Sub Panel Neutral Wire Question

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  #1  
Old 07-01-04, 05:19 AM
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Sub Panel Neutral Wire Question

What is the purpose of not bonding the neutral bus bar to the panel housing on a sub panel? And does the same apply for a ground? I intended to run another ground bar in the same proximity as the sub panel and ground the panel through the wire feed and the local ground bar.

Thanks

Leslie
 
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  #2  
Old 07-01-04, 05:28 AM
mgb
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The reason for not bonding the neutral bar to the subpanel is to not allow any current from the neutral to travel back to the main panel via the equipment ground. The seperate ground bar that you mount in the subpanel is bonded to the subpanel by way of the screws that attach it. All your ground wires attach to it and the neutral wires go to the neutral bar. When you said you intend to run another ground bar did you mean ground rod?
 
  #3  
Old 07-01-04, 07:50 AM
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Sub panel

Sorry, I meant rod. So, let me get this straight. The neutral conductor runs from the common bus in the main panel to a isolated neutral only bus in the sub panel and I should drop a ground rod next to the sub panel to create a ground path isolated from the main panel but bonded to the subpanel? I want to make sure its both safe and to code before I start laying wire.

Thanks

Leslie
 
  #4  
Old 07-01-04, 07:57 AM
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Dude, you are way off. And quite honestly, you are scaring me.

Yes, you have to run a neutral AND a ground wire from the main panel to the sub panel. The neutral Bus will NOT be connected to the metal casing of the subpanel. The Ground Bus will be connected to the panel.

The reason for NOT connecting (bonding) the neutral bus to the panel is because the Ground bus IS bonded to the panel. That would allow current to enter the Ground Bus from the Neutral Bus and travel back to the main panel over the ground wires. You never want current on your ground wires during normal conditions.

You don't want different ground rods all around your house. Everywhere you drive a ground rod there is a different potiential (Voltage). Although we like to pretend it is, the Earth is not the same potential (Voltage) everywhere at one time. If the Ground Rods aren't bonded together to the other ground rods it could be dangerous if the difference in those potentials is very large. If you happen to touch the two different grounding areas at the same time, it could hurt... lots
 

Last edited by kuhurdler; 07-01-04 at 08:10 AM.
  #5  
Old 07-01-04, 08:05 AM
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Sub Panel

Originally Posted by kuhurdler
Dude, you are way off. And quite honestly, you are scaring me.

Yes, you have to run a neutral AND a ground wire from the main panel to the sub panel. The neutral Bus will NOT be connected to the metal casing of the subpanel. The Ground Bus will be connected to the panel.
Sorry, my mind is trying to do way to many things at one time right now. But I now fully understand what everyone is trying to explain. Just needed to put it on paper. It makes complete sense know that I think about it. Is there a certain type of screw needed for the neutral bar installation? I believe I read somewhere that sheet metal screws violated code but I am not sure.

Thanks

Leslie
 
  #6  
Old 07-01-04, 08:09 AM
mgb
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Yes you must run a neutral wire back to the main panel, otherwise nothing would work as it wouldn't be a complete circuit. Code wise you might be able to get by without running a ground wire back to the main if you drive a ground rod near the sub panel but the neutral wire coming from the main panel has to be insulated. I'm not positive about this method but maybe somone else will chime in to let us know. Personally I would run a ground wire back to the main panel and drive the ground rod too.
 
  #7  
Old 07-01-04, 08:30 AM
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If the new sub-panel is located on a seperate structure, such as a detached garage, a Grounding Electrode is required at the S-P location. A additional G-E is not required if the S-P is located in the same structure as the Service panel.

The Wiring Method between the Service panel and the new S-P will be either a cable or a raceway, such as PVC conduit. The cable must have a bare Equiptment Grounding Condutor. If you install a raceway,include an Green EGC along with the 3 Feeder conductors.The use of either Wiring Method will result in 4 conductors between the Service panel and the new S-P.

Ther new S-P should be equipped with a Neutral terminal bar which is isolated from Ground, and it must remain isolated. You will have to add to the new S-P a seperate Grounding terminal bar which is throughly Bonded to the exposed ( no paint!) metallic surface of the S-P enclosure. The Feeder EGC and the Branch-Circuit EGC's will terminate on the seperate Grounding terminal bar.

Good Luck & Enjoy the Experience!!!!!!!!!11
 
  #8  
Old 07-01-04, 09:00 AM
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Sub Panel

Originally Posted by PATTBAA
If the new sub-panel is located on a seperate structure, such as a detached garage, a Grounding Electrode is required at the S-P location. A additional G-E is not required if the S-P is located in the same structure as the Service panel.

The Wiring Method between the Service panel and the new S-P will be either a cable or a raceway, such as PVC conduit. The cable must have a bare Equiptment Grounding Condutor. If you install a raceway,include an Green EGC along with the 3 Feeder conductors.The use of either Wiring Method will result in 4 conductors between the Service panel and the new S-P.

Ther new S-P should be equipped with a Neutral terminal bar which is isolated from Ground, and it must remain isolated. You will have to add to the new S-P a seperate Grounding terminal bar which is throughly Bonded to the exposed ( no paint!) metallic surface of the S-P enclosure. The Feeder EGC and the Branch-Circuit EGC's will terminate on the seperate Grounding terminal bar.

Good Luck & Enjoy the Experience!!!!!!!!!11

Thanks for the information. It is amazing how just a little expert information can make everything seem so simple.

Leslie
 
  #9  
Old 07-01-04, 09:08 AM
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Sub Panel

For this application does the grounding conductor from the main S-P to the Sub S-P have to be the same gauge as the rest? That is does it need to be a #2 or can I reduce it to a #6 copper wire.

Leslie
 
  #10  
Old 07-01-04, 10:12 AM
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No the grounding wire between panels need not be as heavy as the other wires. #6 is fine. What is the size of the breaker protecting the feeder?
 
  #11  
Old 07-01-04, 10:13 AM
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#8 copper is acceptable for a 100-amp feeder.
 
  #12  
Old 07-01-04, 11:55 AM
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Don't anybody take PATTBAA's statement out of context. He is talking about the EGC only.
 
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