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n175h 10-12-2009 10:47 AM

question on the "stubbie" bonding links
 
I've been looking at the "stubbie" "BONDING" link that is at the top of the forum. In the 4th picture from left on top row and the 4th picture from left on bottom row, what is the difference in the two. The text in the top row picture says it is a violation of NEC 200.2B. In the bottom picture it says that both the grounding bar and the neutral bar can contain grounds.

Am I not seeing something? Both pictures appear to do the same result, but have conflicting remarks.

joed 10-12-2009 11:02 AM

What stubbie links?

Speedy Petey 10-12-2009 11:43 AM

Quote:

Originally Posted by joed (Post 339570)
What stubbie links?

The sticky at the top of this forum. :thumbsup:

300zx 10-12-2009 11:59 AM

Quote:

Originally Posted by n175h (Post 339563)
the bottom picture it says that both the grounding bar and the neutral bar can contain grounds.

Am I not seeing something? Both pictures appear to do the same result, but have conflicting remarks.

That i think is the Main Panel the Grounds and Neutrals are connected on the same bar Neutral Bar .With a subpanel you must run 4 wires 2 -Hot 1 Neutral And One Ground gets conected to the Ground Bar alot of times you have to buy it seperate. If this is not what you are talking about Sorry looked at pics but not sure if looking at the right ones. :thumbsup:

n175h 10-12-2009 08:37 PM

Let me see if I can attach the pictures, so we are looking at the same page. Unless I'm missing something it appears both boxes are service entrances with neutral and grounds bonded, yet the first picture declares an NEC violation.

Nope I couldn't get them to attach, but I hope I've copy/pasted the two appropriate pictures.

The only difference I see is the grounding bar in Pic #2 is strapped to the neutral. The grounding bar in Pic#1 is screwed to the box, and the neutral is screwed to the box. Both have a current path, correct?

http://www.dropshots.com/stubbie4#al...09-04/16:50:28

http://www.dropshots.com/stubbie4#al...09-05/08:50:56

Stubbie 10-13-2009 12:10 AM

I know I'm supposed to be fishing....:)

I suppose I should be the one to explain this since the drawing is mine. NEC 200.2 (B) does not allow neutral current to have a path through the metal of an enclosure and use the main bonding jumper to get to the supply side neutral (service neutral). So 200.2(B) requires a grounded conductor to be terminated specifically to a busbar meant for that purpose. Some service equipment has added grounding bars as accessories to the factory neutral bars as the drawing illustrates. These bars are bonded to the metal and any current path to the supply side neutral must rely on the metal of the panel and the main bonding jumper. If I land a grounded conductor on one of these accessory grounding bars the only path to the service neutral is by use of the panel metal and the main bonding jumper. This would be a violation of 200.2 (B).

Only fault current is allowed to use the metal of the enclosure and main bonding jumper to reach the supply neutral.....and then only briefly till the overcurrent protective device opens.

Now the drawing showing the violation has a bit of a curve thrown in. There is a wire jumper installed between the factory neutral bar and the accessory grounding bar. If the jumper was removed then it is a clear violation of 200.2 (B). Notice the grounded conductor terminating on the accessory ground bar in that drawing.
However the drawing was made to cause some thought to be given to NEC 200.2(B) in that there are two paths from the grounding bar to the factory neutral bar and the service neutral. Those being the panel metal and main bonding jumper and the 'wire jumper'. Therefore neutral current will use both paths to get to the service neutral. 200.2 (B) states that the continuity of a grounded conductor with the supply side service neutral cannot be dependant on the metal of an enclosure. In this case it does not depend on the enclosure metal as the 'only path'. It also has the wire path so is it a violation or not? It's clear that neutral current is using the panel metal and the wire path. It's probaly about 50% on the wire and 50% on the metal of the panel. You have a couple violations in my opinion one 200.2 (b) which clearly doesn't want enclosure metal being used as a current carrier for obvious reasons and you also have a neutral to ground connection load side of the supply neutral which is another violation. I consider this a load side bond with ground by virtue of the fact neutral current is using a wire jumper and enclosure metal as paths to the supply neutral. The NEC only allows panel metal to be used as a effective ground fault path.

Now in the other drawing you have service equipment that has a bonding strap provided by the factory intentionally meant to carry neutral current from the busbar on the left to the supply neutral on the right. The main bonding jumper is installed but the difference is the metal of the panel/enclosure and main bonding jumper are not being used by neutral current to reach the supply neutral or service neutral.

300zx 10-13-2009 06:23 AM

Welcome Back Stubbie
 
Good to see you back :thumbup:

tns1 10-13-2009 09:31 AM

Had to read that one a few times to understand there is a difference - the bonding strap in the Siemens panel does not touch the enclosure.

On a related note, I noticed that on the panels I have seen no effort is made to remove the paint where the ground bond strap and/or accessory ground bar bolts to the enclosure. Instead of having a large conductive area (which seems like a good idea), there is only the small ring area where the bolt threads actually touch bare metal. Should I be scraping the paint off for those mountings?

Stubbie 10-13-2009 09:39 AM

Oh I'm still on break but I do check in once and a while....:) Boy have I got some fishing stories to tell...

As to this thread it was appropriate to respond. It is always difficult for someone else to explain the intent of another persons drawings.

Back to the thread for a second.... if I modify the drawing that is not a violation (as shown below) it then becomes a clear violation of 200.2(B).

The whole point is that bonded metal is not to be carrying neutral current. Most modern residential 'load centers' are not service equipment only. Meaning that the neutral busbar or busbars when used in a load center applied as 'service equipment' are set on insulated standoffs and must have a mechanical means installed to bond the panel metal to the 'effective fault path'. This allows the panel to be used as service equipment (neutral bonded to ground) or as a 4 wire sub-panel when neutral and ground are not to be bonded.
In the drawing as shown grounding conductors can be landed on any of the bus bars but 'grounded conductors' carrying neutral current can only land on the two bus bars joined by the bonding strap. Note that these two busbars are insulated from the panel metal until the main bonding jumper is installed. Since there is not a path back to the source other than the service neutral..... branch circuit grounded conductors and neutrals landed on these two bars will not use the metal of the enclosure for a current path.


http://media6.dropshots.com/photos/4...013/072015.jpg

300zx 10-13-2009 10:00 AM

pics
 
[quote=Stubbie;340083]Oh I'm still on break but I do check in once and a while....:) Boy have I got some fishing stories to tell...[QUOTE]
We want pics not stories :laughing::laughing:

Stubbie 10-13-2009 10:09 AM

Quote:

Originally Posted by tns1 (Post 340081)
Had to read that one a few times to understand there is a difference - the bonding strap in the Siemens panel does not touch the enclosure.

On a related note, I noticed that on the panels I have seen no effort is made to remove the paint where the ground bond strap and/or accessory ground bar bolts to the enclosure. Instead of having a large conductive area (which seems like a good idea), there is only the small ring area where the bolt threads actually touch bare metal. Should I be scraping the paint off for those mountings?

Only if you do not have factory mounting holes that are intended for the installation of a grounding bar. Adding ground bars to panels when factory mounting holes are not provided may or may not be acceptable to an inspector but it is a common practice whether technically acceptable or not. And in my opinion is allowed in accordance with NEC 2008 250.12.

Stubbie 10-13-2009 10:11 AM

[quote=300zx;340093][quote=Stubbie;340083]Oh I'm still on break but I do check in once and a while....:) Boy have I got some fishing stories to tell...
Quote:

We want pics not stories :laughing::laughing:
Oh yes I've got pictures....but I am not done fishing yet.....:wink:

n175h 10-13-2009 04:09 PM

Well explained. Now I understand the differences as well as the intent of the code.

Thank you.


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