Ground rod/wire question

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  #1  
Old 11-22-06, 10:46 AM
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Ground rod/wire question

I need to install a ground rod for my detached garage subpanel. I assume the wire from the rod to the panel must be protected, and I was just curious how to get it into the garage? Do I have to run a second conduit(in addition to the feeder) into the building?
 
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Old 11-22-06, 01:04 PM
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First before I forget you want to locate it outside the drip ring of your garage. Next you need to be darn sure of what is underground before you drive it. It really sucks to hit a utility gas line or other conduit.
The grounding electrode conductor is sized by a chart in the NEC that is referenced to the size of the largest ungrounded conductor of the feeder. But generally just run a #6 copper ground wire, These are usually solid uninsulated bare copper wires. This covers up to 200 amp conductors.
It must be protected where it is subject to physical damage in a listed conduit like emt, pvc, rmc..etc. Most just use pvc. It must follow the contour of framing members then exit the outside wall... then run it in a trench to the ground rod. Secure it to the rod with an approved clamp some call these acorn clamps.. Needing physical protection would be if it is exposed running down the outside of the garage before going into the ground. Generally if it can get in contact with a piece of yard equipment or some other type of damaging contact it needs protection from damage.

The ground rod needs to be 5/8" and eight feet in length. It is best to drive it vertically down until it is 6" or so below grade level. The best method to use is renting a rotary hammer with ground rod driving chuck. Some use T post drivers and sledge hammers. If you use a sledge get a 4 or 5 foot length of 2x4 and drill a 1" hole towards the center at one end. Slide this over the ground rod and have a buddy control the ground rod with the 2x4 as you drive it. Or better yet you control it and have your buddy drive it.....

Where it connects in the sub panel depends on whether you have a 3 wire feeder or 4 wire feeder bringing power to the sub.

Roger
 
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Old 11-22-06, 02:48 PM
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I am working on a similar project and have already driven my grounding rod. As a follow-on question, should the trench to the rod be as deep as the trench for the feeder conduit? That would mean the #6 leaves the conduit at about 18" down and is clamped to the rod at the same depth and then covered in dirt.

Thanks.
 
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Old 11-22-06, 03:36 PM
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> should the trench to the rod be as deep as the trench
> for the feeder conduit?

It can be that deep, but only needs to be under the surface of the soil. Often it's just buried under the landscaping mulch or similar cover. However, the inspector will want to see the rod, GEC and acorn clamp before you bury it so don't fill in the hole too soon.
 
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Old 11-22-06, 03:44 PM
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>>It can be that deep, but only needs to be under the surface of the soil. Often it's just buried under the landscaping mulch or similar cover. However, the inspector will want to see the rod, GEC and acorn clamp before you bury it so don't fill in the hole too soon.<<

My main panel ground is connected just under the surface as you describe, which is why I asked the question. It's nice to know that that isn't a Code issue, and I never worried much from a practicality/sensibility perspective because the main panel rod is in a largely inaccessible location. However, the grounding rod for my subpanel is in an area that is a little more vulnerable, so I am inclined to connect at least a foot or so underground. I might even go to the full 18" (and of course not cover until the inspector approves).

Thanks again.
 
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Old 11-22-06, 06:58 PM
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8' is 8'. If you need, run the cable up thru sch. 80 pvc. if you use a metal conduit, be sure to bond it.
This will protect the cable. Use a direct burial listed connector on the rod.
 
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Old 11-22-06, 11:11 PM
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Deeper is better

Best practice on those ground rods would be to drive them through the bottom of the trench so that they will be deeper driven by the depth of the trench. The performance of the rods will be drastically improved if they are driven below the permanent moisture depth. If there are critical grounding issues in the building such as computers and other expensive electrical utilization equipment then the first twenty five feet of the trench should be thirty to thirty six inches deep and the Grounding Electrode Conductor should be # 2 bare copper connecting the rods which are then driven below the permanent moisture level at least twenty feet apart. I'm in no way suggesting that is required by the US National Electric Code (NEC). What I am saying is that it will greatly improve the grounding of the entire installation.

In any case two rods are required by the NEC unless testing acceptable to the Authority Having Jurisdiction or AHJ; read the local electrical inspection authority; demonstrates that the first rod has a impedance to earth of twenty five ohms or less. Most installers just drive two rods and let it eat but that is certainly not best practice.
 
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Old 11-29-06, 06:25 AM
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Another quickie question on this...

From the sounds the only place the ground wire needs protection is where it comes out of the ground and into the building? In other words the horizontal run of the bare copper underground does not require protection?

Thanks again! Just trying to get things correct before I call the inspector!

Craig
 
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Old 11-29-06, 07:02 AM
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Yes, you only protect it where it exits the ground and is exposed outside generally. Inside if you follow the framing members it does not need protection. Check with your inspector he may allow sch.40 pvc instead of sch.80. for protection on the grounding electrode conductor. Using 80 will not require approval but it generally is not available at the diy stores.

Roger
 
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