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#94107 - 07/06/05 06:04 PM sub panel without equipment ground?  
royta  Offline
Member
Joined: Sep 2004
Posts: 138
CA
A customer has a sub-panel on an the inside of an exterior wall of a barn type building. I need to remove this panel and install a new panel on the other side of the wall (outside of the building). I guess that doesn't really matter to you.

Here's my situation. There is a meter/main combo on the side of the house which feeds a sub-panel located in the house. The main panel also fed a 240V branch circuit going to a disconnect located at the back of the house. Somebody before me removed the interior of the disconnect and used it as a junction box to feed the same sub-panel I am trying to relocate. Here's the problem, there is no equipment ground between the main and sub-panel. There are only two 120V legs and a Neutral between the two panels. For ground at the sub-panel, there is a grounding electrode. I am trying to squeeze under 2002 NEC 250.32(B)(2) and bond the neutral bar to the sub-panel can. It would be easy to pull an equipment ground between the junction box and the sub-panel, however it won't be so easy to get a ground between the junction box and the main panel (both are on exterior walls of the house). I qualify under parts 1 & 2 of the Article, but part 3 seems to catch me. Where...ground-fault protection of equipment has not been installed on the common ac service. Since this is a residential installation, there is obviously ground-fault protection located somewhere in the house. However, it is not coming from the main panel, only the sub-panel located in the house. Does this still fall under the "common ac service"? Besides this, the junction box (old disconnect), contains splices of the current carrying conductors feeding the barn sub-panel.

What can I legally get away with?


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#94108 - 07/06/05 10:12 PM Re: sub panel without equipment ground?  
winnie  Offline
Member
Joined: Sep 2003
Posts: 649
boston, ma
I am not sure about the exact wording here, which _might_ cause problems if there are GFCIs on branch circuits. However, as far as the _reason_ for part 3 of this article, GFCIs on branch circuits are not relevant.

The issue is ground fault detection on the entire service. A bond between neutral and ground at the subpanel would be a connection between circuit conductors and ground downstream of this ground fault detection. Depending upon how the ground fault detection is implemented, such a bond could desensitize the ground fault detection or could cause false tripping.

I rather doubt that this residence has service ground fault protection [Linked Image]

-Jon


#94109 - 07/06/05 10:15 PM Re: sub panel without equipment ground?  
royta  Offline
Member
Joined: Sep 2004
Posts: 138
CA
Excellent. It looks like I go back tomorrow and finish the job. Thanks.

Roy


edit -- How do I bond the junction box? Do I attach the Neutral to it?

[This message has been edited by royta (edited 07-06-2005).]


#94110 - 07/06/05 11:46 PM Re: sub panel without equipment ground?  
winnie  Offline
Member
Joined: Sep 2003
Posts: 649
boston, ma
It sounds to me like the 'junction box' is on the side of the building with the service. Since 250.32(B)(2) applies to _detached_ structures, it seems to me like you would have to run an equipment ground to the junction box...which on re-reading your original post seems to be the problem.

Remember that the only time you can run a subpanel like a 'service' with bonded ground and neutral is if the subpanel is in a detached structure with no metallic pathways between the two structures.

-Jon



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