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-   -   Sub Panel Ground and Neutral (http://www.diychatroom.com/f18/sub-panel-ground-neutral-91668/)

COLDIRON 01-08-2011 07:58 AM

Sub Panel Ground and Neutral
 
Help me understand. Sub panel install 2hots, 1 neut, 1 grnd. Separated ground and neutral at Sub panel. Why when they both go back to main panel and can be tied into the same neut/grnd bar. My thought is back feed if they were tied together in the Sub panel. Any info would be appreciated.

Jim Port 01-08-2011 09:20 AM

If they were tied together at a subpanel you could have current flowing on exposed metal parts and creating a shock hazard.

awdblazer 01-08-2011 09:50 AM

neutral and ground should be isolated from each other at the main panel not at the sub panel

joed 01-08-2011 09:54 AM

Quote:

Originally Posted by awdblazer (Post 565365)
neutral and ground should be isolated from each other at the main panel not at the sub panel

Wrong advise. The neutral and ground are tied together one point on a residential service, the first main disconnect. Usually that is the main panel, but sometimes there is a disconnect before the main panel. Everywhere else the ground a neutral are isolated.

a7ecorsair 01-08-2011 10:28 AM

I'll add a little more to what JP said.
The neutral, which is correctly called the grounded conductor, is a current carrying conductor and has current flowing in it any time you have a 120 volt circuit active.
The ground, correctly called the grounding conductor, does not normally carry current. The only time this sees current is in a fault condition which is why it is allowed to be bare within the NM cable.
If the neutral and ground were tied together in the sub panel, which wire would carry the 120v neutral current?
Your main panel is different because it is connected directly to the POCO transformer with three large wires. Your house is really a MWBC so the only current on the neutral, it is a true neutral at this point, is the imbalance between the two bus bars.
The neutral and ground bus are tied together and connected to the GEC. One thing this does is reference your system to earth potential. The POCO transformer probably has a ground wire from the secondary center tap to earth ground too so it is reference to earth potential at that point also.

COLDIRON 01-08-2011 11:16 AM

Thank You all for the responses I got it.

oleguy74 01-08-2011 11:49 AM

also if you were to lose the neutral between sub panel and main,your load would be going through your ground.which will be bad.


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