subpanel installation

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  #1  
Old 06-21-05, 10:01 AM
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I just moved to a place that has a very large "garage / barn" (4 cars + 2 stalls) and need to upgrade the electrical in it. In my previous house, I ran a 100 am sub and did a fair amount of electrical, but this one has me wondering...

The way the "barn" is wired currently, there is a 2-wire+ground Romex 6AWG line from the main 200amp panel in the house that goes through the attic and into the basement. There it is "reduced" in a JB to 10-2+g romex that feeds it to the barn in PVC conduit. The main panel has a 30amp DP breaker feeding the 6AWG romex, but THERE IS NO NEUTRAL!!. In the barn, the ground and neutrals are together on the bus bar, and there is an additional ground rod sunk behind the structure. There are 2 15A CBs in the sub, feeding lights and a few outlets only.

Was this code acceptable in 1988? The house wiring is top notch and probably the cleanest / neatest main panel I have ever seen. CH box, everything labeled. Can't figure out why they would only run 10awg out to the barn unless it was a cost issue, nor do I get the lack of neutral.

So, I plan on pulling the 10 and running copper 4AWG THHN (3 conductors + ground total) and protecting it with a 60A DP CB. (distance to barn is ~100 feet). Is there any reason I would not also replace the 6AWG romex?

Thanks in advance!!

-Tony
 

Last edited by John Nelson; 06-21-05 at 11:48 AM. Reason: New threads are cheap
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  #2  
Old 06-21-05, 11:27 AM
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Yes, replace the #6 nm. You must have a separate neutral. Also note that #6 romex is only good for 55 amps. In the barn make sure the neutrals are on an isolated neutral bar and separated from the grounds which will be on a separate ground bar which is bonded to the panel.
 
  #3  
Old 06-21-05, 12:49 PM
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Your PVC conduit needs to be at least 1" to get the #4 conductors through within code.

The bare ground wire in your existing setup is acting as the neutral; what you really have is no separate ground to the barn. So long as there are no other metal pathways to your barn, you do not need a separate ground to the building, although it is still a really good idea to do so.

Nonetheless, your existing wiring is wrong because the neutral is a bare wire.
 
  #4  
Old 06-21-05, 01:26 PM
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Your feeders could consist of the following: 2-#4 AWG copper hot conductors. 1-#6 AWG copper neutral conductor and 1-#8 AWG copper equipment grounding conductor (actually, you could use a #10 AWG copper equipment grounding conductor per NEC 2002 Table 250-122).
 
  #5  
Old 06-21-05, 02:38 PM
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Thanks guys.

Conduit is 1 1/4" PVC SCH80, so I should be good there.

Technically, there is another metal pathway - phoneline in the same conduit.

I'll definitely follow the advice and get it inspected.

-TB
 
  #6  
Old 06-21-05, 03:08 PM
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You will fail inspection with a phone line in that conduit. It is a strict no-no to run telephone (or anything other than power) and power in the same conduit or junction box. Pull that phone line out and investigate some of the great wireless products out there assuming you don't want to dig another trench just for phone.

Telephone wire counts as a metal pathway requiring a seperate ground.
 
  #7  
Old 06-22-05, 04:45 AM
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Yeah, I kind of figured it was a no-no. I don't need a wired phone to the shop anyhow.

Anyone have a rec for a good wireless intercom or phone jack?

I still think it is weird that all this passed inspection in '88...

In order to not have to run new wire all the way back to main panel (which means up and into attic, then down into attached garage), I think I will start out from the 100A subpanel that is in the basement fairly close to the conduit stub - it is wired with a neutral!

The conduit is 2" Sch80 PVC (measured last night). I will probably pull #4 copper THHN/THWN for hots & neutral, plus #6 green for ground.

Thanks again for the advice!
 
  #8  
Old 06-22-05, 07:48 AM
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Originally Posted by comgenboy
I still think it is weird that all this passed inspection in '88...
Whomever installed the orignial stuff probably changed it after the inspector left.
 
  #9  
Old 07-01-05, 04:14 AM
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Follow ups

Most of my supplies have been purchased, and permit obtained.

Question 1 - Can the panel in the detatched structure be on a wall immediately next to the entry door? Eg, the panel will be covered by the door when it is held open, but will be accessable otherwise.

#2 - (I think I know the answer...) THHN needs to be totally enclosed in conduit from the feed to the subpanel? Or can it be protected by wood / drywall in the short transition from sub to conduit?

#3 - Decided the 15cents up charge for #2 wire was worth it to go with a 100 amp sub. Run will consist of 2x#2 hots, #2 neutral, #8 ground. I will also have 2 ground rods at the barn.

#4 - Running a 100 amp sub off of another 100 amp sub is okay as far as I recall, yes?

THANKS AGAIN
 
  #10  
Old 07-01-05, 07:17 AM
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(1) Yes, as long as it has the required clearances (30" wide, 36" in front, 6'6" headroom).

(2) Conduit all the way.

(3) Okay.

(4) Okay.
 
  #11  
Old 07-01-05, 09:23 AM
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Does the 30 inches measure from each end f the panel, or is it just clearance in general to have access to it?

The 36 is there when the door is closed, so that should be good to go.

Thanks again!
 
  #12  
Old 07-01-05, 09:47 AM
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I believe the panel can be located anywhere within the 30" space. The idea is to have enough room to safely access and work in the panel. Which leads me to a question... For a new thread.
 
  #13  
Old 07-01-05, 09:48 AM
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The 30 inches the the total side-to-side clearance. The panel may be on the left side of that 30", on the right side of that 30", or in the middle of that 30". The panel door must be able to open at least 90 degrees.
 
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