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Old 04-30-2011, 12:00 PM   #1
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Subpanel and grounding


Hi,
I have a question about grounding a subpanel, and despite searching through old posts, I don't see that my specific question has been addressed. Here's the scenario:

I am building a shop in my basement which will be served by a 60amp subpanel. My main panel is almost full, so I am installing a small second subpanel next to it to feed the shop sub, and to be available for future expansion if needed. I am running 6-3 to the small sub and then another run of 60 feet or so of 6-3 to the shop sub.

In both subs, I have isolated the neutral and ground bars. The ground from the 6-3 is attached to the ground bar in both subs and then to the ground in the main panel. My friend, who is a journeyman electrician, has suggested that we run a second, independent ground (6AWG THHN) from the sub ground bar to the water service entrance (where the main panel ground is connected.)

Is this second ground ok? Any advantages or disadvantages to doing this?

Thanks!

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Old 04-30-2011, 12:59 PM   #2
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Subpanel and grounding


No advantage and not required. The ground you pulled from the main panel is all you need and all that is required. Ground rods for sub panels are only required when the sub panel is located in an unattached structure. Your garage is attached and therefore requires no additional grounding electrodes or plates.

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Old 04-30-2011, 03:42 PM   #3
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Subpanel and grounding


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Originally Posted by seismichippo View Post
In both subs, I have isolated the neutral and ground bars. The ground from the 6-3 is attached to the ground bar in both subs and then to the ground in the main panel. My friend, who is a journeyman electrician, has suggested that we run a second, independent ground (6AWG THHN) from the sub ground bar to the water service entrance (where the main panel ground is connected.)

Is this second ground ok? Any advantages or disadvantages to doing this?

Thanks!
Check http://www.cable.alcan.com/NR/rdonly...gConductor.pdf for information on equipment grounding conductor (EGC) . Look at table 250.122. It calls for a #10 EGC. You need to install an EGC along with your 3 #6 conductors. These are 2 hot wires + neutral. The neutral and EGC are isolated from each other by connecting each to the isolated neutral and grounding bus bar. This conductor is how you get the grounding terminal on your plugs. You need an EGC from the main panel to both of the sub panels. Not 2 seperate conductors but one. No need to run a #6 to water service. Questions?


Last edited by wareagle; 05-01-2011 at 11:42 AM.
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Old 04-30-2011, 07:53 PM   #4
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Subpanel and grounding


You will be just spending money on wire that you don't have too.....
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