Neutral and Ground

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  #1  
Old 09-26-05, 09:54 AM
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Neutral and Ground

I'm trying to learn.

In the main panel the ground and neurtral are connected on the same bus bar, correct?

Once you go into the subpanel the ground is attached to the gound bar and the neutral is attached to an isolated neutral bar, correct?

Since the two are attached in the main panel, dont they remain connected in the subpanel by virtue of the main panel connection? I hope this makes since.

If you were to use a continuity tester (if there is such a thing) wouldn't the ground and the neutral in the subpanel show that they were still connected?
 
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  #2  
Old 09-26-05, 10:17 AM
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Originally Posted by gmasingale
In the main panel the ground and neurtral are connected on the same bus bar, correct?
Correct.

Once you go into the subpanel the ground is attached to the gound bar and the neutral is attached to an isolated neutral bar, correct?
Correct.

Since the two are attached in the main panel, dont they remain connected in the subpanel by virtue of the main panel connection?
Yes, they are electrically connected throughout the home wiring.

The neutral (grounded conductor) and ground (grounding conductor) must be bonded together in one and only one spot. That spot is in the main panel. Consider the ground wire to be an emergency backup for the neutral. If the neutral wire becomes broken, then the grounding system serves as a backup for diverting the electricity back to the source transformer and hopefully tripping the breaker.

This gets a little complicated. If the ground and neutral wires were bonded outside of the main panel box, then current would be flowing in both the neutral and ground. This becomes a problem because the ground is also connected to your plumbing and appliance frames. Current flowing through metal where human contact can occur presents an electrocution hazard. Therefore, the ground and neutral can be bonded only in the main panel box.
 
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Old 09-26-05, 10:29 AM
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Thanks for the info.
 
  #4  
Old 09-26-05, 10:30 AM
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The answers to your questions are all yes, with a caveat or two.

In a home residential system, the ground and neutral are connected at one place. This is usually done at the main panel. Sometimes it is done at the meter itself, but that is less common these days.

Yes, a continuity tester will show that the ground and neutral are connected. It will show this at the main panel (where they are connected), it will show this at a sub panel, and it will show this at a receptacle or other electrical device on a properly wired grounded circuit. Note that if you actually measure the resistance between the two, you would measure more resistance between the two at a sub panel or a receptacle than you would at the main panel. The actual resistance is a function of the distance and the wire size.

They are connected together for safety. The ground provides an alternate path for current to flow in the event of a wiring problem. For example, if a hot wires comes loose in a washing machine and accidentally touches the metal shell of the washer, it will immediately be routed through the ground wire back to the main panel, where it return to the power company. The amount of current will trip the breaker and the circuit will be off.

The reason they are not connected together at a sub panel and/or at a receptacle (or other electrical appliance) is because the neutral wire carries current, and current on a ground wire is not a good thing.
 
  #5  
Old 09-26-05, 11:14 AM
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Should more than one grounding rod ever be used.

What if the main panel is separated from the subpanel by 100 feet.

What if it is in the same dwelling. The main panel is mounted on the exterior of the main structure and the subpanel is mounted on the exterior of the same structure but separated by 100 feet.
 
  #6  
Old 09-26-05, 11:32 AM
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The more grounding rods the better, but they should all be interconnected via a wire. So essentially they are all acting as a single system.

It doesn't matter how far apart the panels are. Special rules, however, do apply if the panels are in separate structures vs. one structure. Within one structure, grounding wires and neutral wires can be connected in one and only one place. In an outbuilding, they may not be connected at all in the outbuilding itself (depending on other factors).

One important thing to remember is that you have two grounding systems, they serve separate purposes, and do not depend on each other. Grounding rods are part of the Grounding Electrode System (GES) and are there primarily to protect against outside events such as downed power lines and electrical storms. Equipment Grounding Conductors (EGC) which run from the panel to your outlets are there primarily to protect people and the building from faults inside the house. Never get these two systems mixed up, or mistake one form of protection for another.
 
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