Ground for detatched garage

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  #1  
Old 07-17-07, 09:57 PM
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Ground for detatched garage

Ok -- as simple as I can.
!00 amp service to main panel- 30 amp 2 pole feeding a 30 amp two pole in a detatched garage. (30 amp , 2 space load center) This then feeds my subpanel-(100 amp, 6 space, Main lug) .

Installed the ground buss kit in the subpanel, "Unbonded" the neutral , Drove a ground rod. Now the question....
The 30 amp breaker in the garage would be acting as a "MAIN" breaker for my main lug panel. Subpanel neutral and grouds are isolated from each other. In this "Main Breaker Box" (In the garage ) the neutral and ground are "BONDED". I dont see any "Dimples " to install a ground buss, Nor do I see any way to "UNBOND" the neutral buss from the box. What to I do , or should I say where do I put the wire from the Ground Rod? Main breaker , or subpanel?
 

Last edited by Unclediezel; 07-17-07 at 09:58 PM. Reason: misspell
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  #2  
Old 07-17-07, 11:06 PM
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I've never not seen a way to unbond the neutral buss or install a ground buss. Many you can give us the make and model number of the panel you bought? Where did you get it?
 
  #3  
Old 07-18-07, 08:21 AM
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To make sure I'm clear on this: you have a 2-space load center which is being fed by 30A, #10 wires from the main and subsequently feeds another subpanel down the line via 30A, #10 wires. In this two space load center, the ground and neutral cannot be isolated?

First off, your sub-subpanel (100A) sounds correct as-is; don't change anything there.

At the 2-pole load center in the detached garage, use the built-in ground/neutral bar as the ground bar. This is where the incoming and outgoing grounds land and the GEC conductor to the ground rod. Splice the two #10 whites together using an insulated set-screw block. This effectively isolates them from the ground.

The other option is to just replace the two space load center with a different model that has isolated ground and neutral bars. A small box like that should only be about $30.
 
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Old 07-18-07, 09:01 AM
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Doesn't it seem like you have one more box than you need? Why do you even have the two-space load center? Can't you just put that same breaker directly in the subpanel? Then you wouldn't have this problem.

You didn't say whether you ran three or four wires between the two buildings. That's an important detail.
 
  #5  
Old 07-18-07, 04:04 PM
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Originally Posted by John Nelson View Post
Doesn't it seem like you have one more box than you need? Why do you even have the two-space load center? Can't you just put that same breaker directly in the subpanel? Then you wouldn't have this problem.
This setup was in the garage when I bought the house 6 months ago. The subpanel in the garage is a square d 100 amp , 6 space 12ckt Main lug box. The 2 space is actually being used as the disconnect , for the "More than 6 breakers in a panel , without a main breaker" rule. I dont mind spending an extra 25 or 30 bucks on something that makes sense to me, so I'll probably just get a newer style box that I dont have to spend 4 hours staring at it to understand it, before I can use it.

To answer your question John, its a four wire feed from the Main panel in the house. then to the 2 space "Disconnect, and on to the sub. The way I understand it , A subpanel has Ground and neutral Isolated from each other.(Which in effect , would be EVERYTHING downstream of my MAIN SERVICE PANEL). I installed a Ground electrode for the detatched building, conductor is alrerady run , but I'm confused on where to put it.
 
  #6  
Old 07-18-07, 04:16 PM
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Originally Posted by ibpooks View Post
To make sure I'm clear on this: you have a 2-space load center which is being fed by 30A, #10 wires from the main and subsequently feeds another subpanel down the line via 30A, #10 wires. In this two space load center, the ground and neutral cannot be isolated?

< EXACTLY

At the 2-pole load center in the detached garage, use the built-in ground/neutral bar as the ground bar. This is where the incoming and outgoing grounds land and the GEC conductor to the ground rod. Splice the two #10 whites together using an insulated set-screw block. This effectively isolates them from the ground.

< Just for theory-(I wouldnt actually do this) take the white wires off the buss and wire nut them together, and use the buss for grounds?

The other option is to just replace the two space load center with a different model that has isolated ground and neutral bars. A small box like that should only be about $30.
< Probably the easiest way out.... But ..When all is done , does the GEC have to connect to the sub,(100a) or do the feeders take care of grounding the buss in the sub?
Thanks much guys.
 

Last edited by Unclediezel; 07-18-07 at 04:19 PM. Reason: misspell
  #7  
Old 07-18-07, 04:27 PM
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In this "Main Breaker Box" (In the garage ) the neutral and ground are "BONDED". I dont see any "Dimples " to install a ground buss, Nor do I see any way to "UNBOND" the neutral buss from the box. What to I do , or should I say where do I put the wire from the Ground Rod? Main breaker , or subpanel?
I expect that the main breaker box is listed as "suitable only for use as service equipment". These panels have no way to "unbond" the neutral. You need a panel that is listed as "suitable for use as service equipment". This type of panel will come with a "main bonding jumper". You would throw the main bonding jumper away and land the grounding electrode conductor on the ground bar along with the equipment grounding conductor from the power source.
 
  #8  
Old 07-18-07, 04:45 PM
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Originally Posted by resqcapt19 View Post
I expect that the main breaker box is listed as "suitable only for use as service equipment". These panels have no way to "unbond" the neutral. You need a panel that is listed as "suitable for use as service equipment". This type of panel will come with a "main bonding jumper". You would throw the main bonding jumper away and land the grounding electrode conductor on the ground bar along with the equipment grounding conductor from the power source.
I just left SQ D's website and You are absolutely correct.Ive never seen this before. I'm off to buy a new box. When I remove the jumper , there will be 2 seperat buss bars, one bonded to the case and one not? The electrode conductor lands in my new box...does it also have to make its way to my subpanel?, or are my existing connections sufficient?
 
  #9  
Old 07-19-07, 04:15 AM
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Originally Posted by Unclediezel View Post
The electrode conductor lands in my new box...does it also have to make its way to my subpanel?, or are my existing connections sufficient?
The grounding electrode stops at the main disconnect...just the EGC goes on to the subpanel.
 
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