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| My service goes from the meter on a pole outside to a main disconnect breaker in my detached garage. From there four wires go underground to the house where there is a main breaker and all the cicuits. In the house the grounds and neutrals are separated and there are 2 ground rods.
From the panel in the house, a 40 amp breaker feeds back to a subpanel in the garage mounted right next to the main disconnect breaker. The subpanel has a ground bar and there are 2 ground rods outside. The main disconnect has a bonding screw and a ground wire going to the ground bar in the subpanel.Is this setup right? It seems that now the neutrals and grounds are connected through the ground wire from the main disconnect to the ground bar in the subpanel. |
Follow-Up Postings:
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| The ground rods should be out at the disconnect, not at a sub-panel in the same building. Sun-panels require isolation of grounds and neutrals and no connection between the two. They do not require ground rods if they are in the same building. |
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- Posted by ronnatalie (My Page) on Wed, Dec 14, 11 at 16:31
| Brick is right. I suspect the main disconnect was moved from the house to the garage at some point, leaving the current hodgepodge. |
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- Posted by bushwacker1 (My Page) on Thu, Dec 15, 11 at 7:19
| So let me get this correct. The ground rods for the garage should be connected to the ground in the disconnect in the garage and the subpanel fed from the house but located in the garage should not be connected to these ground rods?? Sorry this is confusing. |
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| The only place there should be ground rods is at the main where the groundING (AKA 'safety ground') and the groundED (AKA 'neutral' from the POCO) are bonded together in a single building. Sub panels are re2uired to be served by a 4-wire connection (2 hots, 1 neutral, 1 ground) and if they are in the same building do not require ground rods. The rods are at a single place in a building, then main panel that has ground and neutral bonded. |
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- Posted by bushwacker1 (My Page) on Thu, Dec 15, 11 at 12:16
| Ok, the fact that the sub panel in the detached garage is fed from the house doesn't make any difference? Thanks for all your help! |
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- Posted by weedmeister (My Page) on Thu, Dec 15, 11 at 15:47
| What is the distance from the detached garage main breaker panel to the house subpanel? |
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| I did not notice you said detached garage in the first post. If the garage is detached from the house then the first panel in the house is a sub-panel and requires ground rods. Any panel fed from the first house panel requires a 4-wire feed but does not require ground rods. Having additional ground rods on a panel that does not require them is probably not a good idea. The earth is a poor conductor at 120 V. The rods are for lightning and pole transformer leakage (the earth IS a good conductor at 7,200 V, the lowest normal distribution voltage). If another panel is being fed from the main back in the garage it should be a sub to the house wit isolated neutral and ground and be bonded to the ground in the disconnect. I would think very hard about adding an overcurrent device and feeding the box in the garage as a sub directly from the disconnect. The whole 'exiting a separate building and then going back into it to supply power' just makes me uncomfortable. I would be worried that a voltage could exist on the garage sub-panel relative to the disconnect.
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- Posted by bushwacker1 (My Page) on Fri, Dec 16, 11 at 13:31
| "Any panel fed from the first house panel requires a 4-wire feed but does not require ground rods. Its ground is in the 4-wire feed." The panel I'm asking about is in a detached garage. My original question was about this panel. I'll try to reword the ?. If the panel in the garage is on the same ground rods as the main disconnect in the garage isn't that mixing the bond and the ground? And is this permitted? |
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- Posted by ronnatalie (My Page) on Fri, Dec 16, 11 at 17:01
| Each structure is required to have only one ground. You can fix this by bonding all the ground rods together (probably more preferable than ripping out the spurious ones). It's pretty darned unambiguous in the code: Where an ac system is connected to a grounding electrode in or at a building or structure, the same electrode shall be used to ground conductor enclosures and equipment in or on that building or structure. Where separate services, feeders, or branch circuits supply a building and are required to be connected to a grounding electrode(s), the same grounding electrode(s) shall be used. Two or more grounding electrodes that are bonded together shall be considered as a single grounding electrode system in this sense. |
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