Subpanel Grounding?

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BigOleBob

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I am toying with the idea of doing a side job, don't tell my BA, and i need to install a sub-panel. I was told in my classes through the union that you should never ground the subpanel if the main panel is grounded. I never really understood why you shouldn't do that. Seems like you should. Could anyone care to explain why you shouldn't?
 
Once you leave the main service, the neutral and ground are separate. So your sub-panel will have to hot legs a neutral and ground. The neutral bar is NOT to be bonded to the panel via the green 10/24 screw. Now for the reason.... If you were to bond the neutral to the box, then you will created a parallel neutral. The grounded conductor, or neutral, is grounded at the service. The ground is separate in the field for safety of a ground fault.
 
and by creating the second (parallel) path for the neutral, the egc becomes essentially another neutral, so that any current that is supposed to be travelling on the neutral is now shared on the egc, energizing any conduits, boxes, ceiling grids, metal studs, or metal parts on the way back to the source. the situation becomes worse if the neutral gets damaged, loose or broken, then all the neutral current is now on the egc, and because all the equipment is still functioning properly no one finds out until someone is killed or injured, perhaps an electrician taking apart a piece of coduit or box who unknowlingly becomes part of the circuit. the egc is designed to carry fault current only in order to trip ocpd's, not to be a grounded conductor.
 
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From the G v B section at Mike's fron page:http://mikeholt.com/freegraphics.php?id=gvb

Also this thread:
why to not bond subpanels
 
Where is this subpanel going? If it's in or on a separate structure the neutral may be permitted to be bonded to the EGC at the panel. Look at 250.32(B)(2).
 
The most important item in a subpanel is to seperate the ground and neutral. The neutral buss must be isolated from the box and ground. Local codes may reuire grounding of the subpanel, however.
 
sreeja said:
The most important item in a subpanel is to seperate the ground and neutral. The neutral buss must be isolated from the box and ground. Local codes may reuire grounding of the subpanel, however.
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There is an exception that permits the neutral to be bonded at a subpanel. Look at post 7.
 
Sub panel Grounding

Sub panel Grounding

BigOleBob said:
I am toying with the idea of doing a side job, don't tell my BA,

I am the inspector in 2 small towns, and the assistant in another.

A few days ago I received a request from a local IBEW to provide copy's of permit applications for all of 2007, from the 3 towns.

I wonder if they were trying to catch a moonlighter?

Oh I agree with the advice you have been by the fine people in this forum.
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Subpanel Grounding

Subpanel Grounding

infinity said:
There is an exception that permits the neutral to be bonded at a subpanel. Look at post 7.
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That will change in NEC 2008
 
romeo said:
I am the inspector in 2 small towns, and the assistant in another.

A few days ago I received a request from a local IBEW to provide copy's of permit applications for all of 2007, from the 3 towns.

I wonder if they were trying to catch a moonlighter?
Click to expand...

This would really make me smile. :D
 
I agree with isolating the neutral at the subpanel, but further looking into this section I find something funny I hope maybe someone could clear me up on. In the 2005 handbook article 250.32A Exception, if you look at exhibit 250.17 and 250.18, doesnt that rule out the grounding electrode required in exhibit 250.18. Hopefully some one will be able to knock some sense into me, thanks!
 
Never mention sidework here.. Honestly almost EVERY electrician I know does it and it takes nothing away from good EC's. So that said.. If you have to ask about floating the neutral on a sub panel maybe you should pull in some help in the form of a more experienced person. Pay them something to show up and plan your job then you can build it.
 
wireman71 said:
Never mention sidework here.. Honestly almost EVERY electrician I know does it and it takes nothing away from good EC's.
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That is not exactly the point of my response but we don't discuss that here.

That is just dead wrong.
 
Sub Panels

Sub Panels

I just did a sub panel in a detached shed and the inspector wanted a main breaker (properly bolted) and a ground rod. I undestood this to mean The grounds and neautral were seperate. I pulled four wires in PVC. Is this just a local jusisdiction thing?
 
Subpanel Grounding?

ashtrak said:
I just did a sub panel in a detached shed and the inspector wanted a main breaker (properly bolted) and a ground rod. I undestood this to mean The grounds and neautral were seperate. I pulled four wires in PVC. Is this just a local jusisdiction thing?
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No, it is a NEC requirement. 250.32
 
romeo said:
No, it is a NEC requirement. 250.32
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wouldnt the exception to 250.32 rule out the requirement of the electrode if it is fed from a multi-wire branch circuit and already includes an equipment grounding conductor? Unless Im missing the boat altogether.
 
aksparky said:
wouldnt the exception to 250.32 rule out the requirement of the electrode if it is fed from a multi-wire branch circuit and already includes an equipment grounding conductor? Unless Im missing the boat altogether.
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Yes, the exception removes the requirement for the grounding electrode, but if you have a sub panel at the shed, the conductors to that panel are a feeder, not a branch circuit, and the exception does not apply.
 
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