Subpanel: Neutral Bus & Ground Bus

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  #1  
Old 08-17-06, 02:06 PM
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Subpanel: Neutral Bus & Ground Bus

Current Situation: I have a main panel in a detached garage, from it I have a 4 line feeder (running underground) to a subpanel in my house. My subpanel currently only has one bus which I'm assuming would be a neutral & ground bus combo. The house does not currently have any ground wires on any of the the circuits (all outlets are two prong). Right now two of the four wires (the neutral and the ground) from my 4 line feeder attach to opposite ends of this one combo bus.

Question/Scenario: I am going to re-wire the entire house to include ground wires on all circuits (replace all two prong outlets with three prong and all 12/2 & 14/2 wire with 12/3 & 14/3 wire). My question is do I need to make changes so that I end up with a neutral bus and a ground bus seperated from each other (not connected in any way)? From what I have read, it sounds like this is what I have to do, but I wanted to check. If this is what I do, I assume I would keep the existing bus bar as my neutral, remove the 4th feed wire (ground wire) from this existing bus bar and attach it to a new bus bar, which would then become by ground bar. I would attach all neutral wires from my circuits to the neutral bus bar and all ground wires to the ground bus bar. Are there any rules about how and where to attach this new ground bus bar? I don't have alot of room in my subpanel box, but I suppose I could make room to attach it perhaps to one of the sides or the back (can I do that???). Also, do I then need to run a wire from the ground bus bar to a cold water line or is the ground already created by attaching the 4th feeder line from the main panel? Any comments/replies/suggestions would be greatly appreciated.
 
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  #2  
Old 08-17-06, 03:26 PM
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Originally Posted by calizeus
Current Situation: I have a main panel in a detached garage, from it I have a 4 line feeder (running underground) to a subpanel in my house. My subpanel currently only has one bus which I'm assuming would be a neutral &
ground bus combo..
Apparently whomever installed the wiring from the garage to the house used a 4 conductor cable and just connected the
neutral and ground to the same terminal.

Originally Posted by calizeus
Question/Scenario: I am going to re-wire the entire house to include ground wires on all circuits (replace all two prong outlets with three prong and all 12/2 & 14/2 wire with 12/3 & 14/3 wire). My question is do I need to make changes so that I end up with a neutral bus and a ground bus separated from each other (not connected in any way)?
Yes. The neutral and ground are only connected in the main panel. Suggest you use only #12 thru out the house.

Originally Posted by calizeus
From what I have read, it sounds like this is what I have to do, but I wanted to check. If this is what I do, I assume I would keep the existing bus bar as my neutral, remove the 4th feed wire (ground wire) from this existing bus bar and attach it to a new bus bar, which would then become by ground bar. I would attach all neutral wires from my circuits to the neutral bus bar and all ground wires to the ground bus bar.

Since you are going to all this trouble I would suggest that you remove the old panel and install a new one. The neutral and ground bus bars are already seperatred.

Originally Posted by calizeus
Also, do I then need to run a wire from the ground bus bar to a cold water line or is the ground already created by attaching the 4th feeder line from the main panel? Any comments/replies/suggestions would be greatly appreciated.
That should have been done at the main panel. If its not done,
get it installed.
 
  #3  
Old 08-17-06, 03:26 PM
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Removed double post.
 
  #4  
Old 08-17-06, 03:48 PM
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your reply is great, thanks.

The only question I have remaining (and this is only because I do not want to replace the entire panel), is about installing the new bus bar in the subpanel. Can I just drill holes and/or use existing holes in the side of the panel and attach the new bus bar to the stud through these holes (so that it would end up being stud, then metal siding of panel, then bus bar - inside of the panel in other words)? I would then attach the 4th feed wire to this bus bar, correct? I assume I would want to make every effort to make sure that none of my ground wires touch the neutral bus, correct?

Oh, and just to clarify, on the main panel the shared neutral/ground bus does appear to be grounded, so I don't need to run a wire to a cold water line from the ground bus on the subpanel? I think that is what you are saying, just wanted to make sure.

Thanks again
 
  #5  
Old 08-17-06, 04:19 PM
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You must use an approved ground bar, which will attach to your panel. You cannot drill your own holes.

If the idiot who wired this electrically connected the existing bar to the panel using the green screw, then you need to remove the screw and make sure that the neutral bar is NOT electrically connected to the panel.

Your panel must be properly grounded using a grounding bar. Further, incoming water lines MUST be connected as well. These connections go to the GROUND bus, not to the neutral buss. The neutral buss must be floating, not grounded.
 
  #6  
Old 08-18-06, 08:24 AM
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Thanks for the reply.

I have a few questions from your post. Unfortunately, I'm not by the panel and will not be able to look at it until this evening, but I'll do my best from memory.

"You must use an approved ground bar, which will attach to your panel. You cannot drill your own holes."
My panel has the Stablok breakers from Federal Pacific, so I guess I have a Federal Pacific panel? Do you know where I can find an approved ground bus bar for Federal Pacific panel?

"If the idiot who wired this electrically connected the existing bar to the panel using the green screw, then you need to remove the screw"
I don't recall seeing any green screw, but I'll have to look tonight to make sure.

"make sure that the neutral bar is NOT electrically connected to the panel."
Can you please clarify? Does these mean that the metal on the bar cannot be touching the metal box?

"incoming water lines MUST be connected as well. These connections go to the GROUND bus, not to the neutral buss"
Can I do this by running a heavy copper wire, say a #6 or #8, to ANY incoming water line? You mentioned lines, I don't have to connect to every incoming line do I?

It seems like there is alot of conflicting information out there on grounding the subpanel. Some info says to ground the subpanel ground bus bar(to a water line for example) as well as connect the 4th feeder line to the ground bus bar. Other info says do not connect the ground bus bar to any water lines, buried rod, etc., but to only connect the 4th feeder line (from the main panel).

I look forward to and appreciate any feedback / responses.
 
  #7  
Old 08-18-06, 08:50 AM
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Replace the panel. Federal Pacific panels need to be replaced. Period.

I suggest that you pay for and have an electrician install the panel. A panel this important is NOT something to mess around with.

Your incoming water line, if it is metal, must be connected (within five feet of where it enters the house) to the ground buss in the panel. If the incoming water line is plastic, then any metal water pipes in your house must be BONDED to the ground buss in the panel. Regardless, you still need additional grounding. This is usually accomplished with a ground rod.

Since this panel in your house is a sub panel, the ground buss and the neutral buss MUST be separated. The ground buss MUST connect to the metal panel box. The neutral buss must NOT connect to the metal panel. Usually a green screw is provided with a new panel that when tightened makes the connection between the buss and the metal panel, making it either a combines ground and neutral buss (for main panels) or a ground buss for (sub panels).

A sub panel in the same building as the main panel is not grounded except via the ground wire from the main panel.

A sub panel in a detached building is always grounded to a proper external grounding means (which usually means any water pipes and a ground rod).
 
  #8  
Old 08-18-06, 09:15 AM
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Thank You. You definitely clarified the whole grounding the subpanel discrepencies.

Does the FPE panel have to be replaced for code reasons or for safety reasons? I've read about the safety issues on them, but didn't know if they would pass a code inspection. If I do have to replace it, I'd like to move it. I would have no problem extending the circuit lines to the new panel. However, how can I extend the 4 feeder lines from the main panel without re-running new lines? I have a brick house, and the lines come into the brick, so just moving where they come into the house is not much of an option. What type of panel would you recommend that would be most economical as well as trusted?

Also, is CONNECTED the same as BONDED? You mentioned that copper water lines coming into the house must be CONNECTED to the ground bus, but if the are plastic, that any metal water pipes must be BONDED to the ground bus. If the terms are not interchangeable, then what is the difference?

Thanks!
 
  #9  
Old 08-18-06, 10:37 AM
Join Date: Jul 2006
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FPE panels need to be replaced due to safety issues. The breakers will not trip.

I like Square D for replacement panels. Their breakers have QO or quick open contacts. Square D has 2 different lines the QO and Homeline. The QO, in my opinion is the best, but the Homeline will work just fine in residential applications. The Homeline line also have the quick open contacts in their breakers.

The green ground screw Racraft is referring to in typically at the top of your neutral bus. Not all panel manufacturers use the screw, sometimes there is a metallic strap that is offset and connects directly to the neutral bus and the panel frame.

I recommend hiring a qualified electrician to properly install your subpanel and complete the grounding. The finer points of proper grounding are not the simplest to understand and not the place for a DIYer.
 

Last edited by gilchrist-elect; 08-18-06 at 12:40 PM.
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