Ground requirements for Sub-sub (?) Panel

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Old 12-13-16, 09:51 AM
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Ground requirements for Sub-sub (?) Panel

Hi -I have a sub panel in my home which is fed from a main breaker located outside. I'm looking to add another sub panel right next to the other one. Do I need to run a ground to a rod from this panel as well? Wasn't 100% sure they are both in the same structure. If not, what all is required for grounding?
 
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Old 12-13-16, 10:22 AM
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The "sub-sub" panel is treated the same way as a "sub" panel.

If it is the first panel in a different building it needs a grounding electrode system, otherwise not.

The grounding electrode system starts with a #6 copper wire from the panel ground bus bar out to two fully buried 8' ground rods at least 6' apart.

Next to its "supra" panel (feeding panel) the panel does not need to be connected directly to ground rods, etc.
 
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Old 12-13-16, 10:41 AM
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Thanks for the reply. I'm not sure I was clear in my original posting. Perhaps I am also not clear as to the definition of a "different building".

All panels are located on/in the same building (My house). The main panel is mounted on the outside of my house below the meter.

That then feeds into the first sub-panel in my basement. This panel has grounds going to my water meter and to a single rod outside using solid #6.

I am looking to install a 2nd sub-panel right next to the one above and am wondering what the grounding requirements are. Will this one also require a #6 to a rod?
 
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Old 12-13-16, 10:59 AM
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The main panel is mounted on the outside of my house below the meter.
That is the only panel that should have a ground rod and bonding to the water pipes if metallic.
That then feeds into the first sub-panel in my basement. This panel has grounds going to my water meter and to a single rod outside using solid #6
That ground/bond should have been at the main panel. Does the first sub panel have two hots. one neutral, and one ground, four wires? All panels are in the same structure so only the first panel with a fuse or breaker, your main panel, should have a ground rod and bonding to the plumbing.
 
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Old 12-13-16, 11:04 AM
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Good question. When I get home later I can double check and provide specifics. The good news is that everything up to this point of adding the 2nd sub panel has all been inspected and approved, so I haven't been too concerned with something being done incorrectly if he was OK with it.
 
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Old 12-14-16, 10:13 PM
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Ray - Good thing I double checked. You are correct and I was totally wrong.

The main panel does indeed have a ground going to a single rod and another ground going to the water main. (Another user mentioned that I should have 2 rods.. is this correct? Inspector already passed me with a single rod, so just curious.. wouldn't be hard to add another one if it provides any extra safety)

The only grounding in my first sub panel (other than the ground coming in from the main panel) is the green screw in the grounding bar that I believe is used to ground the panel itself.

So now my question is this... does the 2nd sub panel need a similar green screw? I had to purchase a grounding bar since one did not come with the panel. If I do indeed need that screw to ground the panel, I'm having a difficult time finding one the correct size/length. Perhaps I need to order it special or check an electrical supplier instead of finding one at the big box stores?

Thanks for the help!
 
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Old 12-14-16, 10:36 PM
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The only grounding in my first sub panel (other than the ground coming in from the main panel) is the green screw in the grounding bar that I believe is used to ground the panel itself.
It may be grandfathered but under current code you must have a ground bar and an isolated neutral bar. That means no ground screw in the neutral bar. If the panels are not connected by metal conduit there must be four wires including a ground wire to the ground bar.
So now my question is this... does the 2nd sub panel need a similar green screw?
No subpanel should have a ground screw and all should have four wires, H,H,N,G.
 
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Old 12-14-16, 11:06 PM
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Thanks for the help! I should be good to go then. I do have 4 wires coming in from the circuit that is feeding the panel and they are connected with metal conduit.

Here is a photo if that helps. I started to run a #6 to a grounding rod, but since I don't need that I will just remove it it, plug the hole and I should be ready for inspection.

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Last edited by ray2047; 12-15-16 at 06:47 AM. Reason: Crop and enlarge image.
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Old 12-15-16, 06:50 AM
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I do have 4 wires coming in from the circuit that is feeding the panel
I see three. Does the neutral bar have no ground screw? I can't tell
 
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Old 12-15-16, 12:34 PM
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Here's a better photo of just the 2nd sub panel.

The 2 grounds connected to the ground bar are:
1) Circuit feeding the panel
2) Circuit exiting the panel

There is no ground screw in the neutral bar.Name:  20161215_124639.jpg
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