Subpanel Bond

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  #1  
Old 04-18-14, 11:01 AM
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Subpanel Bond

I have a subpanel in garage. There is a egc bus installed and the neutral bus. As far as I can tell, I do not see a bonding screw or strap on the neutral bus bar (hence they should be separated).

I need to do some testing to assure.

A few weeks ago I removed all the branch neutrals from the busbar and just the feeder neutral was connected and there was no continuity between the metal box and the neutral bus bar.

Today I was in the box again, all of the branch neutrals connected to neutral bus bar, and I was getting continuity between the box and the neutral bus.

So its making second guess myself.... is my initial test correct?
 
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Old 04-18-14, 11:16 AM
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A few weeks ago I removed all the branch neutrals from the busbar and just the feeder neutral was connected and there was no continuity between the metal box and the neutral bus bar.
That is incorrect. Since your neutral and ground wires are connected at the main panel...... there will always be continuity between neutral and ground.
 
  #3  
Old 04-18-14, 11:36 AM
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Just to clarify, theres no egc on these circuits. The egc bus is connected to a ground rod. I wanted to assure that the gec bus and the neutral bus were NOT bonded together.

The only other test I did to assure they were not bonded together was what I describe in the other post... I also had the subpanel loaded up. I measure about 1VAC between the ground bus and the neutral bus. I assume if they were bonded, I would have read 0VAC?

What else can I do to assure that the Ground buss and the neutral buss in my subpanel are not bonded together?
 
  #4  
Old 04-18-14, 01:51 PM
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How many wires feed this subpanel? 3 or 4? I'm reading it as 3 and that there is NO separate ground wire run to the main panel. When was it installed?

On a 3 wire feed, you MUST bond the neutral and ground busses together. Ref: NEC 250.32(b)(2)

On a 4 wire feed you DO NOT bond them.

Both require a ground rod in a detached structure.
 
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Old 04-18-14, 02:41 PM
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How many wires feed this subpanel? 3 or 4? I'm reading it as 3 and that there is NO separate ground wire run to the main panel. When was it installed?

On a 3 wire feed, you MUST bond the neutral and ground busses together. Ref: NEC 250.32(b)(2)

On a 4 wire feed you DO NOT bond them.

Both require a ground rod in a detached structure.
3 wire. rigid conduit between the panels.... they need to be unbonded. There is a ground rod and the only thing that attaches to the ground buss in sub is the gec attached to that rod. The branch circuits are all in metal conduit as well.
 
  #6  
Old 04-18-14, 03:36 PM
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Just to clarify, theres no egc on these circuits.
Yes there is, the rigid conduit, if it's in good condition.

You are bonded back in the main panel.
 
  #7  
Old 04-18-14, 04:19 PM
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good catch... I meant to say separate grounding wire (egc) in the boxes... the conduit is the egc on these circuits.

You are bonded back in the main panel.
Right, but in the subpanel the egc buss and the neutral buss must be unbonded. Just putting it out there for clafification sake.....

So question remains:
What else can I do to assure that the Ground buss and the neutral buss in my subpanel are not bonded together?
 
  #8  
Old 04-18-14, 05:31 PM
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How about removing the feed from the neutral bus at the subpanel. With that done you'll isolate it from the main panel.

Then measure continuity from the neutral bus to the ground bus. It should be open.
 
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