Sub panel wiring

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  #1  
Old 01-19-12, 12:02 AM
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Sub panel wiring

I changed out a sub panel in a horse barn for a friend of mine. The original panel was pretty ratty and too small to add any more circuits.

The panel is fed via a three wire feed. Two hots and a neutral.
Neutral and grounds from the branch circuits shared the same bus bar.

I copied this in the new panel. But I added a ground rod.
Looking around online I see that a three wire feed was/is ok, other places say that I need a four wire feed.

Does the three wire feed have to be upgraded when changing out the sub panel?

Ive included three pictures. Two are in process pictures of the new sub panel. The last is of the main panel for the farm. The transfer switch under it transfers incoming power from the meter to a welder outlet. With no over current protection.

The junction boxes are so I could have enough wire in the new panel to tie in the neutrals and grounds.

The panel is fed via a 40 amp breaker. I should also add that the wires feeding the panel are not rated for direct burial and they are buried right in the dirt. The conduit ends a few inches into the ground.





 
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Old 01-19-12, 01:27 AM
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EXTREMELY DANGEROUS!

I'm sorry to say that the wiring needs to be changed. You need to use three conductor plus ground wire. You must not bond the neutral and ground bus bars in a subpanel. They must be individually ran back to the main panel. The panel should have a way to remove the connection between the two bus bars to keep them separate, and all the neutrals must be kept on one and all the grounds on the other.

The only place the neutrals and grounds may be connected is at the main panel.

Current should always be returning through the neutral, except for a fault scenario. When you bond these at a subpanel, you're effectively turning those grounds into neutrals, thus allowing current to return through anything bonded to your ground wires on the way back. Even worse, if your neutral path fails, all current is returning on a bare ground wire.

Look up contact voltage. Many injuries and deaths.

Mod notes: Existing 3 wire feeder are allowed to continue in usage. There should not be another metallic path between the two buildings.

The neutral is again bonded in the subpanel.
 

Last edited by pcboss; 01-19-12 at 10:01 AM.
  #3  
Old 01-19-12, 01:54 AM
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Ok, my next question. This sub panel feeds another sub panel. It is fed via a 20 amp 120v circuit. It is a fuse panel. A hot neutral and ground. The ground feeding the second sub panel is tied to the neutral wire as soon as it leaves the barn. Then where the power feeds into the second barn the neutral and grounds are tied together again. Before the wire enters the fuse box. So undo that mess also?

This is where I got some of my info.
Garage Sub Panel - Int'l Association of Certified Home Inspectors (InterNACHI)

3-wire feeds to existing detached buildings - InterNACHI Inspection Forum
 

Last edited by OldRedFord; 01-19-12 at 04:08 AM.
  #4  
Old 01-19-12, 06:11 PM
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I'll type a longer reply soon, but let me ask two quick questions for now. They won't really change my answer, but I'll be able to give more specific relevant info.

Did you just change out the subpanel, or was it a while ago? I've assumed the 1/1/2007 date in the pictures was a default camera date, but I see the third picture is marked 1/25/2007.

And, which state is this in?
 
  #5  
Old 01-19-12, 08:37 PM
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On the topic of your install. If this is indeed a horse barn, then you should review NEC before continuing. This is a lot more involved than you know. Personally, I would never keep a three wire system for any animal housing.
 

Last edited by SeaOn; 01-19-12 at 08:59 PM.
  #6  
Old 01-20-12, 05:09 AM
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While nowadays you need a 4 conductor feed (for 120/240 volts) between two buildings, the 3 conductor feed has been permitted in the past because it is a horse of a different feather (no pun intended).

With neutrals and grounds bonded at the subpanel, and no ground wire in the feed cable, return current is not sharing neutral and exposed ground wire (except for any leakage through the earth via the ground rod near and bonded to the outbuilding subpanel).
 
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Old 01-20-12, 07:53 AM
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With neutrals and grounds bonded at the subpanel, and no ground wire in the feed cable, return current is not sharing neutral and exposed ground wire (except for any leakage through the earth via the ground rod near and bonded to the outbuilding subpanel).
Moot point though. The rules were changed for safety reasons and current rules must be followed for this installation.
 
  #8  
Old 01-20-12, 11:39 AM
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-Our State adopted the four conductor rule far before the NEC. They went backwards and forwards at one time, but finally got it right.

@ Allan,

because something was accepted before, doesnít mean itís safe now. The reason for new code adoptions, are to correct,and make safe old ones. To add: Many things are acceptable, but I go above code when I donít accept it. Example: I do not believe in using metallic conduit in place of an equipment grounding conductor.
Personally, I believe the install I see is unsafe> A few questions: 1. Type of cable being used. 2. If receptacles are being used, are they protected. 3. Why isnít the light fixture protected. Etc etc..
 
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Old 01-20-12, 11:47 AM
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And we haven't even delved deep into explosive environment requirements yet though Seaon has raised it with the light.
 
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