Subpanel question

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  #1  
Old 08-21-04, 07:33 PM
iknownothing
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Subpanel question

Hello. I need to install a subpanel in my house because I am out of circuits. I installed a 100amp 2 pole in the main panel to feed the new subpanel.
Questions:
1- Do I install a ground wire from the subpanel ground lug to the main panel ground lug?
2- Can I install #3 conductor from the 2-pole breaker to the subpanel main lugs? (100 amp breaker)
3- Do I install the neutral from the subpanel to the main panel neutral bar?
4- If I install all 4 wires, does that then mean I cannot bond the neutral and ground lugs together? In other words, do not install that green screw that came with my box?
5- I also installed a subpanel in my polebarn (not attached to my house and no metallic connection between the house and polebarn so I ran three #3 conductor to that panel. That panel will connect to a 100amp 2 pole breaker in the new subpanel in the house. Since I only have three conductors going out to the barn, do I need to install that green screw in the panel in the barn?
If so, where does it get installed?

Thank you for your help.
Brian
 
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  #2  
Old 08-22-04, 05:47 AM
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To feed your sub panel, you need four wires. Two hot wires, a neutral and a ground wire. At the sub panel you need to keep the neutral and ground wires separate. Throw away the green screw which would be used to bond the neutral bar to the panel, and install a separate ground bar for the grounds which will be binded to the panel.

However, before you do this, have you considered tandem or dual breakers? They are cheaper than a sub panel.
 
  #3  
Old 08-22-04, 07:27 AM
iknownothing
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The electrical inspector in my township said tandem breakers are not allowed even thow my box supports them. He said I needed a subpanel.

You mention getting a seperate ground bar for the subpanel. Where do I install that? I saw one site where the guy mentioned removing the strap between the neutral and ground bars. http://www.electrical-online.com/how...s/subpanel.htm

What about the polebarn coming off the new subpanel? Does that need to have neutral and ground seperated by attaching a seperate ground bar? Or as that site suggested, remove the bar attaching the two? (The polebarn panel has two grounds connected to grounding stakes 6 feet apart.)

Thanks again for your help!
Brian
 
  #4  
Old 08-22-04, 10:15 AM
iknownothing
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I put a drawing up online so you can see what has been suggested to me. If someone can confirm that this is indeed the correct approach, I would appreciate it very much.

http://24.247.104.134:8100/basement/...anelconfig.rtf

Thanks again!
Brian
 
  #5  
Old 08-22-04, 04:35 PM
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Your picture indicates that you have chosen not to run a grounding wire from the house subpanel out to the pole barn. This is okay as long as there is no other metallic path between the buildings (no phone line, no water line, no gas line, no TV cable). If you stick with this decision, then you absolutely must bond the neutral and grounding bars in the pole barn panel. To do otherwise would be very unsafe.

However, you might consider instead running a grounding wire from the house subpanel to the pole barn. This is a somewhat better installation, and it gives you the option of adding a metallic path in the future. If you do so, however, then leave your neutral and grounding bars in the pole barn isolated.
 
  #6  
Old 08-22-04, 06:22 PM
iknownothing
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Thank you very much for your help John.

Will you confirm that what I was told is correct about seperating the neutral and ground bars in the house subpanel. If I do indeed need to do that, is it as simple as purchasing a new ground bar and installing it in the panel as I indicated in my drawing? Is everything else in my drawing correct?

Thanks again!
Brian
 
  #7  
Old 08-22-04, 06:26 PM
iknownothing
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Sorry, I also meant to ask about bonding the polebarn as you suggested. Does that mean I need to use that green screw that came with the box or not? If so, where does it go? I am confused about the green screw. Is it used when you need to bond the neutral to the ground bar or not? What is it's purpose exactly?

Thanks,
Brian
 
  #8  
Old 08-22-04, 07:04 PM
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In the house subpanel, the neutral and grounding bars must be isolated, in all cases. So throw away the green bonding screw for this subpanel, and purchase a grounding bar kit (if the subpanel didn't already include a separate grounding and neutral bars).

At the pole barn, assuming you wire as your diagram indicated without a grounding wire from the house, then install the green bonding screw such that it bonds the neutral bar to the case (you ohmmeter can confirm when you've got it right). You may then either use the neutral bar for both neutral and grounding wires, and/or buy a separate grounding bar.
 
  #9  
Old 08-23-04, 04:55 AM
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Search for previous threads on subpanels. This is one of the most frequently asked questions.

Very briefly: the ground and the neutral _must_ be connected together, but in _one_, and _only_ one location. So in your _main_ panel, you electrically connect the ground and neutral. (You use the green screw in the neutral bar, you wire your ground wires to the neutral bus, etc.) In all other subpanels in your home, you electrically _isolate_ the ground and neutral.

The one exception to the 'one and only one' bond is a _detached_ structure, eg your pole barn. If you have nothing metallic between the two structures; no metal water pipe, no phone wires, no fence, no nothing, then you _may_ install the subpanel in the pole barn is if it were a main panel. In this case you have to do everything like a main panel (bonding, grounding, etc). You may choose to use a standard 4 wire subpanel connection, with separate ground and neutral, isolated from each other. You still have to add the ground rods at the detached structure.

Which is better depends upon numerous subtle points, but the 'no metallic structures' rule generally makes the 4 wire approach the only one allowed. But if you have no other metallic structures, than you can use the three wire approach if you wish.

Note that what you drew is neither of the two allowed approaches, and is in fact the most dangerous setup you could have. Do a new drawing showing which approach you intend to use, and we will tell you if it is correct.

-Jon
 
  #10  
Old 08-23-04, 02:13 PM
iknownothing
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Here's what I understand needs to be changed per your suggestion (indicated in red):

http://24.247.104.134:8100/basement/...nelconfig2.rtf

My understanding of what you mean by "dangerous" is that the ground and neutral were not shown as bonded on my drawing??

Thank you again for your help!
Brian
 
  #11  
Old 08-23-04, 02:41 PM
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Yes, that is now correct.
 
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