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#6554 - 01/06/02 11:44 AM Neutral VS Ground  
Tom Post  Offline
Member
Joined: Sep 2001
Posts: 7
Philly
Ok, I'm looking for the best sparky explanation of the difference between a ground and a neutral. I mean, if the neutral wire and the ground wire both return to the main panel and are connected to the same bus bar or even a different bus bar yet are still connected to the same panel. What is the basic difference from attaching a ground wire to the neutral wire at an electrical receptacle instead of running a ground wire to a pipe. I know its the basics for you guys but I sure could use a good non tech explanation.
Thanks
Tom


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#6555 - 01/06/02 12:01 PM Re: Neutral VS Ground  
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
Do not connect the ground to the neutral at a receptacle. Doing so will cause a portion of the current to flow along your mechanical piping system. Imagine connecting the neutral & ground together at a garbage disposal. Now the current path back to your panel will divide between your neutral conductor and drainage&piping system. If a plumber were to open up a portion of your piping, he would be in series with that current and it will flow through him. He may also be wet. He might die. Even if no one services your piping, the current flowing will likely encounter a high resistance path at certain piping joints which will generate heat, or if there is a loose connection this may arc and cause a fire. Under certain conditions, someone touching an appliance may get a shock. Also, if your main neutral opens up, your piping may carry enough current to melt solder joints and cause major flooding.


#6556 - 01/06/02 12:14 PM Re: Neutral VS Ground  
Elzappr  Offline
Member
Joined: Dec 2001
Posts: 270
Oregon
Its just a matter of safety. The neutral conductor carries the normal "return" current, or "unbalanced" current, depending on the context. The grounding conductor is only there to conduct current during an accidental "hot-to-ground" contact. That is, if a wire gets pinched or damaged or comes loose and touches the metal enclosure, and that metal enclosure is bonded with a grounding conductor, the resulting ground fault current will be assuredly conducted back to the neutral at the service, and complete the fault current loop necessary to trip breakers or blow fuses. You don't want to connect the neutral and ground together anyplace downstream from the service because then you would be paralleling the neutral current. Paralleling the neutral would cause current to flow throughout the metal of the building, the plumbing, as well as the grounding conductor, creating galvanic corrosion and life safety concerns in the event that the actual neutral conductor comes loose and all the return current is flowing through the metal enclosure, plumbing pipes, building steel, and grounding conductor. If someone were to be holding on to two pieces of a newly opened section of pipe, they could be killed if that pipe were relied upon to carry the brunt of the neutral curent. The same would apply to any grounding conductor, or section of building steel, of section of conduit enclosing conductors.


#6557 - 01/06/02 01:39 PM Re: Neutral VS Ground  
George Corron  Offline
Member
Joined: May 2001
Posts: 717
Lorton, Va USA
Redsy,
Garbage disposal is a good example, but I actually had to troubleshoot and fix a homeowners self induced problem in an old house. He had added an "instant" hot for his bathroom upstairs in an older house along with a subpanel, he neglected to separate his neutrals and grounds. Now he had overcurrent on his shower controls, got zapped everytime he was wet, kinda served him right, buuuuut, boy was that dangerous (cast iron DWV was a pretty good conductor). That was always the best 'splanation I could give for that one. [Linked Image]


#6558 - 01/06/02 03:21 PM Re: Neutral VS Ground  
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,306
Noodles, i.e. Grounded conductors carry current, Grounding conductors do not........ [Linked Image]
when i get confused, K.I.S.S. is my motto

[This message has been edited by sparky (edited 01-06-2002).]


#6559 - 01/06/02 03:31 PM Re: Neutral VS Ground  
watthead  Offline
Member
Joined: Oct 2001
Posts: 172
South Carolina
Tom
Far too many even so-called electricians can hook up power to something without the protection proper grounding provides. Yours is an excellent question, and you should be very comfortable with the answers you receive before you proceed with any electrical hook-ups. There are several good books on grounding that are written for the beginner and are easy to comprehend. The grounding of the system or circuit is simply put, the most important part of the connections that are made. These books will explain better than me the difference between: service ground, equipment grounding conductors, grounded conductors, neutral conductors, bonding, main bonding jumper, equipment bonding jumper, etc. along with proper sizing techniques. One common misconception is that the white conductor of a 12/2WG (common house wire ) is a neutral. If you have 12/2WG connected to a receptacle there is not a neutral involved this white wire is a grounded conductor. You would only have a neutral if you were using 12/3WG and connected two ungrounded conductors to different 120v legs which would produce 240v between them, and you used some 120v power to create a neutral which carries the unbalanced current. If you connected two 100 watt light bulbs to one 120v line and the neutral, and one 100 watt bulb to the other 120v line and neutral, the neutral would only carry 100 watts of current ( or the unbalanced current ) between the two 120v lines. If your white ( grounded conductor ) to the receptacle is broken and the black ( ungrounded conductor ) contacts the metal case of the equipment it is then that the ground ( equipment grounding conductor ) would trip the breaker ( overcurrent protection device ). The sad fact that is unknown to many installers is the grounding system does not operate until there is a problem such as a short or fault that requires its protection, and much too often this safety system has been improperly wired or is nonexistent. A common example of improper wiring is the grounded conductor and the equipment grounding conductor being connected under the same screw on the neutral buss. If this one connection is compromised, you loose both paths for fault current to return to the overcurrent protection device,without which the breaker will not trip. I hope this helps you as your question is not simple to answer even by a simpleton like me.


#6560 - 01/07/02 10:55 AM Re: Neutral VS Ground  
Tom Post  Offline
Member
Joined: Sep 2001
Posts: 7
Philly
Thanks Elzappr and Watthead. I appreciate the not to technical yet strait on info.
As I understand you, the ground serves no function UNTIL a fault occurs. That is why they are found on the same bus bar. They are only in place to complete the fault circuit.
Any other explanations would be welcomed.
Again THANKS.
Tom


#6561 - 01/07/02 04:52 PM Re: Neutral VS Ground  
rbiro  Offline
Member
Joined: Oct 2001
Posts: 19
Pacifica, CA USA
Again, not quite on topic but I believe it is useful.

One thing to remember is that the neutral and ground are bonded, so objectionable current does flow over the grounding system.

If you stand in a mud puddle and grab a ground wire, you will get shocked. You just may not be able to feel it. (Don't try this because you may feel it, and it may kill you.)

The idea behind large sections of the code is to make sure the amount of current flowing on the ground is so small as to be negligble and preferably even not measureable.

One mental exercise I found to be very useful was to imagine standing in a mud puddle holding an old electric drill with a grounded metal case and estimating what would happen if a msssive ground fault occurred at different places in the electrical system, including places like on the cable tv and a sattelite dish.

Currently in my home, the ground bus in one of the sub panels is bonded directly to the water pipes for historical reasons. Based on the above exercies, I think that may be a bad thing.



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