Grounding a sub-panel

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  #1  
Old 04-22-06, 07:14 AM
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Grounding a sub-panel

In another thread on grounding a sub panel, this comment was made.

Whereas it is always correct to land EGCs and GECs on the ground bar in every panel everywhere, number of feeder wires doesn't change this.

This is not correct. Many localities require the GEC be terminated to the neutral buss if a 3 wire feed is used to power a sub panel, just as they do at the main panel. It doesn't matter that the 2 busses are tied together, the idea is to keep the number of connections to a minimum. Many utilities also require this.

2005 NEC©®

250.24 Grounding Service-Supplied Alternating-Current Systems.
(A) System Grounding Connections. A premises wiring system supplied by a grounded ac service shall have a grounding electrode conductor connected to the grounded service conductor, at each service, in accordance with 250.24(A)(1) through (A)(5).
(1) General. The connection shall be made at any accessible point from the load end of the service drop or service lateral to and including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means.

I think that the language here indicates an NEC preference for a direct EGC to neutral, or grounded conductor, connection.
 
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Old 04-22-06, 08:05 AM
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(1) General. The connection shall be made at any accessible point from the load end of the service drop or service lateral to and including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means.
I agree with your interpretation of this, Bill. The text makes it pretty clear that it is to land with the neutral on a service. I believe that the purpose is to more thoroughly ensure that voltage imposed by line surges and unintentional contact with high voltage lines will be connected to the grounding electrodes at any structure served.

One edit you may want to make for clarity is your last sentence, I believe you wrote "EGC" when you meant "GEC."
 

Last edited by Rocky Mountain; 04-22-06 at 08:07 AM. Reason: change "GRods" to "GE's"
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Old 04-22-06, 08:15 AM
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Bill, I am not sure what you are trying to say.

The GEC (grounding electrode conductors) are connected to the Neutral at the main panel or switch. The ECG and its buss bar are bonded to the neutralbar at this same location only. These can be the same buss bar in this switch or panel.

In a sub panel the ground bar and neutral bar must be seperate, and the neutral bar must be mounted on insulators.
 
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Old 04-22-06, 08:34 AM
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Jwhite, basically the debate (in a thread by the same name in this area of this forum) was where the GEC is supposed to land, if the neutral and grounding bars are seperate (as in bonded, but physically two seperate bars) in a disconnecting means in a detached structure, fed with a "no-EGC" feeder, per 250.32(B)(2).
 
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Old 04-22-06, 08:53 AM
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I just read the other thread and re-read 250.32
250.32(B)(2) does not apply.

The ground and neutral bars should be seperate in this panel and the ground rods should be connected to the ground bar.
 
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Old 04-22-06, 09:24 AM
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Right - that installation fell under (B)(1). Any discussion of a (B)(2) installation on that thread would be inconsiderate and confusing to the original poster, which is why Bill found it necessary to start his own thread to discuss (B)(2), about where the GEC is supposed to land in the (B)(2) scenario.

So this discussion is inspired by, but not relevant to, the other thread.
 
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Old 04-22-06, 09:48 AM
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Thanks for clearing that up Rocky Mountain.

If this is a B 2 installation then the ground and neutral bars would be bonded and therefore the same bar. The GEC could be landed in any terminal where it will fit on either bar.
 
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Old 04-22-06, 09:23 PM
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Some AHJs want the EGC tied to the neutral buss in a main panel. Period. Doesn't matter that the neutral buss is bonded to the ground buss, they want the 2 wires physically on the same bar. Some of this has to do with the total number of connections involved getting from the neutral to the EGC, and the pathway involved. Most AHJs who want the EGC on the neural buss bar in a main panel also want a 3 wire feed to a sub panel in a separate structure wired the same way. I have drawings from several AHJs indicating the EGC is to be on the neutral buss bar and not putting it there for these folks gains you a tag to get it changed before the final will be OK'd There's more to this business than reading the code book.

Not everyplace has adopted the 2005 NEC. Not all places require AFCIs, some that do don't want them on smoke detectors. Some places exempt the wall space behind the area an open door covers from the receptacle spacing rules, some don't. Some places want 2 ground rods, some don't care. You get the idea - there is no everytime, everywhere. And where I do some of my work, these rules change from one side of the street to the other.
 
  #9  
Old 04-24-06, 01:07 PM
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It is my fault that 250.32(B)(2) was brought up on that thread and I am sorry that it got so confusing.

I agree that in the original post that 250.32(B)(2) did not apply, but I stand behind my initial accessment that it was neccesary to know if there was an equipment grounding conductor brought with the feeder to properly answer the question about grounding and bonding the panel in the garage.

Chris
 
  #10  
Old 04-25-06, 08:13 PM
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When it comes to bonding neutrals and grounds together or not. Where ever the system starts from I bond the neutral to ground whether it is a meter pan or transformer and so forth. In sub-panels they shouldn't require to be bonded. If you do bond the neutral to the ground, it will create a parallel circuit and one can get hurt. I don't have my code book here with me but if I'm incorrect please let me know. I practice this and have always passed inspections. I'm just trying to help by putting it in layman's terms.
 
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