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Old 08-03-2012, 01:13 PM   #1
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Adding a branch panel


Hi, I ran out of empty spaces in my square d load center. I was told that our codes demand that the branch panel needs its own main breaker located in the branch panel for that panel. I solution is easy enough, I bought a new square d load center to install next to my current one. I will run the two 'hots' to the new panel along with the neutral. I was told that I must do something special with the grounding bus bar in the new panel. Some sort of replacement bus bar that I need to acquire from square d. Does anyne know what this is and how to install it and why? Thanks, Jim

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Old 08-03-2012, 02:03 PM   #2
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Adding a branch panel


You need to keep the neutrals and ground separate in the subpanel, so you need a ground bar kit.
Do not use the green screw that came with the panel, and the nec does not require a main disconnect in a sub as long as they are in the same structure

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Old 08-03-2012, 02:34 PM   #3
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Adding a branch panel


Where are you? While it's not in the NEC to require a main in a sub panel, your local code may require it.

For $50 or so you can get a 20 space Square D Homeline panel with 100A main breaker and 5 breakers at your big box store, so it's not a big deal either way.

As the above post mentioned, the difference in grounding simply means that you can put the branch circuit grounding conductors with the neutrals like you may see in your main panel. You have to purchase a separate ground bar and put the grounding conductors to that bar. The existing neutral bar in the sub panel has to be separate from the ground, which is why you make sure that the green screen isn't inserted, since that bonds the neutral bar to the panel's metal can.

To connect the two panels together I would use a short piece of #2 aluminum SE cable and a 90A breaker in your main panel. You may have to move 2 branch circuits over to the sub panel in order to make room for the breaker that will be feeding the sub panel.

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Old 08-03-2012, 04:42 PM   #4
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Adding a branch panel


Thanks for your answers. I do have one question that will enable me to clarify how this will work. The main panel has the neutal attached to the ground bus. The ground bus attaches to the panel. The panel is grounded to the water pipes. I attach the branch panel via mettalic conduit. I attach the neutral from the main panel to the neutral on the branch panel. Aren't the ground bus bars already have continuity with the neutral wire? If so why do I need to use a bus bar kit? I already ordered them and will install but I need to know where I am wrong. Thanks, Jim
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Old 08-03-2012, 05:14 PM   #5
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Adding a branch panel


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Originally Posted by jpalatine View Post
Thanks for your answers. I do have one question that will enable me to clarify how this will work. The main panel has the neutal attached to the ground bus. The ground bus attaches to the panel. The panel is grounded to the water pipes. I attach the branch panel via mettalic conduit. I attach the neutral from the main panel to the neutral on the branch panel. Aren't the ground bus bars already have continuity with the neutral wire? If so why do I need to use a bus bar kit? I already ordered them and will install but I need to know where I am wrong. Thanks, Jim
Yes, you have it correct, that's the way to do it.

And yes, neutral will be bonded to ground inside your main disconnect, which in your situation is your main panel. But that is the only place you can bond it, it has to be kept separate everywhere else. If you bond neutral to ground in any other panel (or anywhere else in the house) you may have stray current going thru the grounding conductor which means that current may be flowing thru grounded devices in your house, such as the body of your washing machine (a common thing that I find, people call because they feel a slight shock when leaning against the washing machine and touching the sink).
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Old 08-03-2012, 05:24 PM   #6
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Adding a branch panel


The pe-installed bars are "neutral bus bars". The neutral from, the service wire is bonded with these bars.
You may notice on the main panel there is a green screw or strap that bonds the neutral bars to the cabinet, tub, box, or whatever you wanna cal it. This is ok unless there is a disconnect between meter and main.

For sub panels the neutrals and grounds must be isolated, or separate, from each other.
To do this, you would NOT use the bonding screw or strap in the sub panel.
Now the neutral bars are strictly neutral. This is why you need to install separate grounding bus bars.
They screw right into the back of the panel cabinet bonding them together.

The neutral that runs between panels goes from main neutral bar to sub neutral bar, which is not bonded
To the cabinet. Obviously the ground goes from main ground/neutral bar to the separate grounding bar in sub.

This is all assuming the panels are near each other.
Hope that clears it up a bit.
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Old 08-04-2012, 12:48 PM   #7
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Adding a branch panel


Thank you. Now I understand, if I used the neutral bus bars in the branch panel that are not grounded to the panel, I would get "feedback" from the receptacle(whatever) to the neutral. Ahaa!! Thanks a million. Jim
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Old 08-04-2012, 01:04 PM   #8
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Adding a branch panel


the main thing is keeping neutrals and grouds separate from each other.

ONLY in the main panel (if there is no disconnect between meter and main panel) the Neutrals and Grounds are bonded together.
Anything outside of this they must be kept separate. ie:Sub panels, recepticles, etc.

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