Upgrading panel in detached garage/shop

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  #1  
Old 03-03-14, 11:52 AM
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Upgrading panel in detached garage/shop

Hi all,

In preparation for a new cabinet saw purchase, I need another 240V circuit in my shop. There is no space on the current (small) subpanel out there that was installed by the previous owner, and it's also way undersized for a woodshop anyway, so I'm taking this opportunity to upgrade the service. I'm confident in my electrical abilities, but wanted to run a couple of things by you guys. The current panel is a small, 4 slot breaker fed through a 30amp double pole breaker from the main panel in the house. My garage is detached and has its own grounding rod. It is fed by three 10gauge wires via PVC conduit from the house about 100 feet (i.e., no ground wire, just two hots and a neutral). My plan is to upgrade to 60amp service on a 125amp subpanel that my father in law had left over from a previous job.

I have two questions:

1. This first one is more of an FYI for myself. The current panel is fed, once again, by three wires. I understand that this was allowed by the NEC until 2008. However, the neutral and ground bars are not bonded in the subpanel. This is incorrect, right? The neutral wire coming from the house is connected to the neutral bus in the subpanel, and the grounding wire coming from the garage's grounding rod is connected to the ground bar in the subpanel, but they are not bonded. My understanding was that NEC allowed the three wire feed as long as the neutral and ground bars were bonded in the subpanel (so that stray current had a way to return to the main). Again, this question is just for my own education.

2. My second question is just whether my plan makes sense and is correct. Here it is:
  • Pull four new wires to the garage. Three 6gauge conductors (2 hots, 1 neutral), and one 10gauge grounding wire that is connected to the ground bar in the main.
  • Mount my new 125amp subpanel in the garage.
  • Backfeed a 60amp, double pole main breaker in my subpanel using the 2 hots from the house (I have the hold down kit for the main breaker, and backfeeding is allowed on this panel).
  • Change the breaker in the main panel feeding this subpanel to 60amp double pole.
  • Change the breaker in the main house panel feeding this panel to 60amp double pole.
  • Connect the neutral wire from the house to the neutral bus in the subpanel.
  • Connect the grounding wire from the house to the ground bar in the subpanel.
  • Connect the grounding wire from the garage grounding rod to the ground bar in the subpanel.
  • Break the bond between the neutral and ground bars in the subpanel.

Does this all make sense?

Thanks a lot in advance.
 
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  #2  
Old 03-03-14, 11:56 AM
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The current install was not correct since the neutral was not bonded to the ground.

Other than that your plan sounds solid.
 

Last edited by ray2047; 03-03-14 at 12:05 PM. Reason: Typo
  #3  
Old 03-03-14, 12:06 PM
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Thank you very much. One follow up question. Since I'm going with the 4 wire feed (see attached picture), should the branch circuits on the subpanel have their bare grounding wires connected to the neutral bus in the subpanel or to the grounding bar? In other words, should the equipment grounds be going to the GES of the garage or heading back to the main via the neutral bus?

(The separate grounding is what has me confused. Is the grounding bus on the subpanel only there to diffuse static charges that build up on the subpanel case?)

(Edit - forgot to attach picture)
 
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  #4  
Old 03-03-14, 12:07 PM
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should the branch circuits on the subpanel have their bare grounding wires connected to the neutral bus in the subpanel or to the grounding bar?
No, in a subpanel grounds only go to the ground bar and neutrals only to the neutral bar.
 
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Old 03-03-14, 12:16 PM
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The EGC from the branch circuits will go to the ground bar.
 
  #6  
Old 03-03-14, 12:33 PM
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Thanks, sorry one more question. I appreciate all the quick responses:

I can only seem to find 6AWG THHN that is either black or white. Is it ok to use black for both hot conductors and use colored electrical tape at the termination points to differentiate them?

I thought I remembered reading somewhere that you could only do that if it were part of a wire assembly (e.g., romex, as in a 240V circuit).
 
  #7  
Old 03-03-14, 12:37 PM
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Hmm, I just found Wire and Cable To Go | Copper Building Wire, Portable Cord, Industrial Cable. What a great site! Looks like I can order any color 6AWG THHN that I want from there by the foot.
 
  #8  
Old 03-03-14, 12:59 PM
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There is no need to differentiate between the two blacks.
 
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Old 03-03-14, 04:30 PM
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Hmm, I just found Wire and Cable To Go | Copper Building Wire, Portable Cord, Industrial Cable. What a great site! Looks like I can order any color 6AWG THHN that I want from there by the foot.
You need THWN in the conduit. It's considered a wet location.
 
  #10  
Old 03-03-14, 06:15 PM
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Most THHN is dual rated THHN/THWN.
 
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