IS USED TO IDENTIFY A ZERO POTENTIAL AND EVERY THING ELSE IS REFERED TO AS POSITIVE OR NEGATIVE. WHAT I DON'T LIKE IS THAT IN THE PLANT I WORK IN NEUTRALS(WHITE) AND GROUNDS(GREEN) ARE LANDED ON THE SAME BUSES.
I GET A LITTLE NERVOUS JUST LOOKING AT SOME BUSES. I WAS TOUGHT THAT A GROUND ALSO SERVES AS SHORT PROTECTION AND A NEUTRAL SERVED AS A RETURN FROM THE LOAD SIDE( OR RETURN FROM THE HOT)....AM I TOTALY OUT OF MY MIND???? ARE POINTS OF VIEW ARE WELCOME...
 
You are correct and your fellow employee's are wrong.

With this said, we need to go on and say often neutrals are tied to ground, but not always.

In day-in day-out world, I think that is the really important point...not all white "neutrals" are necessarily grounded and, therefore, may not necessarily be at the same potential as a green "gound" wire.

It is a normal practice to tie grounds and neutrals to the same bus bar and not one that should cause you concern.

I suspect others in this forum will be willing to give more technical whys and where-fors, but in short, don't start thinking of grounds and neutrals as the same...that's the kind of stuff that gets people killed!

Steve
 
A ground is absolutly not a nuetral!!

Your "ideas" are somewhat correct. A ground is just that, a ground.
A neutral (in the context you use) according to the NEC, is a grounded conductor, and a neutral.
A ground (in the context you use) according to the NEC, is the grounding conductor.


A grounding conductor is always a NON-CURRENT CARRYING conductor.(except in case of ground fault)
A grounded conductor is a grounded CURRENT CARRYING conductor.
A neutral conductor (whether grounded or not) carries the UNBALANCED current of the ungrounded conductors (hot wires)
Neutrals can be grounded conductors, and grounded conductors can be neutrals.
A neutral is not necessarily a grounded conductor.
A grounded conductor is not necessarily a neutral.


Grounding conductors and neutrals all tying into the same "buss bar" is common, that is how the neutral gets grounded. There should also be a large grounding conductor going to a copper rod in the ground or one of the other methods of grounding at these locations as well.

Your comment about positive and negative reference from ground are not correct. AC current is constantly alternating polarity, so there is no such thing as negative potential.
 
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Ignore those "fellow employees", though you don't have to be nervous about those panels with the grounds and neutrals connected to the same bus... Unless they are subpanels!

Someone here will give an excellent explanation of this, but in the meantime...

At ONE point (the main panel), the neutral is connected to ground... This is where the neutral originates from. The neutral is supposed to have current flowing on it, but the ground should have NONE!

The neutral is also called the grounded conductor (emphasis on the "ed"), because it IS connected to ground (at the main panel).

Notice how you connect a control transformer to provide 120VAC. You ground one of the secondary leads, and this becomes the origin for a neutral (hence the name "grounded") conductor. IOW, you're creating a new power source.

beerchug

-Eric
 
Eric Nelson said:


Notice how you connect a control transformer to provide 120VAC. You ground one of the secondary leads, and this becomes the origin for a neutral (hence the name "grounded") conductor. IOW, you're creating a new power source.

beerchug

-Eric
Provided we are talking single phase
Keep in mind that if the secondary of the transformer only has 2 leads then you have no neutral. If it has 3 leads then you have two "hots" and a "neutral". (most likely) Hot to Hot 240v and Hot to Neutral 120v. If the Neutral is not grounded then who knows what you will get (voltage) from ground to any 1 of the three. If it is grounded then the voltage will be the same from hot to neutral or ground.
 
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93lt1 said:

Provided we are talking single phase
Keep in mind that if the secondary of the transformer only has 2 leads then you have no neutral.

Until you ground one of those leads, creating a "grounded" conductor, AKA neutral.

Before you junp on that statement... :D

I did read your:

"Neutrals can be grounded conductors, and grounded conductors can be neutrals.
A neutral is not necessarily a grounded conductor.
A grounded conductor is not necessarily a neutral."

and I agree, but this might just make an explanation more confusing for alanc5. For simplicity, assume that they are one in the same. And sticking to single phase is a good starting point as you can use house wiring (in the US at least) as an example.

Once we have ironed out the simplified version, we can get into more "advanced" stuff... ;)

-Eric
 
The grounded (or neutral) conductor carries the unbalanced load, so therefore it can be a current carrying conductor. 110V is unbalanced. 220V is balanced.
Ex. Your hotwater heater or well pump may be 220V and requires no "neutral" but your alarm clock is 110V and it requires a neutral.

The grounding (or ground) conductor is for a fault condition. And can be sized considerablly smaller that the other conductors.

The connection between the grounded and the grounding conductor shall be done at the main service entrance (main power disconnect). If your building has more than one service than it is done at each service. It is a code requirement at every main service entrance - including your house.

In subpanels fed from the main service entrance they are not supposed to be connected together. The grounding and the grounded conductors are to be kept seperate here. This is so if a fault condition arizes the grounded conductor carries the voltage directly to ground and not to the "neutral" possibly injuring someone.

From what I am reading in your post it sounds like you may have a transformer (fed from a 3 phase system) feeding the buss for your single phase power. So in a sense the buss becomes a "main service entrance" from the transformer.
 
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My suggestion alanc5 is look closer at NEC code (specifically 250-xx) and if you can buy the Americans Electricians Handbook


Comment: Code references are based on both the 1996 and 1999 National Electrical Code.


VOLTAGE BETWEEN METAL PARTS TO EARTH

Proper Neutral-to-Ground Connection

When a neutral-to-ground connection is properly made in accordance with the NEC, the voltage between any metal part of the electrical system to the earth will be zero volts.


Improper Neutral-to-Ground Connection

The National Electrical Code requires a neutral-to-ground connection to be made at service equipment only and there shall not be any neutral-to-ground connection on the load side of service equipment [250-23(a), 250-24(a)(5)], except as permitted in Section 250-61 [250-142].


Comment: Because of confusion on proper grounding and bonding, many electricians install the main bonding jumper that is supplied with the panelboard on the load side of service equipment making an improper neutral-to-ground connection (I personally did it many times).


Electromagnetic Interference

When a neutral-to-ground connection is made at the load side of service equipment in violation of the NEC, the feeder neutral current will divide and return on both the feeder’s metal raceway as well as the feeder’s neutral conductor (parallel path). This improper neutral-to-ground connection permits neutral current to return on the metal parts of electrical equipment (i.e. metal raceways).


When neutral current (or any ac current) travels on the metal parts of electrical equipment, the electromagnetic field generated from the flow of alternating current is not able to be canceled. This uncanceled electromagnetic field can negatively impact sensitive electronic devices.


IMPORTANT: Improper neutral-to-ground connections create parallel paths for neutral currents on the metal parts of the electrical system, including any metal shielding of low-voltage and limited-energy cables!


Comment: There is the unproven health issue about the effects of electromagnetic fields on humans.


Elevated Ground Voltage

When a neutral-to-ground connection is made at the load side of service equipment in violation of the NEC, the voltage difference between the equipment ground and the earth will rise to equal the voltage drop of the neutral conductor at that location in the electrical system. The elevated ground voltage can be calculated by the following formula:

E(Voltage Drop) = I(Current) x R(Resistance)


Comment: Today’s office buildings contain large quantities of single-phase nonlinear loads such as personal computers and laser printers. These loads, when on a Wye 4-wire 3-phase system, produce odd triplen harmonic currents that add (instead of cancel) on the neutral conductor causing the neutral conductor to carry elevated neutral current. In addition, when high amperage loads such as laser printers or copiers cycle on, they cause rapid increases of neutral current which elevates the voltage on the grounding conductor.

Feeder. If a neutral-to-ground connection were made at the panelboard in violation of the NEC, the feeder neutral current would divide and return on both the feeder metal raceway and the feeder neutral conductor. Under these conditions, the voltage difference between any part of the electrical system to the earth will have risen to 1.25 volts (the voltage drop of the feeder neutral).

Comment: The voltage drop of the feeder neutral conductor was 3 volts in Figure 1-1, but the parallel paths for the neutral current reduces the feeder voltage drop to 1.25 volts (for the purpose of example) in Figure 1-3.

Branch Circuit. If a neutral-to-ground connection were made at the receptacle in violation of the NEC, the branch circuit neutral current would divide and return on both the branch circuit metal raceway and the branch circuit neutral conductor. Under this condition, the voltage difference between any part of the electrical system to the earth would have risen to some value more than 3 volts but less than 4.5 volts.


VOLTAGE BETWEEN NEUTRAL AND GROUND

Proper Installation.

In a proper neutral-to-ground installation, the voltage between the neutral conductor and any metal part of the electrical system will be equal to the voltage drop of the neutral conductor in accordance with the following:


At service equipment, the voltage difference between the neutral conductor and the service equipment case will be 0 volts.


At panelboards, the voltage difference between the neutral conductor and the equipment grounding conductor (panelboard case) will be equal to the voltage drop of the feeder neutral conductor, which is 3 volts.


At branch circuits, the voltage difference between the neutral conductor and the equipment ground (ground contacts of the receptacle) will be equal to the voltage drop of the feeder and branch circuit neutral conductors, which is 4.5 volts (3 volts feeder and 1.5 volts branch circuit).


Comment: Computer and copier manufacturers insist (for warrantee purposes), that the voltage between the neutral and the ground contacts of the receptacle should not exceed 1 to 3 volts, and some manufacturers actually specify that the voltage must not exceed .5 volt! This is practically impossible to achieve in the real world without violating the NEC and I wonder if these manufacturers have any clue as to why they contain this requirement in their specifications. Maybe this subject should be explored in depth in the future.


Improper Installation

Feeder. If a neutral-to-ground connection were made at the panelboard in violation of the NEC, the voltage difference between the panelboard case ground to the neutral conductor would be 0 volts. Under this condition, the voltage difference at the receptacle contacts would only be equal to the voltage drop of the branch circuit conductors.


Branch Circuit. If a neutral-to-ground connection were made at the receptacle in violation of the NEC, the voltage difference between the grounding contacts of the receptacle to the neutral conductor would be 0 volts.

Comment: At service equipment, the voltage between the neutral-to-ground will always 0 volts.
 
One other consideration is a control transformer in a panel tapped from two of the threee conductors in a three phase power source and intended to provide 120 VAC. If you don't ground the neutral side, the voltage between the two wires on the secondary side will be 120 VAC, but the voltage from either wire to ground will not be zero unless you tie one side to ground. Then you have one wire that is now neutral, and the other is your line, or power, wire.

In a 120 VAC single phase line the current through line and neutral varies from max to zero at 60 Hz, but the current direction is always the same in both lines. Current doesn't flow backwards in the neutral of a properly grounded system.
 
Which is how a GFCI (Ground Fault Circuit Interrupter) magically detects ground faults...

When the current on the hot and neutral leads varies by more than a specified amount, the current is going somewhere... More than likely it's going to ground (but NOT via the neutral wire).

This path to ground may include a living creature that is not designed to carry that much current... :eek:

-Eric

P.S. Nice work Ron!
 
Tom Jenkins said:
One other consideration is a control transformer in a panel tapped from two of the threee conductors in a three phase power source and intended to provide 120 VAC.

It really doesnt matter where the power on the primary is coming from.

If you don't ground the neutral side, the voltage between the two wires on the secondary side will be 120 VAC, but the voltage from either wire to ground will not be zero unless you tie one side to ground. Then you have one wire that is now neutral, and the other is your line, or power, wire.

Not neutral, but grounded conductor. If the transformer was intended to provide 240/120,and the end of the two secondary coils were grounded and tied together then it would be a neutral.
 

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